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PERILOUS PLASTICS? • CARBON PROPHET • HOT WIRING NERVES
AMERICAN
Scientist January–February 2010
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Robotic Chemistry on Mars
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AMERICAN
Scientist Departments
Volume 98 • Number 1 • January–February 2010
Feature Articles
2 From the Editor
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3 Letters to the Editors 6 Macroscope A short history of hydrogen sulfide Roger P. Smith 10 Computing Science A tisket, a tasket, an Apollonian gasket Dana Mackenzie
48 Neural Interfaces Bioengineers seek to connect the nervous system to implanted devices Warren M. Grill
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16 Engineering Occasional design Henry Petroski 20 Marginalia You’ll never guess who walked in! Pat Shipman 24 Science Observer A magic number?• That sinking feeling • In the news
30 Assessing Risks from Bisphenol A Animal studies suggest that trouble may be afoot with endocrine disruptors Heather Patisaul 58 American Scientist Classics: Carbon Dioxide and the Climate Two commentators revisit a 1956 article by physicist Gilbert N. Plass James Rodger Fleming and Gavin Schmidt
68 Sightings Real-deal connectivity
Scientists’ Bookshelf 70 Book Reviews Evocriticism • Eco-devo • Microbe evo • Microbe scale
From Sigma Xi 90 Distinguished Lectureships, 2010–2011 93 Sigma Xi Today Crosby elected president • Gilmore elected treasurer • Outstanding chapters honored
40 40 Phoenix on Mars The lander has made new discoveries about water on the red planet Walter Goetz
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The Cov er More than a hundred exposures taken by the Phoenix lander’s surface stereo imager camera were combined and projected as if the viewer is looking down from above to create this remarkably clear image of the spacecraft millions of miles away on the surface of Mars (cover). The black circle is where the camera itself is mounted to the craft, an area that is out of the field of view of the camera. In “Phoenix on Mars” (pages 40–47), Walter Goetz describes the scientific studies that the lander has carried out on-site in the Martian polar region, including analyses of soil chemistry and water ice, often using its robotic arm (left). Phoenix has also made detailed observations of Martian weather and the complete water cycle on the red planet. (Images courtesy of NASA/JPL-Caltech/University of Arizona/Texas A&M University.)
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From the Editor
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In with the Old; in with the New
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his issue arrives in your hands a scant two years prior to American Scientist’s centennial year. From 1913 until 1943, the publication was known as Sigma Xi Quarterly, and much of its content was devoted to Society news, along with transcripts of lectures given by its most illustrious members. Since 1943, the publication has been known as American Scientist and has been largely devoted to describing the very best that science and engineering have had to offer. Starting in 1970, American Scientist adopted the current magazine format and increased its frequency to six times per year, changes that allowed it to do more of what it had been doing so well even better than it had before. We plan to celebrate this milestone in a variety of ways, but one of the most important is to take a look back at some of the seminal articles the magazine has published over the years. A number of those are already included under the heading “Classics” at American Scientist Online, and we plan to add many more, but a few merit even more attention and will be republished in this and future issues. “Carbon Dioxide and the Climate,” by Gilbert N. Plass, appeared in the July 1956 issue of American Scientist, and many would say that it, and a similar article by Plass that appeared later that year in Telus, marked the beginning of modern climate science. As the timeline that accompanies the article indicates, the notion of the
so-called greenhouse effect goes back to the early 19th century, but it was Plass’s work that placed carbon dioxide into the context that was then available about how climate was changing and concluded that its role accounted for the data better than competing theories. Plass’s article (see pages 58–67) could speak well for itself 54 years after the fact—indeed, I was taken aback by its prescience when Brian Hayes first pointed it out to me—but we thought it better to let people who know the topic put the work in perspective. We therefore asked James Rodger Fleming, a science historian at Colby College, and Gavin Schmidt, a climate modeller with NASA Goddard Institute for Space Studies, to comment on the place of Plass’s work in both the history and science of climate research. I think you will agree that it was a remarkable achievement, but you’ll also find out that he couldn’t help it if he was lucky.
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long with the old revived, we have something entirely new to offer. Each month during the academic year, Sigma Xi and American Scientist host something we’ve come to call “Pizza Lunch” here at the Sigma Xi Center in Research Triangle Park, North Carolina. We invite scientists and engineers from the area’s major research universities and institutions to give informal talks about their work. The audience is mainly science and technology communicators, so the content is accessible by the general public. Why not, we wondered, offer recordings (with slides, as appropriate) of the talks as podcasts? Indeed, and now— thanks to the efforts of Elsa Youngsteadt, Michael Heisel and Greg Ross—there are three to choose from. Just point your browser to www.americanscientist. org/science/page/pizza-lunch-podcasts and enjoy! Sorry, but we have yet to figure out how to deliver virtual pizza.—David Schoonmaker
American Scientist David Schoonmaker Editor Morgan Ryan Managing Editor Fenella Saunders Senior Editor Catherine Clabby Associate Editor Mia Smith Editorial Associate Barbara J. Aulicino Art Director Tom Dunne Assistant Art Director Brian Hayes Senior Writer Christopher Brodie Contributing Editor Rosalind Reid Consulting Editor Elsa Youngsteadt Contributing Editor
Scientists ’ Books he l f Flora Taylor Editor Anna Lena Phillips Assistant Editor
Amer ican S ci e nt i s t Online Greg Ross Managing Editor www.americanscientist.org
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Jerome F. Baker Publisher Katie Lord Associate Publisher Jennifer Dorff Marketing Manager
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Letters to the Editors In Defense of R. A. Fisher
To the Editors: Together with A. W. F. Edwards, I was the last undergraduate student of R. A. Fisher (in genetics in Cambridge, 1956–57). The comment by Hari Dayal and Alok Kalia, and to a lesser extent, the reply by Andrew Gelman (November–December 2009) does a great injustice to Fisher. It is clear that none of the protagonists have read the paragraph in Statistical Methods for Research Workers in which Fisher introduced, in a delightful way, the P < 0.05 level of probability as the threshold that people, who do not understand tests of significance, religiously adhere to. Commenting on his new table of χ2 and probabilities, the two paragraphs on pages 79 and 80 of the first edition (1925) read: In preparing this table we have borne in mind that in practice we do not want to know the exact value of P for any observed χ2, but, in the first place, whether or not the observed value is open to suspicion. If P is between 0.1 and 0.9 there is certainly no reason to suspect the hypothesis tested. If it is below .02 it is strongly indi-
cated that the hypothesis fails to account for the whole of the facts. We shall not often be astray if we draw a conventional line at .05, and consider that higher values of χ2 indicate a real discrepancy. To compare values of χ2, or of P, by means of a ‘probable error’ is merely to substitute an inexact (normal) distribution for the exact distribution given by the χ2 table. Although relating directly to χ2, these comments are generally applicable. Fisher revolutionized experimental science at Rothamsted Experimental Station. By “tackling small sample problems on their merits,” he introduced the concepts and techniques of degrees of freedom, null hypothesis, relevant subset, analysis of variance, an efficient statistic, sufficiency, likelihood, maximum likelihood, test of significance, information, the current standard table of χ2 (with the consequential layout of the other statistical tables that he worked out by pencil and paper methods) and others. Most have a direct application in almost every field of science, engineering, medicine and manufacturing. Thus the comment “To equate agricultural experiments with decisions regarding
patients defies logic” is misleading and downright wrong. David A. Jones, Emeritus Universities of Hull and Florida Don’t Forget the Scale
To the Editors: William A. Shear’s article “Harvestmen” (November–December 2009) on Opiliones is fascinating. It’s no wonder that these insects enthrall the author. The photographs accompanying the text are most illuminating and beautiful. But why did neither author nor editor provide a scale for them? When searching for them, how can we find them without a clue as to their size? Horst Roth Montreal, QC Dr. Shear responds: In the case of Leiobunum species, the most common North American forms are so frequently seen that they are familiar to many people. Generally, their body lengths are in the range of 5 to 10 millimeters, with legs spanning much larger dimensions. In the cases of more exotic species, the dimensions
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American Scientist (ISSN 0003-0996) is published bimonthly by Sigma Xi, The Scientific Research Society, P.O. Box 13975, Research Triangle Park, NC 27709 (919-549-0097). Newsstand single copy $4.95. Back issues $6.95 per copy for 1st class mailing. U.S. subscriptions: one year $28, two years $50, three years $70. Canadian subscriptions: one year $36; other foreign subscriptions: one year $43. U.S. institutional rate: $70; Canadian $78; other foreign $85. Copyright © 2010 by Sigma Xi, The Scientific Research Society, Inc. All rights reserved. No part of this publication may be reproduced by any mechanical, photographic or electronic process, nor may it be stored in a retrieval system, transmitted or otherwise copied, with the exception of one-time noncommercial, personal use, without written permission of the publisher. Second-class postage paid at Durham, NC, and additional mailing office. Postmaster: Send change of address form 3579 to Sigma Xi, P.O. Box 13975, Research Triangle Park, NC 27709. Canadian publications mail agreement no. 40040263. Return undeliverable Canadian addresses to P. O. Box 503, RPO West Beaver Creek, Richmond Hill, Ontario L4B 4R6.
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range from around 2 millimeters in body length for some of the smaller cyphophthalmids to as much as 30 millimeters for a really big Brazilian Gonyleptid. Leg spans of these large species can be as wide as 25 centimeters. A Little Context, Please
To the Editors: The Feature Article by Keith A. Webster, “Mitochondrial Death Channels” (September–October 2009) beautifully illustrates the strength and weakness of much contemporary biomedical research: The strength is its exquisite description of the molecular, cellular and physiological details of a clinically important phenomenon, myocardial infarction, in the contexts of apoptosis, oxidative stress and ischemia-hypoxia. Its weakness is the absence of broader contexts, a common feature of contemporary biomedical research in papers and seminars. The context here is the role of innate immunity in triggering acute myocardial infarction (AMI). Innate immunity,
Illustr ation Credits Page 8
Macroscope adapted by Tom Dunne
Computing Science Page 12 Barbara Aulicino Engineering Page 17 Tom Dunne Assessing Risks from Bisphenol A Figures 2–4, 6 (right), 7 Barbara Aulicino Phoenix on Mars Figure 7 (left) Tom Dunne Neural Interfaces Figures 2–4, 6 (right), 7 Tom Dunne American Scientist Classics: Carbon Dioxide and the Climate Figure 2 Barbara Aulicino
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which is the initial response of the body to infectious, traumatic and toxic stresses comprises many pathways. One of them, the complement pathway, consists of some 30 serum and membranebound proteins that protect against infections, but also damage tissues such as the heart. This pathway is triggered by ischemia, hypoxia and oxidative stress and also mediates apoptosis and myocardial infarction. Knowledge of the participation of this pathway in infarction is important not only because it helps to explain how the heart is damaged but also suggests treatments such as antagonists of this pathway. Moreover, knowledge of this pathway may help to predict and evaluate the success of various treatments. For instance, drugeluting stents employed to reduce the narrowing of blood vessels in the heart can trigger the complement pathway and thereby induce significant inflammation that impairs vascular healing and leads to renarrowing of the vessels. The absence of broader context in much contemporary biomedical research reflects either the lack of knowledge of that context (for example, innate immunity and the complement pathway), or failure to consider the context germane. In either case, a byproduct is failure to communicate the broader picture to graduate students, postdoctoral fellows and faculty. This failure is then reflected in the inadequate training that many of our graduate students and postdoctoral fellows receive and the eventual narrow teaching that they themselves do. Abram B. Stavitsky Cleveland, OH Dr. Webster responds: I appreciate Dr. Stavitsky’s comments. Unlike innate immunity, however, the role of the mitochondrial death channels in necrotic and apoptotic death during AMI are now quite well understood. The mitochondrial permeability transition pore (mPTP) is a clear therapeutic target and there are a number of candidates of which, in my opinion, cyclosporine A (CsA), volatile anesthetics and Viagra are the most promising. Each of these agents target the mPTP—CsA directly through its binding to cyclophilin D (CypD), volatile anesthetics and Viagra indirectly by activating ischemic preconditioning and inhibiting GSK3-* upstream of CypD. Clinical trials are underway for
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these agents, each of which is already approved for other indications. And successful results have already been reported where volatile anesthetics are used during angioplasty or CABG. Innate immunity is a much more difficult target. We are not sure whether it is injurious or protective. It is not clear to what extent innate immunity is a consequence rather than a cause of AMI. A central role of innate immunity in coronary artery disease has been recognized for many years, and an exaggerated role of inflammation within damaged vessel walls after angioplasty with or without coronary stenting is indeed a serious clinical concern and the focus of intense research. Activation of innate immunity during myocardial infarction and remodeling has also been recognized for many years and is supported both by animal and patient studies that have demonstrated increased levels of circulating inflammatory cells, cytokines, and complement factors in patients with unstable angina, pre- and post AMI, and post-AMI progressing to heart failure. Support for a direct role of innate immunity in AMI also includes the presence of neutrophils, macrophages and elevated levels of inflammatory cytokines within the infarct and peri-infarct regions of the myocardium. In addition, over-expression of inflammatory cytokines in mouse models can reproduce multiple features of post-MI contractile dysfunction, negative remodeling and heart failure. Despite this, clinical trials targeting either complement or inflammatory cytokines have been largely unsuccessful. This may be because the overall role of innate immunity during human AMI is protective. So, whereas I agree with Dr. Stavitsky that graduate students and postdocs should be made aware of the roles of innate immunity in cardiovascular disease—at the University of Miami, they are—I am not sure that I have missed a broader context in my article by focusing on the death channels. How to Write to American Scientist
Brief letters commenting on articles that have appeared in the magazine are welcomed. The editors reserve the right to edit submissions. Please include a phone number or e-mail address if possible. Address: Letters to the Editors, American Scientist, P.O. Box 13975, Research Triangle Park, NC 27709 or _________________
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Macroscope
A Short History of Hydrogen Sulfide Roger P. Smith
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arly last year, reports began to emerge in the Southeastern United States of a strange illness. Homeowners reported nosebleeds, sinus irritation and respiratory problems that appeared to be associated with corrosion of copper pipes and air conditioner coils in their houses. The culprit seems to be drywall imported from China and possibly contaminated with strontium sulfide, an unstable salt that releases hydrogen sulfide on exposure to moisture. It was used widely in the housing boom of 2004–2007, and in the rebuilding efforts after Hurricane Katrina in 2005, when domestic suppliers could not keep up with the demand. The Consumer Products Safety Commission is now investigating whether sulfide gases given off by the drywall, including hydrogen sulfide, are to blame. The Florida Department of Health maintains a Web site with information for consumers. Lawsuits abound, and many who are able to do so have moved out of their homes. Several estimates place the number of affected houses at 100,000. To those experiencing or investigating this phenomenon early on, it seemed bizarre. But in fact, this is just the latest chapter in the history of a chemical whose effects were first noted in the 16th century. And there is still more to learn about its role in the human body. Recent research offers insights into its biochemical actions as well as some intriguing suggestions for medical uses. Roger P. Smith is the Irene Heinz Given Professor of Pharmacology and Toxicology, Emeritus, at Dartmouth Medical School and former chair of the department. He served on the Associate Consulting Staff of Mary Hitchcock Memorial Hospital now in Lebanon, New Hampshire, and as a consultant to the V.A. Medical Center in White River Junction, Vermont. He received his Ph.D. from Purdue University. Address: Department of Pharmacology and Toxicology, Dartmouth Medical School, Hanover, NH 03755. Email: _______________
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From the sewers of Paris to physiological messenger Occupational Exposures
In 1713, a remarkable Italian physician named Bernardino Ramazzini published De Morbis Artificum, or Diseases of Workers. In Chapter 14, titled “Diseases of Cleaners of Privies and Cesspits,” he describes a painful inflammation of the eyes which was common among such workers. The inflammation often led to secondary bacterial invasion, and sometimes to total blindness. Displaying amazing insight, Ramazzini hypothesized that when the cleaners disturbed the excrement in the course of their work, an unknown volatile acid was produced, which was irritating to the eyes. It was also at least partially responsible for the odor of excrement, and it is now known to be generated wherever organic matter undergoes putrefaction. Ramazzini further postulated that that same acid was causing copper and silver coins which the workers had in their pockets to turn black on their surfaces—an eerie resonance with the phenomena recently observed by U.S. homeowners. Around 1777, a series of accidents—some of them fatal—began to occur in Paris due to a gas emanating from its sewer system. The commission appointed to study the cases made its findings public in 1785. The report described two distinct types of poisonings: a mild form involving inflammation of the eyes and mucous membranes as already described by Ramazzini, and a severe form that was characterized by a fulminating (rap-
idly developing) asphyxia. It is little wonder that the French Romantic writer Victor Hugo (1802–1885) referred to the Parisian sewers as “the intestine of the Leviathan.” Many years were to pass, however, before chemical analyses would establish the presence of hydrogen sulfide in the sewers and implicate it as the cause of the accidents. The history of exposures has focused 20 carats of genuine on sewers and the workplace, but the mined emeralds. corrosive effects of hydrogen sulfide are Enlarged to show details common knowledge in Rotorua, New Zealand, which was built over centuries in a geothermally active area. The constant exposure to low, environmental levels of hydrogen sulfide produces such damage even as residents enjoy spas, indoor heating and cooking with the hot gases. Today, the American Conference of Industrial Hygienists has set the socalled threshold limit value for its presence in the workplace at 10 parts per million (ppm) of hydrogen sulfide in air for eight hours a day, five days a week over a working lifetime. The U.S. National Institute for Occupational Safety and Health estimated in 1977—some 200 years after the Paris accidents—that 125,000 workers in at least 77 occupations, including drilling for petroleum, tanneries and the paper industry, may be at risk of exposure to hydrogen sulfide. Chemical Discovery
Around 1750, a humble young Swede beginning his career as an apothecary was fortunate to have a series of very understanding mentors who allowed him considerable free time for reading and experimentation. His name was Carl Wilhelm Scheele, and he turned out to be a gifted chemist. Like many chemists before and after him, Scheele seems to have given little thought to the biological effects of the materials with which he worked. One day while distilling potassium ferrocyanide with sulfuric acid, he noted a “strong, pe-
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culiar and not unpleasant odor.” He brought himself to taste this gas and described it as “slightly on sweet [sic] and somewhat heating on the mouth.” Today we describe the odor as that of bitter almonds and call the gas hydrogen cyanide. Scheele may have been fortunate to have escaped with his life. Perhaps a guardian angel was with him again on the day that he treated ferrous sulfide (pyrite, or fool’s gold) with a mineral acid. He called the rank odor that resulted Schwefelluft (sulfur air) and referred to it as stinkende (stinking or fetid). Today we refer to the odor as that of rotten eggs. His patron, the Swedish chemist and mineralogist Torbern Olof Bergman, also demonstrated its presence in some mineral springs. The publication date for these original observations was 1777—around the time of the Paris accidents. The fact that the same man discovered both hydrogen sulfide and hydrogen cyanide was the start of a long series of coincidences and discoveries about the two chemicals that would uncover their similarities. Biological Effects
Investigations on the biological effects of hydrogen sulfide began around the turn of the 20th century. François Chaussier, François Magendie, Claude Bernard and Felix Hoppe-Seyler were among the well-known scientists of the day who labored in that vineyard. In experiments with dogs, marked differences in the effects of hydrogen sulfide were noted with only small changes in its concentration in the air they were breathing. Fifty ppm, which was considered a minimally lethal concentration at the time, resulted in a slight progressive depression in the rate and depth of respirations. After many hours of exposure, the dogs died from a type of pulmonary edema, acute respiratory distress syndrome (ARDS). When that concentration was doubled to 100 ppm, death resulted in 15 to 20 minutes. In these cases the respiration was stimulated almost immediately, this progressed to a pronounced hyperpnea (deep breathing), and death in apnea followed. At 300 ppm, respiratory arrest occurred after a few violent gasps. The same effects on respiration, with the exception of ARDS, were known to occur with injected or inhaled hydrogen cyanide. Mice may be more resistant to the effects of hydrogen sulfide. In a 1964 experiment, www.americanscientist.org
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Copper air-conditioner coils in some Florida homes have corroded so much that they have required replacing multiple times (top). It is likely that the corrosion is the result of abnormally high levels of hydrogen sulfide in the air. The suspected source of the chemical is several brands of drywall imported from China. Drywall from China was also used in rebuilding efforts in Louisiana and Mississippi after Hurricane Katrina, when domestic supplies of drywall ran short. Coils from an air conditioner not exposed to hydrogen sulfide are shown for comparison (bottom). (Photographs courtesy of the Florida Department of Health.) 2010 January–February
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external carotid artery
carotid body
internal carotid artery
nodose ganglion
superior cervical ganglion common carotid artery
The carotid body (purple mass) regulates respiration by sensing changes in the oxygen content of the blood as it flows through the carotid artery (red) to the brain. The carotid body contains chemoreceptors that bind hydrogen cyanide and hydrogen sulfide; when they do so, respiration is first stimulated and then depressed. In severe cases, breathing either of these gases can cause death. In experiments with dogs that were exposed to hydrogen sulfide in concentrations of 100 parts per million, the dogs died in 15 to 20 minutes. The carotid sinus and associated nerves of the cat are shown here; experiments with cats led to the discovery that severing the sinus nerve (yellow), and thus denervating the carotid sinus, eliminated the effects of both chemicals on respiration.
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A Persistent False Trail
carotid sinus
they survived for 10 minutes in an atmosphere of 1,872 ppm and for 20 minutes at 985 ppm. A more complete explanation of the respiratory stimulant effects of hydrogen cyanide and hydrogen sulfide had to await the discovery of the chemoreceptor function of the carotid body (shown above), and the reflex effects that follow the activation of those receptors. The respiratory stimulant effects of cyanide and sulfide could
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lation. When innervation of the sinus was intact, the hyperpnea was accompanied by a fleeting rise in systemic blood pressure, and sometimes by a slowed heart rate (bradycardia). The cardiovascular effects varied with the injection site and the species and are still not adequately explained.
glossopharyngeal nerve
sinus nerve
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be completely abolished by severing the sinus nerve and thus denervating the carotid sinus. In that case, larger doses of either chemical resulted only in respiratory depression, which was presumably mediated via the brainstem. Similarly, injections of sulfide or cyanide into the internal carotid or vertebral arteries also failed to stimulate respiration, since in those cases the chemicals reached the carotid sinus only after dilution in the general circu-
The great German biochemist HoppeSeyler became famous for his discovery of the abnormal form of hemoglobin known as methemoglobin, in which some or all of the heme irons have been oxidized to the ferric form. This reaction is readily mediated both in vivo and in vitro by sodium nitrite. Methemoglobin cannot reversibly combine with oxygen, and the disruption of the oxygen-transport function of the blood can result in hypoxia and death. In 1863, Hoppe-Seyler passed a stream of pure hydrogen sulfide through a sample of human blood and claimed to have observed a greenish pigment that was associated with shifts in the visible absorption spectrum of hemoglobin. Although he was aware that he had probably produced a mixture containing unstable and denatured products, which resulted in turbidity and precipitation and made the absorption spectra suspect, he still thought that the mixture contained a new form of hemoglobin. He called it sulfhemoglobin and thereby launched one of the most confused areas in hematology. It led to the hypothesis some still subscribe to—namely, that hydrogen sulfide is a blood poison like sodium nitrite and carbon monoxide. No matter that animal experiments clearly demonstrated that it was a respiratory toxin, or that no such pigment has ever been identified in the blood of animals or humans fatally poisoned with hydrogen sulfide. Sulfhemoglobin generated by hydrogen sulfide appears to be a strictly in vitro phenomenon, and it has yet to be prepared in pure form. Sulfmethemoglobin
No less a scientist than Linus Pauling and his associates described the magnetic properties of another blood pigment, which they called sulfmethemoglobin. This pigment is easily prepared in pure form by mixing hydrogen sulfide with methemoglobin, and it is chemically analogous to cyanmethemoglobin, in which the cyanide ion is bound to ferric irons of heme. The
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hydrosulfide anion (HS–) also binds to ferric heme, albeit not quite so tenaciously as cyanide. Indeed, this reaction has been exploited medically as an antidote to cyanide poisoning. One can deliberately inject sodium nitrite intravenously to generate a tolerable level of methemoglobin. The methemoglobin will temporarily bind free cyanide as the inactive complex cyanmethemoglobin. Over time the cyanide is slowly released, at a rate at which the body’s natural detoxification mechanisms can deal with it. At least three laboratories have demonstrated that the same principles can be applied to hydrogen sulfide poisoning and that induced methemoglobinemia can indeed be lifesaving. At least a half dozen successful human resuscitations have been reported in the literature. The odds against its successful application, however, are high. Few poisons are more rapidly acting than inhaled hydrogen sulfide, and inhalation is invariably the route of exposure. Sulfide poisoning tends to occur in remote locations, and there is seldom a medically qualified individual on the scene who is prepared with a parenteral form of nitrite and trained to make intravenous injections. Most successful resuscitations from cyanide poisoning have occurred in individuals who ingested soluble salts of cyanide, where absorption is delayed. Chemical Similarities Between Cyanide and Sulfide
In addition to the similarities in their physiological effects, cyanide and sulfide have chemical similarities. The undissociated forms of both hydrogen cyanide and hydrogen sulfide are flammable, volatile gases. Hydrogen sulfide (whose vapor density, or d, is 1.19) is heavier than air (d = 1.0) whereas hydrogen cyanide (d = 0.941) is lighter. Both are weak acids with acid dissociation constants (pKa) that are of some physiological significance: hydrogen cyanide 9.2–9.3 and hydrogen sulfide 7.04. Both form salts with sodium and potassium as well as with some alkaline earths. Both anions bind to methemoglobin as noted above, and each of those complexes has its distinct visible absorption spectrum. And both are inhibitors of cytochrome c oxidase, the terminal enzyme in the electron transport chain that reacts with molecular oxygen in aerobic organisms. Blockage of that key enzyme is bewww.americanscientist.org
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lieved to be the mechanism of action in the rapidly lethal form of cyanide and sulfide poisonings.
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New Biological Roles
moreceptors in the body. And for all the false leads, in the end it may yet turn out to have some useful applications in medicine—even if only a new Viagra.
Inhibition of cytochrome c oxidase results in a decrease in oxidative phosphorylation (the metabolic pathway that produces ATP). This in turn lowers the metabolic rate and body temperature in mice. These phenomena accompany states of suspended animation. When mice were exposed to hydrogen sulfide at concentrations of 80 ppm, dramatic effects were observed in the first 5 minutes. By 6 hours, their metabolic rate had dropped by 90 percent and body temperature to 2 degrees Celsius above ambient temperature. When the mice were then returned to room air, the metabolic rate and temperature returned to normal with no detectable behavioral or functional deficits. As already noted, lethal levels for hydrogen sulfide in mice are much higher than for dogs, but this state in mice must also occur over a fairly narrow range of concentrations. Finally, and most astonishingly of all, experimental evidence contributed in 2008 indicates that like carbon monoxide and nitric oxide, hydrogen sulfide is an important signaling molecule in biology, and it may find a role in medicine. It is physiologically generated in mice by cystathionine γ-lyase, and genetic deletion of that enzyme markedly reduces hydrogen sulfide levels in the serum, heart, aorta and other tissues. Mutant mice lacking the enzyme have marked hypertension and diminished endothelium-dependent vasorelaxation, consistent with an important vasodilator role for hydrogen sulfide. The enzyme is physiologically activated by the calcium-binding protein calmodulin, which is a mechanism for hydrogen sulfide formation in response to vascular activation. Thus, hydrogen sulfide appears to be a physiologic vasodilator and regulator of blood pressure. Its relative contribution vis-à-vis the similar nitric oxide is not yet clear. What a strange and wondrous journey this odiferous and violently toxic chemical, associated with the excrement of humanity, has led us on for five centuries. It’s a history that could fill a book, one that covers a vast range of territory, from the search to determine the cause of workplace injuries to fascinating discoveries about how hydrogen sulfide interacts with che-
Blackstone, E., M. Morrison and M. B. Roth. 2005. H2S induces a suspended animation—like state in mice. Science 308:518. CPSC/EPA/HUD/CDC/ATSDR Press Statement on Initial Chinese Drywall Studies. October 2009. http://www.cpsc.gov/info/ drywall/oct2009statement.pdf. __________________ Accessed November 17, 2009. Coryell, C. D., F. Stitt and L. Pauling. 1937. The magnetic properties and structure of ferrihemoglobin (methemoglobin) and some of its compounds. Journal of the American Chemical Society 59:633–642. d’Emmanuele di Villa Bianca, R., et al. 2009. Hydrogen sulfide as a mediator of human corpus cavernosum smooth-muscle relaxation. Proceedings of the National Academy of Sciences of the USA 106(11):4513–4518 . Hugo, V. 1938. Les Miserables. Translated by L. Wraxall, illustrations by L. Ward. New York: The Heritage Press. Mellor, J. W. 1930. A Comprehensive Treatise on Inorganic and Theoretical Chemistry. Vol. X. Hydrogen Sulfide. London: Longmans, Green and Co. Mitchell, C. W., and S. J. Davenport. 1924. Hydrogen sulphide literature. Public Health Reports 39:1–13. Partington, J. R. 1962. A History of Chemistry, Vol. 3, Chapter VI. Chemistry in Scandinavia. II. Scheele. London: Macmillan and Co., Ltd. Ramazzini, B. 1940. Diseases of Workers. The Latin text of 1713, revised, with translations and notes by W. C. Wright. Chicago: University of Chicago Press. Smith, L., H. Kruszyna and R. P. Smith. 1977. The effect of methemoglobin on the inhibition of cytochrome c oxidase by cyanide, sulfide or azide. Biochemical Pharmacology 26:2247–2250. Smith, R. P., and R. E. Gosselin. 1964. The influence of methemoglobinemia on the lethality of some toxic anions. II. Sulfide. Toxicology and Applied Pharmacology 6:584–592. Smith, R. P. 1979. 4. Effects on Animals. In Hydrogen Sulfide, A Report by the Subcommittee on Hydrogen Sulfide (chaired by R. P. Smith) of the Committee on Medical and Biologic Effects of Environmental Pollutants, Assembly of Life Sciences, National Research Council, National Academy of Sciences, Washington, D. C., 1977. Reprinted by University Park Press, Baltimore, 1979. Smith, R. P. 1996. Toxic responses of the blood. In Casarett and Doull’s Toxicology: The Basic Science of Poisons, 5th edition, edited by C. D. Klaassen. New York: Macmillan. pp. 335–354. Wayne, Leslie. 2009. Chinese Drywall Found to Differ Chemically. The New York Times, October 29, 2009. Yang, G., et al. 2008. H2S as a physiologic vasorelaxant: Hypertension in mice with deletion of cystathionine γ-lyase. Science 322:587–590.
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A Tisket, a Tasket, an Apollonian Gasket Dana Mackenzie
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n the spring of 2007 I had the good fortune to spend a semester at the Mathematical Sciences Research Institute in Berkeley, an institution of higher learning that takes “higher” to a whole new extreme. Perched precariously on a ridge far above the University of California at Berkeley campus, the building offers postcard-perfect vistas of the San Francisco Bay, 1,200 feet below. That’s on the west side. Rather sensibly, the institute assigned me an office on the east side, with a view of nothing much but my computer screen. Otherwise I might not have gotten any work done. However, there was one flaw in the plan: Someone installed a screen-saver program on the computer. Of course, it had to be mathematical. The program drew an endless assortment of fractals of varying shapes and ingenuity. Every couple minutes the screen would go blank and refresh itself with a completely different fractal. I have to confess that I spent a few idle minutes watching the fractals instead of writing. One day, a new design popped up on the screen (see the first figure). It was different from all the other fractals. It was made up of simple shapes—circles, in fact—and unlike all the other screen-savers, it had numbers! My attention was immediately drawn to the sequence of numbers running along the bottom edge: 1, 4, 9, 16 … They were the perfect squares! The
Dana Mackenzie received his doctorate in mathematics from Princeton University in 1983 and taught at Duke University and Kenyon College. Since 1996 he has been a freelance writer specializing in math and science, and he has frequently edited articles on mathematical topics for American Scientist. His published books include The Big Splat, or How Our Moon Came to Be (Wiley, 2003), and volumes 6 and 7 of What’s Happening in the Mathematical Sciences (American Mathematical Society, 2007 and 2009). Email: ____ scribe@ danamackenzie.com 10
Fractals made of circles do funny things to mathematicians sequence was 1-squared, 2-squared, 3-squared, and so on. Before I became a full-time writer, I used to be a mathematician. Seeing those numbers awakened the math geek in me. What did they mean? And what did they have to do with the fractal on the screen? Quickly, before the screensaver image vanished into the ether, I sketched it on my notepad, making a resolution to find out someday. As it turned out, the picture on the screen was a special case of a more general construction. Start with three circles of any size, with each one touching the other two. Draw a new circle that fits snugly into the space between them, and another around the outside enclosing all the circles. Now you have four roughly triangular spaces between the circles. In each of those spaces, draw a new circle that just touches each side. This creates 12 triangular pores; insert a new circle into each one of them, just touching each side. Keep on going forever, or at least until the circles become too small to see. The resulting foam-like structure is called an Apollonian gasket (see the second figure). Something about the Apollonian gasket makes ordinary, sensible mathematicians get a little bit giddy. It inspired a Nobel laureate to write a poem and publish it in the journal Nature. An 18th-century Japanese samurai painted a similar picture on a tablet and hung it in front of a Buddhist temple. Researchers at AT&T Labs printed
it onto T-shirts. And in a book about fractals with the lovely title Indra’s Pearls, mathematician David Wright compared the gasket to Dr. Seuss’s The Cat in the Hat: The cat takes off his hat to reveal Little Cat A, who then removes his hat and releases Little Cat B, who then uncovers Little Cat C, and so on. Now imagine there are not one but three cats inside each cat’s hat. That gives a good impression of the explosive proliferation of these tiny ideal triangles. Getting the Bends
Even the first step of drawing an Apollonian gasket is far from straightforward. Given three circles, how do you draw a fourth circle that is exactly tangent to all three? Apparently the first mathematician to seriously consider this question was Apollonius of Perga, a Greek geometer who lived in the third century b.c. He has been somewhat overshadowed by his predecessor Euclid, in part because most of his books have been lost. However, Apollonius’s surviving book Conic Sections was the first to systematically study ellipses, hyperbolas and parabolas—curves that have remained central to mathematics ever since. One of Apollonius’s lost manuscripts was called Tangencies. According to later commentators, Apollonius apparently solved the problem of drawing circles that are simultaneously tangent to three lines, or two lines and a circle, or two circles and a line, or three circles. The hardest case of all was the case where the three circles are tangent. No one knows, of course, what Apollonius’ solution was, or whether it was correct. After many of the writings of the ancient Greeks became available again to European scholars of the Renaissance, the unsolved “problem of
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Apollonius” became a great challenge. In 1643, in a letter to Princess Elizabeth of Bohemia, the French philosopher and mathematician René Descartes correctly stated (but incorrectly proved) a beautiful formula concerning the radii of four mutually touching circles. If the radii are r, s, t and u, then Descartes’s formula looks like this:
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a2 +b2+c2+d2 =(a+b+c+d)2/2. As the third figure shows, Descartes’s formula greatly simplifies the task of finding the size of the fourth circle, assuming the sizes of the first three are known. It is much less obvious that the very same equation can be used to compute the location of the fourth circle as well, and thus completely solve the drawing problem. This fact was discovered in the late
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All of these reciprocals look a little bit extravagant, so the formula is usually simplified by writing it in terms of the curvatures or the bends of the circles. The curvature is simply defined as the reciprocal of the radius. Thus, if the curvatures are denoted by a, b, c and d, then Descartes’s formula reads as follows:
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Numbers in an Apollonian gasket correspond to the curvatures or “bends” of the circles, with larger bends corresponding to smaller circles. The entire gasket is determined by the first four mutually tangent circles; in this case, two circles with bend 1 and two “circles” with bend 0 (and therefore infinite radius). The circles with a bend of zero look, of course, like straight lines. (Image courtesy of Alex Kontorovich.)
1990s by Allan Wilks and Colin Mallows of AT&T Labs, and Wilks used it to write a very efficient computer program for plotting Apollonian gaskets. One such plot went on his office door and eventually got made into the aforementioned T-shirt. Descartes himself could not have discovered this procedure, because it involves treating the coordinates of
the circle centers as complex numbers. Imaginary and complex numbers were not widely accepted by mathematicians until a century and a half after Descartes died. In spite of its relative simplicity, Descartes’s formula has never become widely known, even among mathematicians. Thus, it has been rediscovered over and over through the years. In Ja-
An Apollonian gasket is built up through successive “generations.” For instance, in generation 1 (top left), each of the red circles is inscribed in one of the four triangular pores formed by the black circles. The final gasket shown here, whimsically named “bugeye” by Katherine Sanden, an undergraduate student of Peter Sarnak at Princeton University, has circles with bends –1 (for the largest circle that encloses the rest), 2, 2 and 3. The list of bends that appears in a given gasket (here, 2, 3, 6, 11, etc.) form a number sequence whose properties Sarnak would like to explain—but, he says, “the necessary mathematics has not been invented yet.” (Image courtesy of Katherine Sanden.) www.americanscientist.org
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pan, during the Edo period, a delightful tradition arose of posting beautiful mathematics problems on tablets that were hung in Buddhist or Shinto temples, perhaps as an offering to the gods. One of these “Japanese temple problems,” or sangaku, is to find the radius of a circle that just touches two circles and a line, which are themselves mutually tangent. This is a restricted version of the Apollonian problem, where one circle has infinite radius (or zero bend). The anonymous author – – – shows that, in this case, √a + √b = √c , a sort of demented version of the Pythagorean theorem. This formula, by the way, explains the pattern I saw in
the screensaver. If the first two circles have bends 1 and 1, then the circle between them will have bend 4, because – – – √1 +√1 =√4 . The next circle will have – – – bend 9, because √1 +√4 =√9 . Needless to say, the pattern continues forever. (This also explains what the numbers in the first figure mean. Each circle is labeled with its own bend.) Apollonian circles experienced perhaps their most glorious rediscovery in 1936, when the Nobel laureate (in chemistry, not mathematics) Frederick Soddy became mesmerized by their charm. He published in Nature a poetic version of Descartes’ theorem, which he called “The Kiss Precise”:
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Four circles to the kissing come The smaller are the benter. The bend is just the inverse of The distance from the center. Though their intrigue left Euclid dumb, There’s now no need for rule of thumb. Since zero bend’s a dead straight line, And concave bends have minus sign, The sum of the squares of all four bends Is half the square of their sum. Soddy went on to state a version for three-dimensional spheres (which he was also not the first to discover) in the final stanza of his poem. Ever since Soddy’s prosodic effort, it has become something of a tradition to publish any extension of his theorem in poetic form as well. The following year, Thorold Gosset published an ndimensional version, also in Nature. In 2002, when Wilks, Mallows and Jeff Lagarias published a long article in the American Mathematical Monthly, they ended it with a continuation of Soddy’s poem entitled “The Complex Kiss Precise”: Yet more is true: if all four discs Are sited in the complex plane, Then centers over radii Obey the self-same rule again. (The authors note that the poem is to be pronounced in the Queen’s English.) A Little Bit of Gasketry
In 1643 René Descartes gave a simple formula relating the radii of any four mutually tangent circles. More than 350 years later, Allan Wilks and Colin Mallows noticed that the same formula relates the coordinates of the centers of the circles (expressed as complex numbers). Here Descartes’s formula is used to find the radius and center of the fourth circle in the “bugeye” packing. 12
To this point I have only written about the very beginning of the gasketmaking process—how to inscribe one circle among three given circles. However, the most interesting phenomena show up when you look at the gasket as a whole. The first thing to notice is the foamlike structure that remains after you cut out all of the discs in the gasket. Clearly the disks themselves take up an area that approaches 100 percent of the area within the outer disk, and so the area of the foam (known as the “residual set”) must be zero. On the other hand, the foam also has infinite length. Thus, in fact, it was one of the first known examples of a fractal—a curve of dimension between 1 and 2. Even today its dimension (denoted δ ) is not known exactly; the best-proven estimate is 1.30568.
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The concept of fractional dimension was popularized by Benoît Mandelbrot in his enormously influential book The Fractal Geometry of Nature. Although the meaning of dimension 1.30568 is somewhat opaque, this number is related to other properties of the foam that have direct physical meaning. For instance, if you pick any cutoff radius r, how many bubbles in the foam have radius larger than r? The answer, denoted N(r), is roughly proportional to rδ. Or if you pick the n largest bubbles, what is the remaining pore space between those bubbles? The answer is roughly proportional to n1–2/δ. Physicists are very familiar with this sort of rule, which is called a power law. As I read the literature on Apollonian packings, an interesting cultural difference emerged between physicists and mathematicians. In the physics literature, a fractional dimension δ is de facto equivalent to a power law rδ. However, mathematicians look at things through a sharper lens, and they realize that there can be additional, slowly increasing or slowly decreasing terms. For instance, N (r) could be proportional to rδlog(r) or rδ/log(r). For physicists, who study foams empirically (or semiempirically, via computer simulation), the logarithm terms are absolutely undetectable. The discrepancy they introduce will always be swamped by the noise in any simulation. But for mathematicians, who deal in logical rigor, the logarithm terms are where most of the action is. In 2008, mathematicians Alex Kontorovich and Hee Oh of Brown University showed that there are in fact no logarithm terms in N (r). The number of circles of radius greater than r obeys a strict power law, N(r)∼Crδ, where C is a constant that depends on the first three circles of the packing. For the “bugeye” packing illustrated in the second figure, C is about 0.201. (The tilde (∼) means that this is not an equation but an estimate that becomes more and more accurate as the radius r decreases to 0.) For mathematicians, this was a major advance. For physicists, the likely reaction would be, “Didn’t we know that already?” Random Packing
For many physical problems, the classical definition of the Apollonian gasket is too restrictive, and a random model may be more appropriate. A bubble may start growing in a randomly chosen location and expand until it hits www.americanscientist.org
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Physicists study random Apollonian packings as a model for foams or powders. In these simulations, new bubbles or grains nucleate in a random place and grow, either with rotation or without, until they encounter another bubble or grain. Different geometries for the bubbles or grains, and different growth rules, lead to different values for the dimension of the residual set—a way of measuring the efficiency of the packing. (Image courtesy of Stefan Hutzler and Gary Delaney.)
an existing bubble, and then stop. Or a tree in a forest may grow until its canopy touches another tree, and then stop. In this case, the new circles do not touch three circles at a time, but only one. Computer simulations show that these “random Apollonian packings” still behave like a fractal, but with a different dimension. The empirically observed dimension is 1.56. (This means the residual set is larger, and the packing is less efficient, than in a deterministic Apollonian gasket.) More recently, Stefan Hutzler of Trinity College Dublin, along with Gary Delaney and Tomaso Aste of the University of Canberra, studied the effect of bubbles with different shapes in a random Apollonian packing. They found, for example, that squares become much more efficient packers than circles if they are allowed to rotate as they grow, but surprisingly, triangles become only slightly more efficient. As far as I know, all of these results are begging for a theoretical explanation. For mathematicians, however, the classical, deterministic Apollonian gasket still offers more than enough challenging problems. Perhaps the most astounding fact about the Apollonian gasket is that if the first four circles have integer bends, then every other circle in the packing does too. If you are given the first three circles of an Apollonian gasket, the bend of the fourth is found (as explained above) by solving a quadratic equation. However, every subsequent bend can be found by solving a linear equation:
first generation. The other has bend d' = 38, as predicted by the formula, 2+38=2(2+3+15). More importantly, even if we did not know d', we would still be guaranteed that it was an integer, because a, b, c and d are. Hidden behind this “baby Descartes equation” is an important fact about Apollonian gaskets: They have a very high degree of symmetry. Circles a, b and c actually form a sort of curved mirror that reflects circle d to circle d' and vice versa. Thus the whole gasket is like a kaleidoscopic image of the first four circles, reflected again and again through an infinite collection of curved mirrors. Kontorovich and Oh exploited this symmetry in an extraordinary and amusing way to prove their estimate of the function N(r). Remember that N(r) simply counts how many circles in the gasket have radius larger than r. Kontorovich and Oh modified the function N(r) by introducing an extra variable of position—roughly equivalent to put-
d+d'=2(a+b+c) For instance, in the “bugeye” gasket, the three circles with bends a=2, b = 3, and c = 15 are mutually tangent to two other circles. One of them, with bend d = 2, is already given in the
A favorite example of Sarnak’s is the “coins” gasket, so called because three of the four generating circles are in proportion to the sizes of a quarter, nickel and dime, respectively. (Image courtesy of Alex Kontorovich.) 2010 January–February
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Many variations on the Apollonian gasket construction are possible. In this beautiful example, each pore is occupied by three inscribed circles rather than by one. Light blue arcs represent five “curved mirrors.” Reflections in these curved mirrors—known technically as circle inversions—create a kaleidoscopic effect. Every circle in the gasket is generated by repeated inversions of the first six circles through these curved mirrors. (Image courtesy of Jos Leys.)
ting a lightbulb at a point x and asking how many circles illuminated by that lightbulb have radius larger than r. The count will fluctuate, depending on exactly where the bulb is placed. But it fluctuates in a very predictable way. For instance, the count is unchanged if you move the bulb to the location of any of its kaleidoscopic reflections. This property makes the “lightbulb counting function” a very special kind of function, one which is invariant under the same symmetries as the Apollonian gasket itself. It can be broken down into a spectrum of similarly symmetric functions, just as a sound wave can be decomposed into a fundamental frequency and a series of overtones. From this spectrum, you can in theory find out everything you want to know about the lightbulb counting function, including its value at any particular location of the lightbulb. For a musical instrument, the fundamental frequency or lowest overtone is the most important one. Similarly, it turned out that the first symmetric 14
function was all that Kontorovich and Oh needed to figure out what happens to N(r) as r approaches 0. In this way, a simple problem in geometry connects up with some of the most fundamental concepts of modern mathematics. Functions that have a kaleidoscopic set of symmetries are rare and wonderful. Kontorovich calls them “the Holy Grail of number theory.” Such functions were, for instance, used by Andrew Wiles in his proof of Fermat’s Last Theorem. An interesting new kaleidoscope is enough to keep mathematicians happy for years. Gaskets Galore
Kontorovich learned about the Apollonian kaleidoscope from his mentor, Peter Sarnak of Princeton University, who learned about it from Lagarias, who learned about it from Wilks and Mallows. For Sarnak, the Apollonian gasket is wonderful because it has neither too few nor too many mirrors. If there were too few, you would not get
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enough information from the spectral decomposition. If there were too many, then previously known methods, such as the ones Wiles used, would already answer all your questions. Because Apollonian gaskets fall right in the middle, they generate a host of unsolved number-theoretic problems. For example, which numbers actually appear as bends in a given gasket? These numbers must satisfy certain “congruence restrictions.” For example, in the bugeye gasket, the only legal bends have a remainder of 2, 3, 6 or 11 when divided by 12. So far, it seems that every number that satisfies this congruence restriction does indeed appear in the figure somewhere. (The reader may find it amusing to hunt for 2, 3, 6, 11, 14, 15, 18, 23, etc.) “Computation indicates that every number occurs, but we can’t prove that even 1 percent of them actually occur!” says Ron Graham of the University of California at San Diego. For other Apollonian gaskets, such as the “coins” gasket in the fifth figure, there are some absentees—numbers that obey the congruence restrictions but don’t appear in the gasket. Sarnak believes, however, that the number of absentees is always finite, and beyond a certain point any number that obeys the congruence restrictions does appear somewhere in the gasket. At this point, though, he is far from proving this conjecture—the necessary math just doesn’t exist yet. And even if all the problems concerning the classic Apollonian gaskets are solved, there are still gaskets galore for mathematicians to work on. As mentioned before, they could study random Apollonian gaskets. Another modification is the gasket shown in the last figure, where each pore is filled by three circles instead of one. Mallows and Gerhard Guettler have shown that such gaskets behave similarly to the original Apollonian gaskets—if the first six bends are integers, then all the rest of the bends are as well. Ambitious readers might want to work out the “Descartes formula” and the “baby Descartes formula” for these configurations, and investigate whether there are congruence restrictions on the bends. Perhaps you, too, will be inspired to write a poem or paint a tablet in honor of Apollonius’ ingenious legagy. “For me, what’s attractive about Apollonian gaskets is that even my 14-year-old daughter finds them interesting,” says Sarnak. “It’s truly a god-given problem—or perhaps a Greek-given problem.”
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Engineering
Occasional Design Henry Petroski
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he problem of moving and removing large rocks and boulders is millennia old. In its more sophisticated form, the problem has been one of moving large pieces of stone to assemble pyramids, erect obelisks and build cathedrals. In most of these cases, there was little but the power of men, animals and ingenuity to assist in the task. What machines were eventually devised were themselves typically human or animal powered. Most heavy lifting was likely done by direct muscle power involving as large a number of men as necessary, in which case the design of a procedure to determine who lifted when and who pushed and pulled when was critical to the success of the project. Building great monuments, in which there was an enormous amount of repetitive moving of similar pieces of stone, no doubt entailed set operations—and improvements on them as the project progressed. These procedures had to be designed, however, and they most likely evolved by trial and error from ad hoc solutions devised, watched and executed by master builders, engineers and the workers themselves. Learning the Lay of the Roof
I recently witnessed two workmen wrestle with a design problem that was worthy of the Middle Ages, if not of ancient times. As does many a house in Maine, ours has a steeply pitched roof, with a rise of two feet in every run of three. The front portion of the roof is pierced by a chimney, which marks the location inside of the large stone fireplace that divides the living room from the kitchen. The chimney is located about midway up the front slope of the roof, about equidistant between the gutter and the ridge, and is Henry Petroski is Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. Address: Box 90287, Durham, NC 27708-0287 16
An everyday challenge provides lessons in the processes of planning and execution positioned about 15 feet from one gable and 25 from the other. The dimensions of the brick chimney are about two feet by three-and-a-half feet in cross-section, and it projects from about six feet to nine feet above the roof. In other words, the top of the chimney is about at the level of the ridge, but it is about eight feet away from it. The cap on this chimney was made of some unidentified synthetic material, and its underside had begun to deteriorate badly, dropping residue into the flue. Some of the white chalky stuff also found its way to leach down the stone facing of the fireplace. We wanted to replace the bad chimney cap with a new one that would be more resistant to erosion and that would also overhang the chimney more, so that rain was less likely to find its way into the fireplace. We asked a neighbor to recommend someone who could do the job. The mason who came to look at the situation told us that he would have to erect a scaffold to establish a working platform around the chimney. So the job—including erecting and dismantling the scaffolding—might take at least a couple of days to complete, and he quoted a price accordingly. A chimney sweep that we asked said that he did not need scaffolding at all and so could do the job in about an hour. He proposed using a piece of granite
about an inch-and-a-half thick, which meant that it would weigh at least 150 pounds, but he expressed little doubt that he and his helper could handle the job without scaffolding. It was only later that I learned that their full-time jobs were as firemen, so they could be expected to be able to carry the weight of a good size person, in addition to their own fire-fighting gear across a bare roof. Still, removing the old chimney cap, which must have weighed at least 75 pounds, and getting the new one in place all in an hour seemed like an ambitious schedule. On the appointed day, the chimney sweep and his helper arrived in a pickup truck, with a beautiful piece of polished granite in the bed and three ladders on the rack above. One of the ladders was an extension type, and it was leaned against the end of the house closer to the chimney. A second ladder could not be extended, but it had large hooks at one end that enabled it to be secured over the ridge of the roof and thus provide a stairway of sorts up the slope. The first ladder was positioned close to the bottom of the roof and the second close to the gable, leaving it a good 12 feet from the chimney. The chimney sweep climbed up to the ridge of the roof and walked across it toward the chimney. He carried the third ladder, a step ladder, with him and parked it open straddling the peak, at the ready for some future use. Unencumbered by the ladder, he scooted down the slope to the chimney, the top of which was over his head. In a move looking as effortless and as graceful as a gymnast mounting parallel bars, the sweep pulled himself into a kneeling position atop the flat chimney cap and proceeded to hack through and remove the few bolts that had been installed to secure the cap onto the open brickwork. This being done, he dismounted the chimney and called for his helper to join him on the roof. The two men,
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Replacing an aging chimney cap with a 150-pound piece of granite turned out to provide numerous lessons in the timeless nature of ad hoc design. A chimney sweep and his helper proceeded deliberately and with care, yet frequently set conventional modern approaches to worker safety aside in order to complete the bulk of the job within one hour.
standing on the sloped roof on either side of the chimney, and reaching well above their heads, slid the old cap off horizontally and took it to the ridge, where the helper lifted it and carried it over to the long ladder. He placed it across the rails of the ladder and slid it down the slope of the roof as he himself backed down rung by rung ahead of it. When he reached the juncture of the roof ladder with the one against the gable, the sweep came over and held the old chimney cap on the ladder rails while the helper mounted the second ladder. Working together, the two of them repositioned the cap in the crooks of the helper’s arms, which held onto the ladder rails. He backed down the ladder to the ground and carried the old cap over to a tree, against which he leaned it intact. The sweep, who had remained on the roof, called down for a rat-tail brush, which the helper said he called a fox-tail. After some banter, the sweep www.americanscientist.org
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had what he wanted. With the brush in hand, he returned to the chimney and again mounted it, this time kneeling across two of its brick piers to sweep clean the mortar wash that covered the top course of bricks on the chimney proper. The wash was designed to slope outward to direct water away from the flues. He had determined on his first visit that the wash needed to be repaired, and he was preparing the surface before the new cap was installed. Balanced on one hand and two knees across the chimney top, he used the brush vigorously and raised a considerable amount of dust, which made him sneeze. With the dust and loose pieces of old wash cleaned off the bricks, the sweep shouted down that he could see a long crack reaching down into the brickwork of the chimney, which he surmised had allowed water into the fireplace. When he finished brushing the wash surface, he backed down from the chimney top and returned to the
ground. He would apply a new mortar wash only after the new cap was in place, so that while struggling with the heavy new cap he and his helper would be able to have the freedom to grab a handhold anywhere on the chimney. Foreseeing what should not be done is as important to good project design as seeing what should be, and when. Putting Reconnaissance to Work
Removing the old cap had been a practice run of sorts for installing the new, but the weight to be lifted up would be about twice what had been taken down. Furthermore, the men would be working against, rather than with gravity, and the consequences of a misstep would be a broken piece of tabletop-quality granite, or worse. The two men huddled and spoke quietly about how they would get the granite cap up onto the roof, over to the chimney and atop it. They considered possibilities and weighed options, taking into 2010 January–February
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Catherine Petroski
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Access to the roof from the front eaves was ruled out because of the risk of damage to the gutter. The driveway-side gable end proved the best choice.
account the constraints and tradeoffs presented by the design problem and their contemplated solutions. The combination of the pitch of the roof and the location and height of the chimney on it presented a situation that was not exactly like any they had previously encountered, so they knew they would have to proceed with a degree of uncertainty and be prepared to change their plan as conditions demanded. All they could be sure about were their own strength and ingenuity and, perhaps equally importantly, the limits of their strength and ingenuity. Since the polished granite gave little purchase for hands, the sweep directed his helper to get an old rope from the back of the truck. The half-inch diameter rope appeared to be made of nylon and was dirty red, perhaps from years of use on a working boat or in chimney work. The sweep talked quietly to his helper about the rope, seeming to give its provenance and explaining how it had been well stretched and would not give during use. He then inspected the aged rope with the intensity that a diamond cutter might a rough stone. Then the sweep proceeded to tie the rope around the piece of granite as carefully as if he were wrapping a special birthday present. He circled the rope around the slab first one way and then another, tying knots with the practiced speed and precision of a surgeon. The entire length of rope, which must have been 50 feet, was used, and the loose 18
end was tied in multiple knots to finish the package in a bulky bow. The sweep hefted the granite by the rope several times, testing his wrapping and declaring it good. A second rope, one that the sweep had carried in a black nylon pouch up to the roof, had already been secured to the ladder there and thrown over the edge. At first the other end of the rope hung down over the gutter along the front edge of the roof, but that was clearly not the way the granite would be raised, as direct a path as it would provide. (It had already been established that the gutter would be crushed under the weight, and that was why the ground-to-roof ladder had been positioned at the gable. Design is as much about rejecting as selecting alternatives.) The rope was repositioned to hang down over the gable, and the sweep secured a large mountain climber’s carabiner to the crossed ropes on the package of granite. This piece of equipment, through which the hauling rope could move freely, added a new dimension to the personality and experience of the sweep. With the granite secured to the hauling rope, the sweep climbed up to the roof and positioned himself on the roof ladder where it was nearest the top of the ground ladder. The sweep pulled from above and the helper pushed from below, and between them they got the granite cap balanced on the top of that ladder, giving them a chance to rest
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and design their next move. Getting the granite from the one ladder to the other was done by sheer muscle power, with the sweep braced against the bottom rung of the roof ladder and the helper against the top of the groundbased one. When the slab had been transferred successfully, it was centered across the inclined ladder rails and held in place by the helper, who was no doubt aided a bit by whatever friction there was between the old nylon rope and the aluminum ladder. Next, the sweep climbed to the ridge of the roof. From there, he again pulled while the helper pushed the granite up the incline. When the stone package reached the ridge, it again required a maneuver to reposition it for the trek across the roof, which was unaided by any ladder footholds or pulling ropes. The two men had to straddle the ridge and work together, the helper moving backwards and the sweep forward, alternately lifting the granite slab up between them and setting it down at intervals to reposition themselves until they were directly uproof from the chimney. While the helper sat straddling the roof’s peak and holding the piece of granite balanced there like a teeterboard on the ridge, the sweep inched down to the chimney and looked up at it. He held onto the back of the chimney with one hand while he leaned his body down the slope to analyze the task before them one last time. The stepladder that earlier had been parked across the peak of the roof was now positioned against the chimney, not reaching its top but providing a prop or shelf for one end of the granite to be placed on while it would be aligned for the final lift and push into place. The sweep and the helper conferred again, quietly and at length, about how they would lift the heavy granite cap up to the top the chimney. The sweep took one corner of the slab and the helper one side, and the two men lifted its front edge by sheer muscle power onto the waiting stepladder and rested. After a minute, they lifted the edge of the granite onto the brick chimney top and placed it across the four columns of bricks that formed each edge of the crown of the chimney. This movement was a lift as opposed to a slide, for pushing the slab across the brick piers might have opened up cracks in the mortar and damaged the chimney. Besides, the encircling rope had to be contended with.
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Ad Hoc Safety
The installation of the chimney cap is a wonderful illustration of the timelessness of design. Except for the mountain climber’s carabiner, the sweep and his helper used no tools that would not have been available to those who toiled on Egyptian pyramids, Greek and Roman temples, or Gothic cathedrals. Even the aluminum ladders were but a version in modern material of something that could have been familiar to the pyramid engineer Imhotep. The chimney cap installers wore no heavy work gloves, no Kevlar safety harnesses and no plastic hard hats. The helper did not even wear long pants, and his knees were exposed to the gritty surface of the composition shingles. Indeed, the men joked about hoping that www.americanscientist.org
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no representative of the Occupational Safety and Health Administration, the dreaded OSHA, was watching, for they had installed no guard rails and were not tethered to anything. They were, in effect, working in another time. My experience watching the sweep and his helper work not only was evocative of ancient and medieval construction practices, but also was an excellent demonstration of real-time ad hoc design. However, the design problem consisted of more than just moving a piece of granite into place on the chimney top; it also involved the issues of worker and user safety, unorthodox as they may have been. It is well to remember that safety concerns are a relatively recent development. There was likely little concern for ancient workers, save for how an accident might have disrupted work and lowered worker morale. Even as late as the early 20th century, there appears to have been considerable disregard for human worker life, with construction workers wearing little more than soft caps on their heads, providing little protection from projecting beams and falling debris. It was not until the great construction projects of the 1930s, notably those that produced Hoover Dam and the Golden Gate Bridge, that hard hats—at first little more than soft caps covered in hardened tar—were commonly worn and became mandatory on job sites. That the chimney sweep and his helper were casual in their street clothes and dismissive of safety equipment is not to say that they did not follow good practice. At all times they moved deliberately and with a sureness of step. There was never more than one tool in the sweep’s hand at a time, and what was not in his hand was in the hands of his helper. When the sweep sawed off one of the rusty bolts holding the old chimney cap down, he tossed it to the helper, who put it in his pocket. When one of the bolt shanks was stubborn in coming out of the bricks, the sweep used a mallet to persuade it. The piece of metal flew onto the roof and rolled down onto the grass in front of the house. All the time it was rolling, the sweep watched it from his precarious perch. The helper was sent down to retrieve it from the ground, directed by the sweep to move this way and that until it was picked up and placed safely in the helper’s pocket. “That would not be a good thing to hit with a power
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With the cap more or less in place, the rope had to be removed before the final positioning of the cap on the chimney. The helper had remarked when the sweep was tying the multiple knots in it that they would all have to be removed later, but the sweep seemed to take no heed. He had evidently had it in his mind from the beginning that he would sacrifice the dirty red rope, for he did not hesitate when he took a knife from his pocket and sliced the rope in several places. The helper lifted up one side of the slab so that the pieces of rope could be removed and thrown off the roof. (Nothing was ever left underfoot up there.) The sweep then repositioned himself directly behind the chimney, from where he sighted along its sides to gauge the slab’s overhang. He directed the helper where to lift the piece of granite and nudge it left and right. The entire job of removing the old and installing the new cap took less than an hour, as promised. With the new cap in place some 30odd feet in the air, from which no wind or rain would budge it, the sweep returned to the ground to mix a small pail of mortar for forming the new wash. Compared to the cap work, this was not a strenuous task, but it did require some contorting to apply the trowels of mortar to the six distinct openings framed by the brickwork of the chimney, the brick piers and the new granite cap. The job took another half hour, and the sweep and his helper had the truck all packed up and ready to go barely 90 minutes from when they drove down the driveway.
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Once the granite slab was in place, the sweep replaced the wash in the six openings with fresh mortar.
mower,” he shouted down to me on the ground, where I had been watching all the while at a safe distance. Although the granite cap now sitting atop our chimney is a beautiful piece of stone, I am sure that over time it will suffer indignities under the wings of the seagulls, eagles and other birds that fly over our house. Fortunately, I will not be able to see the polished top dulled by the passage of time and birds. Rather, whenever I look up at the chimney or even just watch the smoke rise into it from the fireplace, I am sure I will recall the hour of its installation, not only as a triumph of muscle over gravity but also as a striking example of occasional design. The slab of granite may not cap a pyramid or crown a cathedral, but the process of getting it into place will always symbolize to me the importance of design as procedure as well as of product. Thinking about the problem lifts the thing into place, as much as the idea of the thing pulls the thought about how to do it out of the mind. Thinking about how to accomplish something is in fact the essence of design. The plan is as important as the path; the journey as critical as the goal. When the consequences of a misstep can be fatal, avoiding an unchecked slip along the way can be as important to success as the final push to the summit. As far as understanding the process—as opposed to appreciating the product— of design, the ephemeral journey of a chimney cap is more important than the chimney cap itself. 2010 January–February
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Marginalia
You’ll Never Guess Who Walked In! Pat Shipman
T
he best thing about paleontology is the surprises. No matter how carefully you have analyzed the fossils, no matter how insightful your understanding of the links between anatomical form and function, Mother Nature always comes up with something totally unpredicted. Surprises certainly have been sprung by, and on, the international team of paleoanthropologists and paleontologists that looks for fossils in the remote Aramis region of Ethiopia where the Afar people live. The team is co-led by Berhane Asfaw of the Rift Valley Research Service in Addis Ababa, Ethiopia; Yonas Beyene of the Ministry of Youth, Sports and Culture in Ethiopia;the late J. Desmond Clark, formerly of the University of California, Berkeley; Giday Woldegabriel of the Los Alamos National Laboratory; and Tim White of the University of California, Berkeley. With a nice touch of delicacy, White refers to Clark as “inspiring but no longer making decisions” about the project. On October 2, 2009, the team published in Science their analyses of a hominin (member of the human lineage) called Ardipithecus ramidus. The best representative of the species is a partial female skeleton nicknamed Ardi; she is 4.4 million years old and is certainly astonishing and noteworthy. There are parts of at least 35 other individuals in the collection, in addition to thousands of specimens of plants, invertebrates, fish and assorted nonprimate mammals from the same location. Ardi is the oldest partial skeleton in the hominin lineage at present, but she doesn’t represent a new species. Ardipithecus ramidus has been known since the first research paper about it Pat Shipman is an adjunct professor of anthropology at the Pennsylvania State University. Address: Department of Anthropology, 315 Carpenter Building, Pennsylvania State University, University Park, PA 16801. Email: ________
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Ardi redefines the branch between apes and hominins was published in Nature in 1994 under what might be considered an “alias”: Australopithecus ramidus. The naming of Ardi has had some singular twists and turns. The genus into which the type specimen of Ardipithecus was initially classified was Australopithecus, meaning “southern ape,” a term created in 1925 by Raymond Dart to accommodate a face, jaw and endocast (a natural cast of the braincase) of a young juvenile hominin found in South Africa. The “Taung baby,” as it was nicknamed, was the oldest (about 2.5 million years) and first member of the human lineage to be found in Africa at that point. Skepticism from the scientific establishment at the time of discovery was rife. The hoaxed Piltdown skull, with its large brain (variously estimated between 1,000 and 1,500 cubic centimeters) and seeming antiquity, had been announced in 1911–12 and was still believed to be genuine. Thus the small brain (about 340 cubic centimeters) of the Taung baby was so unexpected that many anthropologists dismissed the fossil as merely an immature, if ancient, ape. Surely our large brain was a fundamental human characteristic extending back to the beginning of our lineage! “Surely”—but not in fact. More than 25 years passed before the anthropological community realized what Dart had recognized from his fossil: Our ancestors had humanlike teeth long before they had a large, humanlike brain. Instead of brain size being the fundamental adaptation that
separated our earliest ancestors from the apes, it was our teeth and, later discoveries showed, our bipedal locomotion. How surprising—and disappointing to those who had prided themselves on their big brains. Since 1925, many different species of Australopithecus have been described and named, including Australopithecus afarensis, the species to which the famous partial skeleton Lucy belongs. All are bipedal hominins, although not necessarily directly ancestral to modern humans. Some apparently ate fruit, whereas others had a more fibrous diet. Some were larger, some smaller, and most species showed a striking difference in body size between males and females (a trait called sexual dimorphism). Some probably made stone tools. They lived in both East and South Africa and may have been more widely spread across the continent between 4.2 and 1.2 million years ago. More Surprises
When Tim White, Gen Suwa of Tokyo University, and Berhane Asfaw described the fossils now known as Ardipithecus ramidus in 1994, they classified the new specimens as Australopithecus. Because the specimens showed some unusual features that differed from other hominins, they defined a new species, Au. ramidus, derived from the Afar word ramid, meaning root. In all biological sciences, naming a new species requires that the scientists fully describe the specimens anatomically and then provide a diagnosis, stating clearly in what ways the type specimen (the object to which the name is formally attached) differs from other known species. At the time, all they had were teeth and jaws, two cranial fragments and a few arm bones—but these pieces were enough to indicate that these 4.4 million-year-old remains were something new. Au. ramidus had
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small canine teeth, like hominins and unlike apes. Small canine teeth that don’t project below (or above) the rest of the tooth row are a key feature separating apes from hominins. Relative to the cheek teeth, the canines of Au. ramidus were still large but were not projecting. Tellingly, the first milk molar—the tooth that falls out in humans at about age five—was small, narrow and very similar to that of a chimpanzee. At the end of the paper, the team made a quiet pronouncement that raised a few eyebrows:
previous paper. More commonly, a new genus is named as part of a detailed reanalysis of alreadyknown material and/or with a thorough description of additional, new fossils. That was not the case here. The major distinction between Australopithecus and Ardipithecus mentioned in the corrigendum is that the dentition of the new genus is less dominated by large cheek teeth than the former. The implied explanation for the need to revise the name at all was a bald statement that a partial skeleton, including a jaw full of teeth and many postcranial bones, had We have taken a conservative been found 50 meters from the position here regarding the type specimen and at the same placement of …[these] fossils stratigraphic level. “Analysis of at the family and genus levthis specimen has begun,” the auels. The major anatomical/bethors deadpanned, “and will prohavioural threshold between vide further features with which known great apes and the Hoto characterize Ardipithecus.” minidae is widely recognized The paleoanthropological to be bipedality and its anacommunity buzzed with excitetomical correlates…. The anment at this revision. First of all, ticipated recovery at Aramis of the note was slipped into a major additional postcranial remains, scientific journal in an unusual particularly those of the lower way. Second, the paper was as limb and hip, may result in reclever a way of saying “We’ve assessment of these fossils at just found something amazthe genus and family level. ing—wait until we tell you!” as All taxonomic assessments are anyone could imagine. subject to revision if new speciFor nearly 15 years, the Aramens show features not previmis team held their peace and ously known, so why include worked fervently on analyzing such a statement at all? I think and understanding their new that the authors had named a specimens, which continued to new species—only a new spepile up. The most spectacular cies, not a new genus—because was the partial skeleton of Ardi. they had limited material, none About the only comment made of which answered the crucial in public about the locomotion question: How did this creature of Ardipithecus was a quip made move? Depending on what the by Tim White at a conference, “If rest of this fossil creature looked you wanted to find something like, they anticipated that they that moved like these things, might need to shift ramidus onto you’d have to go to the bar scene This is the partial skeleton of “Ardi,” a female from the the ape branch of the evolutionin Star Wars.” species Ardipithecus ramidus. The skeleton was found at a ary tree (even though the teeth site called Aramis in Afar, Ethiopia, and has been dated to In October 2009, the team publooked homininlike) or—if its 4.4 million years old. Study of the remains took place over lished their work in yet another pelvis and legs showed evidence nearly 15 years and was punctuated by a number of surpris- unconventional way. They took of two-legged locomotion—into ing discoveries and actions, including the naming of an en- over most of an issue of Science with 11 papers (more than 50 a new hominin genus. Perhaps tirely new hominin genus. (Image courtesy of Tim White.) published pages of text and figthey had one of those nonscientific hunches that the postcranial bones to Ardipithecus ramidus (abbreviated as ures) written by 47 coauthors on Arwould be downright surprising. Ar. ramidus to prevent confusion). The dipithecus’ anatomy, inferred behavior, In less than nine months’ time, an ex- new generic name, Ardipithecus, comes geology, dating, associated animals, traordinary but brief corrigendum ap- from the word for “ground” or “floor” plants and invertebrates, and preserpeared in Nature, written by the same in Afar. I know of no other instance vation. At least as many pages of adauthors. The name of the fossils was in which the naming of a new genus ditional information appeared only in revised from Australopithecus ramidus has been published as a correction to a the supporting online material.
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A comparison of the adult male teeth of modern humans (far left), Ardipithecus (left) and chimpanzees (right) shows that the canine teeth of Ardipithecus are intermediate in size between the other two. The pelvises of both Lucy (Australopithecus afarensis, shown in yellow at far right) and Ardipithecus (in gray, at far right) have broad iliac blades at the top—an adaptation for bipedalism—although Ardi’s ilia are not as expanded as those of Lucy. However, the bottom of Ardipithecus’ pelvis is elongated and apelike, making it unlike any primate pelvis previously known. (Images courtesy of Tim White, Gen Suwa and Science 326:37 2009/AAAS.)
The decision to put all of this work into an issue of Science was influenced by a concern to make the facts accessible. Says White, “With the click of a mouse, Science makes available—to anybody with an Internet connection—a massive amount of material and data. This is effectively monographic treatment, for free, now.” A conventional monograph is planned for the future. In a very real sense, the biggest surprise of all was what Ardipithecus ramidus was like. It was like nothing ever seen before. Ardipithecus may not be the elusive last common ancestor of chimps and humans, but it is far and away the best known of the oldest species. Another species in the genus, Ar. kadabba, lived at least 5.8 million years ago. Together, these new
materials give us stunning insights into what the last common ancestor was like. Practically every paleoanthropologist in the world has drawn a large Y on the blackboard for a class, labeling the lefthand branch “chimpanzees” and the righthand one “modern humans,” and putting an X on the stem just below the divergence and labeling it “last common ancestor.” Based on genetic distances between chimps and humans, that last common ancestor probably lived 6 to 7 million years ago. One of the key points Ardipithecus has revealed is how our thinking has been influenced by the very shape of this common Y diagram. Because we humans have foolishly thought of chimpanzees and other apes as primitive, we have been misled into thinking that the
The remains of a baboon eaten by a cheetah include teeth, cranial fragments, arms complete to the hands, and legs complete to the feet, because cheetahs’ relatively weak jaws cannot break into the stronger and denser bones. Vertebrae, ribs and pelvises are almost completely destroyed. The partial skeleton of Ardi shows the same pattern of preservation, leading to the idea that a catlike carnivore caused her death. (Image courtesy of C. K. Brain.) 22
last common ancestor would somehow be a sort of half-chimp and half-human. Some even fell into the trap of thinking that the last common ancestor was basically a chimp, forgetting that chimpanzees have had as long to evolve since that ancestor as we have. (Students who are a bit confused on this point are always asking, “But if we are descended from the apes, why aren’t there new humans walking out of the jungle today?”) “We have seen the ancestor,” says Tim White succinctly, “and it is not a chimpanzee.” The ancestor also was not Lucy. As the best-known specimen of Australopithecus afarensis—a species that lived between 3.6 and 2.9 million years ago—Lucy became iconic of early hominins. Lucy was an especially petite and diminutive female, standing about 1.1 meters tall, weighing about 29 kilograms, with a reconstructed braincase of about 380 cubic centimeters. When she was discovered in 1974, she seemed incredibly primitive and apelike, so the notion took root in many people’s minds that our earliest ancestors ought to be small, like Lucy. In contrast, Ardi is surprisingly large, which would have had a profound impact on her ecological niche. She stood perhaps 1.2 meters tall, weighed a hefty 50 kilograms, and had a brain size similar to Lucy’s, variously estimated between 300 and 350 cubic centimeters. She was no chimpanzee, but she was within the same size range (both bodily and brainily) as modern chimpanzees and bonobos. Like a chimp, Ardi had long arms, but her fingers were only moderate in length, and her thumbs were intermediate between a chimpanzee’s relatively short thumbs and humans’ relatively long thumbs. Like a chimp, she had a divergent big toe and long toes that could be used to grasp tree branches during climbing.
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Other Comparisons
The arboreal part of Ardi’s locomotion probably closely resembled that of Proconsul, an 18-million-year-old African genus. Proconsul was not a hominin but a primitive or ancestral ape near the divergence between the monkey lineage and the lineage of apes plus humans, and probably an early ancestor of Ardipithecus. Like Ardi, both Proconsul heseloni and a larger species P. nyanzae are known from several partial skeletons. Both had grasping hands and feet, and fore- and hindlimbs roughly equal in length, features that are very important for an animal that moves quadrupedally in trees. Proconsul did not have any strong adaptations for jumping or leaping, so these animals probably moved slowly in the trees. Two big differences between Proconsul and Ardi are body size and sexual dimorphism. P. heseloni females weighed about 8 kilograms, with males as heavy as 10.5 kilograms; P. nyanzae ranged from 27 kilograms for females to 40.5 kilograms for males. In contrast, Ardipithecus was larger, about 50 kilograms, with little apparent malefemale difference in body size. Both Proconsul species and Ardi show many adaptations for slow clambering and quadrupedal locomotion in the trees, and none for knuckle-walking or brachiating. Proconsul is much older but gives clues about the anatomy from which something like Ardipithecus probably evolved. Another striking resemblance between Proconsul and Ardipithecus lies in their preservation. Experiments feeding baboon carcasses to cheetahs carried out by C. K. “Bob” Brain, now retired from the Transvaal Museum in South Africa, showed that cheetahs leave a very particular pattern of bones uneaten. Cheetahs leave behind exactly those parts of the skeleton preserved in the Proconsul skeleton—teeth, cranial fragments, arms complete to the hands and legs complete to the feet—because cheetahs’ relatively weak jaws cannot break into the stronger and denser bones. Vertebrae, ribs and pelvises are almost completely destroyed. On this basis, Alan Walker of Pennsylvania State University suggested that the Proconsul partial skeletons had been eaten by an extinct carnivore analogous to the living cheetah. The partial skeleton of Ardi shows the same pattern of preservation seen www.americanscientist.org
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in cheetah kills and in Proconsul skeletons. Were there cheetahs in Aramis 4.4 million years ago? Not as far as anyone knows. But there were several catlike carnivores in ancient Aramis, including Dinofelis, which is an excellent candidate for Ardi’s killer. Dinofelis is a false sabertoothed cat (its canines were flattened and only moderately long compared to those of true sabertooths) that lived between 5 million and 1.5 million years ago, probably in woodland habitats such as those where Ardipithecus lived. Dinofelis weighed two to three times more than a cheetah, yet its jaws were relatively weak because of the huge gape needed to use its elongated canines effectively. Also, Ardipithecus is about twice as large as a baboon and would have had more substantial bones. Though the research team concluded that most of the hominins and other animals they found were ravaged by hyenas after death, perhaps Ardi herself was attacked by a different carnivore, which accounts for her excellent preservation. When a Chimp Is Not a Chimp
If Ardi was living in woodlands, weighed about as much as a chimp, was about as tall as a chimp, and had arms and legs and hands and feet like a chimp’s, why was she not a chimpanzee? Let me count the ways. First, she doesn’t have apelike teeth. She has humanlike teeth, with small canines that barely project beyond the level of the tooth row. Second, her dental proportions are wrong. In chimps, the front teeth— incisors and canines—dominate the dentition; in humans, the opposite is true. Ardi’s teeth lie somewhere in the middle of the two. Third, the Ardipithecus remains known so far indicate that there is little sexual dimorphism in the species in canine or body size. This is one of the oddest features about Ardipithecus. Strong sexual dimorphism is common among living Old World monkeys and apes, among fossil primates older than Ardipithecus (such as Proconsul), and among hominins in the genus Australopithecus that are more recent than Ardi. If something Proconsul-like evolved into Ardi, and later into Australopithecus, sexual dimorphism was first lost and then regained. Fourth, although her arms and fingers are long like a chimp’s, Ardi’s wrists and hands have no adaptations for brachi-
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ating branch to branch like a young chimpanzee or for knuckle-walking on the ground like an adult chimp. Ardi walked quadrupedally in the trees, placing her hands palm-down on branches and grasping with her big toes. Because she was relatively large, Ardi was probably a slow and careful climber on large branches much of the time. Then there is the most surprising and unchimplike feature of all. According to team member C. Owen Lovejoy of Kent State University, Ardi had a pelvis like no other primate known to science. The upper part of the pelvis in humans forms a large bowl—consisting of the short, curving iliac blades—that cradles the viscera. In a chimp, the flat, long and narrow iliac blades lie behind (or dorsal to) the viscera. In humans, muscles attached to the broad iliac blades balance the body weight over a single pivot leg during bipedal walking. These muscles are differently aligned in apes and cannot serve this function, which is why chimps stagger from side to side when they walk bipedally. Ardi’s upper pelvis was a primary adaptation to bipedal walking on the ground, much closer in shape to Lucy’s pelvis than to a chimp’s. Paradoxically, the lower part of Ardi’s pelvis is very apelike, which is important in climbing vertical trunks with long arms wrapped around the trunk, like an ape or a telephone lineman. “Ardi isn’t a transitional biped,” says Lovejoy. “She’s a biped from a species that’s going to keep its grasping toe and climbing thigh musculature, thank you very much.” He views Ardi’s locomotion and anatomy as mosaics of those in living species. Ardi was clearly not chimp, nor Lucy nor human. Paleoartist Jay Matternes reconstructed her as having fur everywhere but on the center of her face, which protruded more than expected for a hominin. The fur, the long arms and the divergent big toe give Ardi the gestalt of an odd chimp, but that bipedal gait transforms Ardi back into a hominin. The lasting messages from this tourde-force analysis are complex, but the most important lesson of all is simple. Studying the behavior and anatomy of living animals provides us with an understanding of how anatomy links form and function. Genetic comparisons reveal the branching patterns that occurred in evolution and how one living species is related to another. Only the fossils really show us the past. 2010 January–February
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Science Observer A Magic Number? An Australian team says it has figured out the minimum viable population for mammals, reptiles, birds, plants and the rest Imagine how useful it would be if someone calculated the minimum population needed to preserve each threatened organism on Earth, especially in this age of accelerated extinctions. A group of Australian researchers say they have nailed the best figure achievable with the available data: 5,000 adults. That’s right, that many, for mammals, amphibians, insects, plants and the rest. Their goal wasn’t a target for temporary survival. Instead they set the bar much higher, aiming for a census that would allow a species to pursue a standard evolutionary lifespan, which can vary from one to 10 million years. That sort of longevity requires abundance sufficient for a species to thrive despite significant obstacles, including random variation in sex ratios or birth and death rates, natural
catastrophes and habitat decline. It also requires enough genetic variation to allow adequate amounts of beneficial mutations to emerge and spread within a populace. “We have suggested that a major rethink is required on how we assign relative risk to a species,” says conservation biologist Lochran Traill of the University of Adelaide, lead author of a Biological Conservation paper describing the projection. Conservation biologists already have plenty on their minds these days. Many have concluded that if current rates of species loss continue worldwide, Earth will face a mass extinction comparable to the five big extinction events documented in the past. This one would differ, however, because it would be driven by the destructive growth of one species: us.
More than 17,000 of the 47,677 species assessed for vulnerability of extinction are threatened, according to the latest Red List of Threatened Species prepared by the International Union for Conservation of Nature. That includes 21 percent of known mammals, 30 percent of known amphibians, 12 percent of known birds and 70 percent of known plants. The populations of some critically endangered species number in the hundreds, not thousands. In an effort to help guide rescue efforts, Traill and colleagues, who include conservation biologists and a geneticist, have been exploring minimum viable population size over the past few years. Previously they completed a metaanalysis of hundreds of studies considering such estimates and concluded that a minimum head count of more than a few thousand individuals would be needed to achieve a viable population. “We don’t have the time and resources to attend to finding thresholds for all threatened species, thus the need for a generalization that can be implemented across taxa to prevent extinction,” Traill says. In their most recent research they used computer models to simulate
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Researchers have concluded that the same minimum viable population—right around 5,000 adults—is needed to ensure truly longterm survival of all threatened organisms. At least that’s the best estimate given the available data, they say. They advise conservationists to apply that goal to endangered life forms as different as Africa’s black rhinoceros and the South American queen of the Andes plant, which makes seeds just once every 80 years. American Scientist, Volume 98
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“I can’t imagine 5,000 being a meaningful number for both Alabama beach mice and the California condors. They are such different organisms,” Beissinger says. Many variables must be considered when assessing the population needs of a given threatened species, he says. “This issue really has to do with threats more than stochastic demography. Take the same rates of reproduction and survival and put them in a healthy environment and your minimum population would be different than in an environment of excess predation, loss of habitat or effects from invasive species.” But, Beissinger says, Traill’s group is correct for thinking that conservation biologists don’t always have enough empirically based standards to guide conservation efforts or to obtain support for those efforts from policy makers.
That Sinking Feeling Dense development can complicate projections of land subsidence in coastal regions At a time when coastal nations worldwide face threats from sea level rise if climate change advances, scientists are sounding an additional warning. It’s not simply that higher global temperatures could raise seas by expanding ocean water and melting glaciers. What people build, particularly on land with looser soils, could worsen the blow by sinking some coastal areas faster than nature would alone. One project designed to quantify this effect focused on the Fraser River delta in western Canada, home to the coastal city of Vancouver. Using radar measurements taken by satellites, geophysicist Stéphane Mazzotti and colleagues found land subsidence, or sinking, that appears attributable primarily to the weight of what was constructed atop it. “Subsidence due to human activity exceeds the natural rate in heavily built areas,” says Mazzotti, whose findings were published in Geology. Vancouver itself, built on solid substratum, is not at risk. And in undeveloped or lightly developed porwww.americanscientist.org
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tions of the metropolitan area, natural consolidation of upper Holocene sediments is causing subsidence of only 1 to 2 millimeters per year. But in heavily built-up locations outside the city—including the Vancouver International Airport, ferry terminals and industrialized zones—the drop
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what population numbers would be required to achieve long-term persistence for 1,198 different species. A minimum population of 500 could guard against inbreeding, they conclude. But for a shot at truly long-term, evolutionary success, 5,000 is the most parsimonious number, with some species likely to hit the sweet spot with slightly less or slightly more. “The practical implications are simply that we’re not doing enough, and that many existing targets will not suffice,” Traill says, noting that many conservation programs may inadvertently be managing protected populations for extinction by settling for lower population goals. The prospect that one number, give or take a few, would equal the minimum viable population across taxa doesn’t seem likely to Steven Beissinger, a conservation biologist at the University of California at Berkeley.
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“One of the positive things here is that we do need some clear standards. It might not be establishing a required number of individuals. But it could be clearer policy guidelines for acceptable risks and for how many years into the future can we accept a level of risk,” Beissinger says. “Policy people do want that kind of guidance.” Traill sees policy implications in his group’s conclusions. Having a numerical threshold could add more precision to specific conservation efforts, he says, including stabs at reversing the habitat decline or human harvesting that threaten a given species. “We need to restore once-abundant populations to the minimum threshold,” Traill says. “In many cases it will make more economic and conservation sense to abandon hopeless-case species in favor of greater returns elsewhere. —Catherine Clabby was significantly greater: 3 to 8 millimeters per year. Mazzotti, a research scientist with the Geological Survey of Canada, and fellow scientists considered how those changes could interact with two sea level predictions for the end of 2100. One was the mean projected rise, 30 centimeters, by the Intergovernmental Panel on Climate Change. The other, based on glaciology and empirical evidence published in 2006 and 2007 in Science, projects a 100-centimeter increase. Natural subsidence, their data show, could augment climate-change-related sea level rise by 50 to 15 percent under the two scenarios. Anthropogenic
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Vancouver International Airport sits on the Fraser River delta. Scientists have observed that development on the delta has accelerated subsidence, or sinking, of land there. That could have implications for preparations for expected sea level rise on deltas worldwide. 2010 January–February
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subsidence could augment it by 130 to 40 percent, they say. In both cases, subsidence in the delta would need to be considered while preparing for sea level increases, particularly in the design of barriers to protect developed land from seawater. “Municipal planners have recognized that dykes that were built here in the 1960s and 1970s have to be raised to address global sea level rise. Based on our research, it looks like they will have to be raised a bit higher,” Mazzotti says. Scientists have used radar measurements to pinpoint differences in subsidence rates in other delta regions, including New Orleans, which was devastated in 2005 by flooding after Hurricane Katrina. Tim Dixon of the University of Miami and colleagues argued in 2006 in Nature that irregular subsidence could have played a role. His team concluded that most of New Orleans was sinking at an average rate of 6 millimeters a year. But some spots experienced rapid
subsidence in the three years prior to Katrina, as much as 29 millimeters per year. One area with higher subsidence was on the Mississippi River near the Gulf Outlet Canal, where levees failed during peak storm surge. Dixon and collaborators also argued that some levees may have failed after Katrina because subsidence either lowered levees sufficiently to allow overtopping or because weakened substrates promoted levee failure. Previously, other scientists had warned that subsidence in New Orleans was aggravated by flood protection measures that disrupt natural drainage and reduce the deposition of sediments. “Lots of cities are built on deltas,” Dixon says. “Space observations are providing a brand new way to look at the problem.” When it comes to threats of erosion and flooding from sea level rise, municipalities built on deltas will now have a related warning to consider.
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Working in the Vancouver area, Mazzotti and his colleagues compared vertical land movement measurements captured by interferometric synthetic aperture radar between 1992 and 1999 in the greater Vancouver region. Specifically they assembled 350,000 pixels from radar images to track vertical motion changes, with each pixel covering about 13 by 13 meters of land surface. The scientists confirmed and expanded the radar measurements with Global Positioning System (GPS) and land-based surveying tools. They found no evidence that local tectonics or other factors sometimes associated with land sinking could explain the changes in the Fraser River delta. “The specifics may vary depending where you are on a delta. But subsidence is enhanced in areas that are heavily built. That needs to be taken into account,” Mazzotti says.— Catherine Clabby
Geology 2009
This map, produced with measurements by interferometric synthetic aperture radar, displays uplift and subsidence rates in the Fraser River delta, which includes Vancouver. Annual uplift rates during the study period are portrayed with orange hues. Subsidence rates are portrayed in blues. Leveling results are portrayed with filled circles; Global Positioning System results are portrayed with filled squares. 26
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In the News This roundup summarizes some notable recent items about scientific research, selected from news reports compiled in Sigma Xi’s free electronic newsletters Science in the News Daily and Science in the News Weekly. Online: http://sitn.sigmaxi. org and _____________ http://www.ameri__ canscientist.org/sitnweekly __________________
A Little Salt Helps the Leaf Litter Go Down Plants assimilate CO2; when they die, decomposers release it again. But in saltstarved environments such as the Amazon, decomposers don’t keep up, and carbon accumulates in the leaf litter. That might be because, unlike plants, decomposers such as fungi and termites need sodium in their diets. Working in the Peruvian rainforest, a team of ecologists tested that idea by sprinkling 70 small plots with either salt water or stream water. In about two weeks, the salty plots saw a seven-fold increase in termites and lost more than 40 percent of their leaf litter. The authors speculate that increasingly fierce tropical storms could drop more sea salt inland—spurring faster decomposition and carbon release, thus speeding climate change. Kaspari, M., et al. Sodium shortage as a constraint on the carbon cycle in an inland tropical rainforest. Proceedings of the National Academy of Sciences (published online November 2)
Hypnotic Milk Saving morning breast milk to feed the baby in the evening could make for a sleepless night. That’s according a new study that examined daily fluctuations in the composition of human breast milk from 30 moms. The milk contains nucleotides—compounds www.americanscientist.org www.americanscientist.org
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best known as components of DNA, some of which also promote sleep. The most soporific of the nucleotides peaked at dusk and overnight, suggesting that babies who get breast milk at the same time it is produced will have a better sleep at night. Sánchez, C., et al. The possible role of human milk nucleotides as sleep inducers. Nutritional Neuroscience 12:2–8 (February)
Archaeopteryx Demoted It may be an iconic fossil, but it’s not a bird. So say researchers who extracted minute chips of leg bone from Archaeopteryx and other bird-like fossils, and put them under a microscope. Archaeopteryx’s bones were dense and reptilian, rather than air-filled and bird-like. And based on the growth rings in the bones, it took Archaeopteryx more than two years to grow up, compared to just a few weeks or months for modern birds. True avian physiology didn’t show up until 20 million years postArchaeopteryx; that distinction goes to Confuciusornis, a Cretacious specimen now in need of a publicity campaign. Erickson, G. M., et al. Was dinosaurian physiology inherited by birds? Reconciling slow growth in Archaeopteryx. PLoS ONE 4: e7390 (October 9)
Crying With a French Accent There’s an oft-repeated saying that in Paris, incredibly, even the children speak French. Now it turns out the babies cry in French, too. Researchers compared the wails of 60 newborns from Frenchand German-speaking families, and found that their cries mimicked inflections common in their native tongues. Ba-
bies who had heard French from the womb uttered cries of increasing pitch and intensity, whereas German babies produced descending shrieks. It’s well known that fetuses hear the outside world, and newborns recognize aspects of their native language. But this is the earliest that babies have been found to mimic those sounds. Mampe, B., et al. Newborns’ cry melody is shaped by their native language. Current Biology (published online November 5)
Can Bacteria Make You Fat? Genetics, diet, exercise.… Complex factors affect bodyweight, and new studies suggest a role for intestinal microbes, too. In mice that harbor normal human gut bacteria in their intestines, a fatty, sugary diet (as opposed to a low-fat, high-fiber one) drastically altered bacterial metabolism and species composition. In an apparently vicious cycle, the rich diet favored microbes that promote more efficient calorie absorption. And those same microbes, when transferred to other mice, made them gain weight even on a lowfat diet. The results don’t prove that bacteria cause human obesity—but they do suggest it’s an important connection to investigate. Turnbaugh, P. J., et al. The effect of diet on the human gut microbiome: A metagenomic analysis in humanized gnotobiotic mice. Science Translational Medicine 1:6ra14 (November 11)
A Superficial Supernova Astronomers think they’ve spotted a whole new category of supernovae. Revisiting old data from a California telescope, they found a stellar explosion that faded three times faster than a typical su-
pernova. It was also too dim and had an unusual composition of helium with traces of vanadium—but no hydrogen. Those features did, however, fit with the theoretical type .Ia supernova. Theoreticians recently predicted that when a white dwarf star collects helium from a smaller partner star, the helium could eventually detonate in a fast supernova that leaves the underlying star intact. To spot more such fleeting explosions, telescopes may need to revisit the same patch of sky more often. Poznanski, D., et al. An unusually fast-evolving supernova. Science (published online November 5)
Bed Bug Turn-Ons and Turn-Offs Male bed bugs (Cimex lectularius) can’t resist the puffy body of a well-fed, bloodfilled bug, regardless of its sex. If the bloated beauty is a female, her suitor disregards her genital opening and punctures her abdomen to inject his sperm. But if the attractive bug is another male, even he is at risk of an abdominal piercing. Unless, that is, he releases a dose of alarm pheromone—a mixture of compounds previously thought to deter only predators. Researchers found that blocking a male’s pheromone glands left him susceptible to homosexual advances, whereas male-female pairs broke up when exposed to the alarm compounds. The arrangement saves males both wasted time and abdominal injury—and leaves one wondering why females don’t occasionally emit the same “bug off” message. Ryne, C. Homosexual interactions in bed bugs: alarm pheromones as male recognition signals. Animal Behaviour (published online October 24) 2010 January–February 2010 January–February
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9OUR SUPPORT OF 4HE 3IGMA 8I &UND HELPS TO ENSURE THAT 'RANTS IN !ID OF 2ESEARCH ARE AVAILABLE FOR THE NEXT 0ROMISING 3TUDENTS 3INCE 3IGMA 8I 'RANTS IN !ID OF 2ESEARCH HAVE MADE A DIFFERENCE FOR NEARLY UNDERGRADUATE AND GRADU ATE STUDENTS AT A CRUCIAL TIME IN THEIR CAREERS #OMPETITION FOR GRANT FUNDS ESPECIALLY AMONG BEGINNING RESEARCHERS HAS NEVER BEEN MORE INTENSE THAN IT IS TODAY AND OUR ENDOWMENT NEEDS TO GROW SO WE CAN HELP EVEN MORE PROMISING YOUNG RESEARCH STUDENTS 0LEASE HELP CONTINUE 3IGMA 8IS PROUD TRADITION OF SUPPORTING YOUNG PROMISING STUDENTS AT THE OUTSET OF THEIR RESEARCH CAREERS 4HE 3IGMA 8I &UND IS OUR ANNUAL DONATION DRIVE SUPPORTED BY 3OCIETY MEMBERS AND FRIENDS TO DELIVER UNIQUE PROGRAMS DESIGNED TO ENHANCE THE RESEARCH ENTERPRISE 9OUR MAILED OR ONLINE DONATIONS ARE TAX DEDUCTIBLE DEPENDING ON YOUR PERSONAL FILING CHOICE
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RECEIVED A 3IGMA 8I 'RANT IN !ID OF 2ESEARCH IN MY UNDERGRADUATE AND GRADUATE SCHOOL ING 7HILE ) WAS AN UNDERGRADUATE THE GRANT WAS UTILIZED IN EXPERIMENTS THROUGH WHICH ) GAINED AN EXCELLENT BASE FOR LABORATORY WORK 7HEN ) ENTERED GRADUATE SCHOOL THE FUND ING ) RECEIVED FROM 3IGMA 8I WAS VERY BENEFICIAL IN HELPING ME CONDUCT EXPERIMENTS VITAL TO MY PROPOSED THESIS ) WAS ABLE TO PURCHASE RATHER EXPENSIVE ITEMS THAT ARE ESSENTIAL TO MY EXPERIMENTS -Y PROPOSED THESIS CONCENTRATES ON QUANTIFYING RETINAL HEMODYNAMICS IN DIA BETIC ANIMAL MODELS AS WELL AS NORMAL ANIMAL MODELS INJECTED INTRAVITREALLY WITH VASCULAR ENDOTHELIAL GROWTH FACTOR ) AM VERY GRATEFUL IN HAVING RECEIVED THE 3IGMA 8I GRANT BECAUSE IT HAS HELPED MAKE ME A BETTER RESEARCHER AND HELPED SUPPORT MY STUDIES 3ANJA "ENAC
4
HE 3IGMA 8I GRANT AWARDED TO ME IN *ANUARY OF WAS USED TO FUND AIRFARE FOR TRAVEL TO 3OUTH !FRICA SO THAT ) COULD STUDY BOTH THE MODERN AND FOSSIL SMALL MAMMAL COLLECTIONS HELD AT SEVERAL REPOSITORIES INCLUDING THE 4RANSVAAL -USEUM IN 0RETORIA THE .ATIONAL -USEUM IN "LOEMFONTEIN AND THE .ATIONAL -USEUM OF "OTSWANA 4HE FIRSTHAND EXPERIENCE ) GAINED FROM WORKING ON THE FAUNAS FROM SUCH NOTABLE FOSSIL BEARING LOCALITIES AS 3TERKFONTEIN 3WARTKRANS #OOPERS 4AUNG 0LOVERS ,AKE &LORISBAD AND 'CWIHABA IS INVALUABLE !DDITIONALLY THE PROFES SIONAL CONTACTS ) MADE FROM THIS TRIP WILL UNDOUBTEDLY PROVE TO BE OF GREAT USE IN THE FUTURE !LL OF THIS WOULD NOT HAVE BEEN POSSIBLE WITHOUT A 'RANT IN !ID OF 2ESEARCH ) AM SINCERELY GRATEFUL FOR BOTH THE HELP AND SUPPORT PROVIDED TO ME BY 3IGMA 8I 4IMOTHY , #AMPBELL
3
IGMA 8IS 'RANT IN !ID OF 2ESEARCH COVERED MY TRAVEL TO CONDUCT FIELD WORK ON ,AKE -ENDOTA NEAR -ADISON 7ISCONSIN !S PART OF .!3!S !UTONOMOUS 3CIENCE CRAFT %XPERIMENT WE HAD DEVELOPED ALGORITHMS TO PROCESS HYPER SPECTRAL DATA ON BOARD AND CLASSIFY THE PRESENCE OF SNOW ICE WATER LAND CLOUD ETC IN ORDER TO DETECT CHANGES IN THE CRYO SPHERE THE MELTING AWAY OR ONSET OF SNOW COVER SEA ICE FORMATION AND BREAK UP LAKE FREEZE AND THAW -APPING OF SNOW AND ICE COVER ON ,AKE -ENDOTA AND OTHER -ADISON AREA LAKES CONCURRENTLY WITH A SATELLITE OVERPASS ALLOWED ME TO VALIDATE AND QUANTIFY THE PERFORMANCE OF THE ON BOARD CLASSIFICATION ALGORITHM 4HOMAS $OGGETT
)
USED THE FUNDING FROM THE 3IGMA 8I 'RANT IN !ID OF 2ESEARCH TO PURCHASE FIELD SUPPLIES FOR MY PRELIMINARY FIELD SEASON 4HESE INCLUDED MATERIALS FOR TRAPPING LIZARDS AND COLLECTING TISSUE SAMPLES ALONG WITH OTHER MISCELLANEOUS SUPPLIES 4HIS FUNDING ALLOWED ME TO BEGIN TO GATHER DATA AND GAIN EXPERIENCE IN THE FIELD ) AM USING THE PRELIMINARY DATA TO APPLY FOR OTHER FUNDING SOURCES 4HE FUNDS FROM 3IGMA 8I ARE THE CRUCIAL FIRST STEP TOWARDS FINDING ADDITIONAL SUPPORT TO COMPLETE MY PROJECT 4HERE ALWAYS NEEDS TO BE THE FIRST ORGANIZATION TO OFFER SUPPORT TO BEGINNING SCIENTISTS AND ) WILL ALWAYS BE EXTREMELY GRATEFUL TO 3IGMA 8I FOR HELPING TO LAUNCH MY SCIENTIFIC CAREER +EVIN &LOYD
)
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USED THE FUNDING AWARDED BY THE 3IGMA 8I 'RANTS IN !ID OF 2ESEARCH PROGRAM TO STUDY LAKES OF THE ,OFOTEN )SLANDS IN NORTHERN .ORWAY 4HE GRANT HELPED SUPPORT MY FIELD ACTIVI TIES WHICH INCLUDED BATHYMETRIC AND SEISMIC PROFILES OF LAKE BASINS AS WELL AS THE COLLECTION OF SEDIMENT CORES 4HE SEDIMENT CORES ) COLLECTED ARE BEING USED TO STUDY PAST CLIMATE AND EN VIRONMENTAL CHANGE OVER THE PAST YEARS AND ARE THE SUBJECT OF MY DISSERTATION RESEARCH 4HE 'RANTS IN !ID OF 2ESEARCH PROGRAM IS AN EXCELLENT OPPORTUNITY FOR GRADUATE STUDENTS AND HELPED ME TO ACHIEVE MY ACADEMIC GOALS ) WOULD LIKE TO THANK 3IGMA 8I AND ALL OF THOSE WHO HAVE SUPPORTED THIS PROGRAM .ICHOLAS "ALASCIO
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XCLUSIVE MALE PARENTAL CARE IS RELATIVELY RARE IN THE ANIMAL KINGDOM AND TESTING HYPOTHESES ABOUT THE EVOLUTIONARY ORIGIN AND MAINTENANCE OF THIS BEHAVIOR IS OF GREAT INTEREST TO SEXUAL SELECTION AND SEXUAL CONFLICT THEORIES 4HE 3IGMA 8I 'RANTS IN !ID OF 2ESEARCH FUNDING WAS ESSENTIAL IN HELPING ME DEVELOP LABORATORY EXPERIMENTS OF FEMALE MATE CHOICE IN SEA SPIDERS #LASS 0YCNOGONIDA A GROUP OF POORLY KNOWN MARINE ARTHROPODS THAT EXHIBIT MALE PARENTAL CARE OF OFF SPRING 4HE GRANT WAS USED TO PURCHASE BASIC EQUIPMENT FOR SETTING UP MARINE AQUARIA FOR MAINTAIN ING LIVE SPECIMENS OF #ALIFORNIA SEA SPIDERS TO BE USED IN MY DISSERTATION RESEARCH !S AN INTERNA TIONAL STUDENT ) AM RARELY ELIGIBLE FOR GRANTS OR FELLOWSHIPS SO ) AM EXTREMELY THANKFUL TO 3IGMA 8I FOR OPENING OPPORTUNITIES FOR INTERNATIONAL STUDENTS TO IMPROVE THEIR CAREERS &ELIPE "ARRETO
)
RECEIVED A 3IGMA 8I 'RANT IN !ID IN 4HE FUNDING PROVIDED BY THIS AWARD HAS GREATLY CONTRIBUTED TO THE PROGRESS OF MY DISSERTATION PROJECT /NTOGENY OF -ICROSAURS AND )MPLICATIONS FOR -ICROSAUR )NTRA RELATIONSHIPS AND ,ISSAMPHIBIAN /RIGINS -Y STUDY INVOLVES THE DOCUMENTATION OF GROWTH AND DEVELOPMENT IN FIVE MICROSAUR TAXA AS WELL AS AN INVESTIGATION OF POTENTIALLY PHYLOGE NETICALLY INFORMATIVE CHARACTERS WITHIN THE GROUP AS A WHOLE ! MAJOR PART OF THIS RESEARCH UTILIZES (IGH 2ESOLUTION #OMPUTED 4OMOGRAPHY (2#4 SCANS OF MULTIPLE INDIVIDUALS OF ADULT AND JUVENILE 0ANTYLUS CORDATUS 4HIS ADVANCED TECHNOLOGY ALLOWS FOR DIGITAL DISARTICULATION OF THE SKULL WHICH ) USED TO PRODUCE THE FIRST DESCRIPTION OF ISOLATED CRANIAL ELEMENTS IN 0ANTYLUS 7ITHOUT THE FUNDING PROVIDED BY 3IGMA 8I FOR (2#4 THIS PORTION OF MY STUDY WOULD NOT HAVE BEEN POSSIBLE ) AM EXTREMELY GRATEFUL TO 3IGMI 8I AND THE 'RANTS IN !ID PROGRAM *ENNIFER /LORI
3
IGMA 8I FUNDING HAS BEEN CRUCIAL TO MY THESIS BECAUSE IT HAS ALLOWED ME TO DEVELOP A SUC CESSFUL MOLECULAR LABORATORY TECHNIQUE TO IDENTIFY BLOOD MEAL SPECIES COMPOSITION IN THE #HAGAS DISEASE VECTOR 2HODNIUS PALLESCENS 7ITH 3IGMA 8IS SUPPORT ) WAS ABLE TO INITIATE THE WORK THAT HAS ALLOWED ME TO INVESTIGATE HOW SPECIES DIVERSITY AND COMPOSITION IMPACTS #HAGAS DISEASE TRANSMISSION IN A FRAGMENTED FOREST LANDSCAPE OF 0ANAMA ) AM IN THE PROCESS OF FINISHING BLOOD MEAL ANALYSIS FOR THE FIELD SAMPLES ) HAVE COLLECTED ) FEEL VERY FORTUNATE AND HONORED TO BE A RECIPIENT OF THE 3IGMA 8I 'RANTS IN !ID OF 2ESEARCH !WARD 4HANKS AGAIN 3IGMA 8I FOR PLAYING A CRUCIAL ROLE IN THE SUCCESS OF MY DISSERTATION RESEARCH .ICOLE 'OTTDENKER
-
Y 3IGMA 8I 'RANT IN !ID OF 2ESEARCH ALLOWED ME TO SPEND THE SUMMER OF RESEARCHING 0LASMODIUM KNOWLESI MALARIA IN )NDONESIAN "ORNEO FOR A DISSERTATION PILOT PROJECT /VER THE SUMMER ) TOOK FINGER STICK BLOOD SAMPLES FROM RESIDENTS AROUND 'UNUNG 0ALUNG .ATIONAL 0ARK TO TEST FOR INFECTION WITH 0 KNOWLESI A POTENTIALLY FATAL KIND OF MALARIA PREVIOUSLY FOUND IN -ALAYSIAN "ORNEO BUT NEVER FOUND BEFORE IN )NDONESIA 4HIS FORM OF MALARIA HAS LONG BEEN KNOWN TO INFECT CERTAIN NON HUMAN PRIMATES BUT ONLY RECENTLY HAS BEEN DISCOVERED TO INFECT HUMANS AS WELL !FTER ESTABLISHING THE PREVALENCE OF THIS FORM OF MALARIA IN THE AREA ) INTEND TO STUDY THE TRANSMISSION CYCLES OF THE PARASITE BETWEEN THE PEOPLE LIVING AT THE FORESTS EDGE AND THE PRIMATES LIVING IN THE FOREST ) ALSO WILL STUDY THE EFFECT OF THE INCREASING PALM OIL PLANTATIONS AT THE FORESTS EDGE WHICH MAY FORM GOOD BREEDING SITES FOR THE MOSQUITOES PRIMARILY RESPONSIBLE FOR HUMAN INFECTION WITH 0 KNOWLESI 4HESE STUDIES MAY ULTIMATELY HELP IDENTIFY RELATIVELY CHEAP LOW TECH WAYS TO REDUCE THE PREVALENCE OF 0 KNOWLESI IN THE PEOPLE OF THE AREA 2YAN "OYKO 4O LEARN MORE ABOUT 3IGMA 8IS 'RANTS IN !ID OF 2ESEARCH PROGRAM VISIT WWWSIGMAXIORG')!2 _________________ )NTERESTED IN CREATING A .AMED ')!2 AWARD #ONTACT DEVELOPMENT SIGMAXIORG OR ___________________
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Assessing Risks from Bisphenol A Evaluating human health risks from endocrine disruptors such as BPA is difficult, but animal studies suggest trouble is afoot Heather Patisaul he industrialized world produces an immense amount of plastic, more than 45 billion kilograms annually in the United States alone. But what is it made of, and is it all safe? Some reusable water bottles sold in Wal-Mart and other retail stores in the United States now display stickers proudly marketing themselves as “BPA-free.” The labeling results from consumer concern over scientific evidence that bisphenol A (BPA), a common ingredient in many hard plastics, may be harmful to the human reproductive system because it interferes with hormones. The plastics industry and the U.S. Food and Drug Administration (FDA) say BPA is not dangerous at the levels people are currently exposed to. In contrast, in September of 2008, the U.S. National Toxicology Program (NTP) concluded that there is “some concern” for adverse effects on the “brain, behavior and prostate gland in fetuses, infants, and children.” This concern prompted members of Congress to pressure the FDA to take another look, a process that is now underway. Inconsistent messages about BPA safety have generated considerable public rancor, highlighting how huHeather Patisaul is an assistant professor of biology at North Carolina State University who specializes in neuroendocrinology and endocrine-disruption research. She is also a science communication fellow for Environmental Health News. She is a former investigator and post-doctoral researcher at the Hamner Institutes for Health Sciences—known then as CIIT or The Chemical Industry Institute of Toxicology—in Research Triangle Park, NC. Patisaul received her Ph.D. from Emory University in 2001. Address: Department of Biology, North Carolina State University, 127 David Clark Labs, Raleigh, NC 27695. Internet: _____ heather_
[email protected] ___________ 30
man risk assessment of BPA (and compounds like it) is both uncoordinated and controversial. Consensus regarding BPA’s safety has evaded U.S. health agencies for multiple reasons. Most pressing is the lack of clear guidelines for how much or what type of scientific evidence is needed to judge risks from hormone-disrupting compounds such as BPA. It would be unethical to directly assess those risks in people through controlled, double-blinded exposure experiments. At the same time, there are uncertainties about when exposure data from animal studies are relevant to human health. In a global environment where BPA production and exposure have grown rapidly, there is a pressing need to overcome these challenges. That is especially true because BPA is only one of thousands of chemicals thought to possibly have unintended effects on reproductive health. In the U.S., BPA ranks in the top 2 percent of high-production-volume chemicals. BPA is a monomer that makes polycarbonate plastics harder and more resilient. Polycarbonate plastics are typically clear and often designated by a “7” within their triangular recycle symbols. BPA is also found in the epoxy resins that line the inside of metallic cans (such as soup and soda cans) and water storage tanks. BPA is also in thousands of other products, including compact discs, eyeglasses, thermal paper, polycarbonate water pipes, medical devices and dental sealants. Consumption is thought to be the most common route of human exposure because BPA readily leaches from food containers into their contents, especially when its heated, including in a microwave. Centers for Disease Control and Prevention (CDC) scien-
tists have estimated that more than 92 percent of Americans have BPA in their bodies, and the highest levels are typically found in children. BPA is an endocrine disruptor, which the Environmental Protection Agency (EPA) defines as “an exogenous chemical substance or mixture that alters the structure or function(s) of the endocrine system and causes adverse effects” in individuals, their offspring or populations. Hormones have many modes of action, including the ability to initiate or suppress gene transcription. Endocrine disruptors interfere with those geneticlevel processes. The timing of exposure is critical because vulnerability changes over a lifespan. In an adult, where sexspecific physiology and behaviors have matured and function properly, interference with hormone action is likely reversible once exposure ends. This is not thought to be the case in the developing fetus or young child. Therefore, fetuses and infants are the groups most at risk for adverse effects from an endocrine disruptor such as BPA. Over the course of development, hormones actually help shape the vertebrate brain and reproductive organs that allow sex-specific physiology and behaviors to emerge. Much of this hapFigure 1. A factory worker in England lifts a reusable water container manufactured, in part, with bisphenol A (BPA), a chemical used to make polycarbonate plastics and epoxy resins. BPA is an endocrine disruptor, meaning it is capable of interfering with normal hormone functioning in organisms. Evidence is mounting that BPA exposure can disrupt normal reproductive-system development and functioning in laboratory animals. There is a pressing need to overcome challenges to assessing the true risks that this compound—and the many others like it—pose for people.
Peter Ginter/Science Faction/Corbis
T
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Figure 2. Scientists are scrutinizing health risks from BPA so carefully because the compound is abundant. Production in the United States alone increased from 7 million kilograms in the early 1990s to 1 billion kilograms in 2004. BPA is found in food storage containers, food and drink can liners, dental care materials and other products. The federal National Toxicology Program says people are exposed to BPA most frequently through their diet. The highest estimated daily intake occurs in infants and children. BHF ZFBST
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Figure 3. The U.S. Centers for Disease Control and Prevention in 2008 estimated that more than 90 percent of Americans have detectable levels of BPA in their bodies, based on urine sample analysis of a representative group of 2,517 people. Children between the ages of 6 and 11 years had higher urinary levels than adults. Levels varied with household incomes too. The findings were published originally in Environmental Health Perspectives. 32
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pens in discrete developmental windows that span gestation through the postnatal period and, to some degree, into adolescence. Disruption of this developmental progression can permanently alter the organization of sexually dimorphic neuroendocrine circuits in the brain, the cellular composition of reproductive organs, the timing of puberty, the development of sex-typical behaviors and, ultimately, the capacity to reproduce. BPA exposure, even at levels humans are likely exposed to, appears to produce every one of these effects in laboratory rats and mice. But does it produce similar reproductive disorders in humans? The reproductive effects found in laboratory rodents mirror some disturbing human health trends in industrialized nations. For example, an analysis of more than 100 research studies concluded that sperm counts in the United States and Europe appear to have declined by roughly half over the past 50 years. Researchers in Denmark now estimate that more than 10 percent of men in that country have sperm counts in the infertile range and up to 30 percent in the subfertile range. Rates of testicular cancer appear to be increasing. There are indications that female fecundity is declining, even among young women, although the rate and degree have been difficult to quantify. Median ages at menarche, first breast development and sexual precocity are dropping, especially among minority populations in the U.S. Similar trends have been noted in Europe and among children adopted from developing countries by parents in industrialized settings. The cause is likely complex and multifacet ed, but the rapidity of the changes suggests an environmental component. Whether BPA might be involved hinges on whether effects observed in rodents reasonably predict what could be happening in humans.
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The BPA Puzzle BPA has more than one mode of action, but it is primarily recognized to be an estrogen mimic. Effects from endocrine disruption by an estrogen mimic in the developing fetus are likely subtle and not readily apparent at birth. The best example of this in humans is the tragic case of diethylstilbestrol (DES), a synthetic estrogen prescribed to upwards of 10 million women between 1938 and 1971. DES incorrectly was thought to reduce the risk of miscarriage. Instead,
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tive physiology and behavior at doses equivalent or below the current LOAEL and, even more disturbingly, below the reference dose for humans. One of the most frequently observed consequences of low-dose exposure during development is the premature loss of a regular estrous cycle, an effect that produces an abbreviated period of fertility. We found that female rats exposed to the reference dose of 50 micrograms of BPA per kilogram for only the first four days of life developed an irregular estrous cycle as young as two and a half months of age. Rats normally remain fertile for upwards of a year. Similar effects have been reported in both rats and mice at equivalent or even lower doses. Another well-documented effect in female rodents, observed by us and others, is disruption of pubertal timing. The effect is dose dependent: Doses near the 50-micrograms-per-kilogram reference dose advance pubertal onset, whereas higher doses delay it. Disruption of puberty is of particular interest for two primary reasons. First, it appears to be induced by lower, rather than higher, BPA doses, the mechanism for which is not well understood. Second, there is increasing evidence that puberty in girls is occurring earlier, especially in industrialized countries. Girls with advanced puberty outnumber boys with a similar condition 10 to 1, with nearly half of all African-American girls and approximately 15 percent of Caucasian girls showing clear signs of puberty, particularly breast development, by age nine. The timing of pubertal onset in humans is likely impacted by a suite of factors, including nutritional status, stress, socioeconomic status and genetics. But it has been hypothesized that exposure to estrogen-like compounds, including BPA, may partially explain this phenomenon. Disruption of pubertal timing and the capacity to maintain a regular estrous cycle could result from developmental effects in the brain, the reproductive tract or both. Reproductive health ultimately depends on the proper organization and function of the hypothalamic-pituitary-gonadal (HPG) axis, a neuroendocrine system involving the hypothalamus; the pituitary gland, lying just beneath the brain; and the gonads (ovaries in females, testes in males). Hormones play a vital role in the sex-specific organization of all three components, so gestational exposure to endocrine disruptors has the potential
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many children whose mothers took DES during pregnancy, both male and female, developed reproductive health problems as adults. Decades of DES use passed before indications of adverse effects were detected. A pair of physicians noted that DES daughters were more likely than unexposed women to develop an extremely rare form of vaginal clear cell carcinoma. Subsequently, malformations of the uterus, increased risk of testicular cancer, infertility and other reproductive health problems were also ascribed to fetal DES exposure. With DES, the severity of health effects corresponds to the timing and level of in utero exposure, illustrating the importance of tracking critical windows of exposure when attempting to predict potential consequences from human exposure to endocrine disruptors. Important differences exist between DES and BPA. Most significantly, BPA is not as potent. The binding affinity of BPA for the two primary forms of estrogen receptor (ER and ER) is approximately 10,000-fold weaker than that of estradiol, a natural estrogenic hormone, or of DES. To put this in context, the binding affinity of DDT and BPA are in a similar range. Also, human exposure to BPA is estimated to be relatively low—lower than the DES doses pregnant women received. Published estimates of human exposure to BPA are somewhat variable but generally fall in the range of 1 to 15 micrograms per kilogram of body weight per day or less, with infants and children on the upper end of that range and adults on the lower. Blood and urinary levels increase following the consumption of beverages from BPA-containing polycarbonate bottles, indicating that exposure rises and falls as people use products containing BPA. The EPA has set a “reference dose” of 50 micrograms per kilogram of body weight. This dose is considered safe for humans, even with daily exposure over a lifetime. It is based on the Lowest Observed Adverse Effect Level (LOAEL) of 50 milligrams per kilogram of body weight per day, the lowest dose at which any adverse effects should be observed in laboratory animals. BPA’s low estrogenic potency combined with the low level of human exposure have traditionally been interpreted to indicate little to no risk of human health effects from BPA exposure. Yet there is growing evidence from multiple laboratories, including ours, that BPA can alter rodent reproduc-
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American Scientist
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Figure 4. In rodents, exposure to BPA or the potent estrogen estradiol benzoate during development can lead to changes in reproductive functioning. In females, this can mean earlier pubertal onset or the premature loss of the ovulatory cycle. Puberty in laboratory animals is advanced at lower doses of BPA but unaffected or delayed at higher doses. The mechanism for this is unclear.
to induce effects anywhere within the axis. Our laboratory’s work has focused primarily on the brain. Chasing Meaningful Effects Within the brain, volumes of sexually dimorphic nuclei in the hypothalamus are commonly used as a biomarker to study the neurodevelopmental impacts of endocrine disruptors. In the rodent brain, one of the most frequently studied regions is the sexually dimorphic nucleus of the preoptic area, known as the SDN, which is considerably larger in males than in females. The SDN is sensitive to steroid hormones from gestational day 18 until four days after birth. Following this critical period, a phase of sexually dimorphic apoptosis, or programmed cell death, begins, ending on postnatal 2010 January–February
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high bisphenol A
control antral follicle
developing follicle
corpus luteum
estradiol benzoate
low bisphenol A
Figure 5. Above are images of adult rat ovaries in animals used in a study of neonatal exposure to BPA. The unexposed control developed normally. Neonatal female rats exposed to estradiol benzoate, a potent estrogen, had very small ovaries with no clear signs of active follicular development or ovulation. Ovaries from rats exposed to BPA were characterized by an increased number of antral-like follicles in their ovaries, only some of which contained oocytes. These structures resembled ovarian cysts. BPA-exposed animals had lower numbers of corpora lutea, structures essential for establishing and maintaining pregnancy. In one study, ovaries from the high dose group, 50 milligrams BPA per kilogram body weight, displayed more abnormalities than animals exposed to a lower dose of 50 micrograms BPA per kilogram body weight. Other laboratories have reported similar abnormalities at lower doses.
ly negative and somewhat inconsistent results. For example, we determined that administration of the relatively high dose of 500 micrograms BPA over two days, beginning the day after birth, failed to alter SDN volume in male rats. Other studies, using higher and lower doses of BPA and exposure periods spanning both the gestational and postnatal periods, have also largeF
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ly failed to find evidence for BPA effects on SDN volume. Although these results are initially reassuring, we’ve concluded that using the SDN as a biomarker for endocrine disruption is problematic for several reasons. First, it appears to be relatively resistant to most endocrine disruptors, particularly in the Sprague Dawley rat. In addition, the functional role of the SDN is not readily apparent. It has long been accepted to play a role in male sexual behavior, but its role appears to be minimal. A final caveat is that humans have no clear SDN, so it is not entirely evident which reproductive health effects might be predicted by disruption of this region in rodents. It may be a useful region, however, to demonstrate mode of action. For example, we have found that BPA significantly increases the number of SDN cells containing calbindin-D28k, a protein thought to protect against apoptosis. This effect is consistent with the hypothesis that BPA acts as an estrogen mimic. Collectively these data show that, although the SDN is a popular marker for endocrine disruption, it may not actually be a very good one. Another sexually dimorphic brain region that we and others have examined is the anteroventral periventricular nucleus (AVPV). In contrast to the SDN, the AVPV is larger in females than in males, and neonatal estrogen exposure induces, rather than prevents, the apoptosis that produces the size difference. Also, the functional significance of the AVPV is very well understood. The AVPV is essential for the coordination of the hormonal and environmental signals that regulate the secretion of gonadotropin releasing hormone (GnRH). In normal adult females, a “surge” of GnRH, elicited though positive feed-
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day 12. Early exposure to estrogen, derived from the conversion of testicular androgens, protects the male SDN from apoptosis. In females, because estrogen levels are low during this period, apoptosis in the SDN progresses unabated, resulting in a smaller SDN. Attempts to evaluate the impact of BPA exposure on SDN volume, in both males and females, have yielded large-
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Figure 6. In the image at left, cells containing the protein calbindin (CALB) are clearly visible and sharply define the borders of the sexually dimorphic nucleus of the preoptic area (SDN). The SDN is normally larger in males than in females so, as expected, the volume of the CALB-SDN was significantly smaller in ovariectomized (OVX) females compared to unexposed control males. Neonatal exposure to BPA did not significantly affect the volume of the CALB-SDN but significantly increased, and thus hypermasculinized, the number of CALB cells in the SDN compared to the untreated males. This study showed that exposure to BPA could affect the content of a brain region without changing its overall size. 34
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back by the preovulatory rise of estradiol, induces the release of luteinizing hormone and, consequently, ovulation. In male rodents, neonatal estrogen, aromatized from testicular androgen, acts to defeminize the male AVPV such that GnRH neurons are no longer capable of responding to elevated estrogen levels with a surge of GnRH. Similarly, neonatal estrogen administration can defeminize the female AVPV, resulting in the inability to generate a GnRH surge in adulthood. The clearly defined functional significance of this region, combined with its sensitivity to estrogen during a discrete neonatal window, makes it a potentially ideal target for examining the impact of BPA exposure on sex-specific brain organization. We found that administering the relatively high dose of 500 micrograms of BPA to male rats for only two days within this critical neonatal window of estrogen sensitivity did not affect the overall size of the AVPV. It did, however, result in a more female-typical number of dopaminergic neurons within the AVPV. Beverly Rubin of Tufts University subsequently reported finding male-typical numbers of dopaminergic neurons in the AVPV of female mice exposed from gestation through lactation to lower, environmentally relevant doses but did not look at AVPV volume. Together, these studies suggest that the AVPV is likely more sensitive to endocrine disruption than the SDN. They also support the hypothesis that BPA exposure may disrupt sexual differentiation of the brain in general, and within the AVPV specifically. Another group of neurons of interest within the AVPV is the newly discovered kisspeptin neurons. It is now apparent that the kiss1 gene, which codes for a family of proteins called kissFigure 7. This diagram depicts the hypothalamic-pituitary-gonadal (HPG) axis in the rat. The human HPG axis is nearly identical. The location and composition of some brain regions differ in humans. Also, in rats, estrogen masculinizes the brain. In humans, it appears that androgens accomplish that task. BPA, which chemically resembles estrogen, interferes with the development and function of the HPG axis in rodents. When it does, it disrupts the normal development of the reproductive system. Areas in red and green identify locations where researchers have observed anatomical changes in rats after BPA exposure. Those in red, including the hypothalamic brain regions, are components of the HPG axis. www.americanscientist.org
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peptins (KISS), is vital for the regulation of GnRH secretion in many species, including humans. It appears to be essential for the timing of both pubertal onset and ovulation. People with a mutated form of the kisspeptin receptor never enter puberty and remain hypogonadal throughout life. In the rat, there are two
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major populations of KISS neurons, one in the AVPV and one in the arcuate nucleus, another sexually dimorphic nucleus in the hypothalamus. The density of KISS neurons appears only to be sexually dimorphic in the AVPV, with females having significantly more KISS neurons than males. This population is
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thought to be critical for initiating the surge of GnRH that precedes ovulation. To establish whether neonatal exposure to BPA could disrupt development of the AVPV KISS system, we injected rats with either 50 milligrams or 50 micrograms of BPA per kilogram daily for four days starting at birth. In rats, this is when the KISS system is most sensitive to estrogen. (In humans, this sensitivity window likely occurs in the early part of pregnancy’s second trimester.) In female rats, only the higher dose of BPA affected AVPV KISS levels. No effect was observed in the males. Interestingly, however, we also found a slight, but statistically significant, reduction of KISS in the arcuate nucleus of females exposed to the higher BPA dose. In contrast to the AVPV, the number of KISS neurons in the arcuate nucleus is not thought to be sexually dimorphic, and this population appears to be important for the regulation of steroid negative (rather than positive) feedback. Collectively these findings are important because they demonstrate that permanent, sex-specific effects within the brain are possible at exposure levels approximately equivalent to the LOAEL. By definition, no effects should be observable at or below this level.
Answering the Critics Our work has been criticized because the animals in our studies were exposed by injection rather than by mouth. Humans are primarily exposed orally so there is concern that injection is not an appropriate exposure route for animal studies. This argument, although logical on its face, is not so straightforward. Injection bypasses metabolism, a process that conjugates most BPA and renders it inactive. The plastics industry has long argued that BPA is rapidly metabolized and excreted in humans, and is therefore not a threat. It has also been posited that, because non-oral administration, such as injection, bypasses metabolism, it presumably results in higher circulating levels of estrogenically active, or unconjugated, BPA. There are two significant problems with these assumptions. First, at least one study comparing oral administration and injection in neonatal rodents found no qualitative difference in the circulating levels of unconjugated BPA or its metabolites. Second, rodents and humans do not metabolize BPA the same way. In humans, the majority of the metabolites end up in the urine while in rats they are excreted in the feces. In addition, oral dosing is often stressful for animals, and does not adequately repli-
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cate exposure through dental sealants or implanted medical devices. Finally, even if most BPA is conjugated in adult humans, this may not be true for children or infants because their gastrointestinal systems are not fully mature. Considerable scientific debate persists regarding the capacity for immature rodents and humans to adequately metabolize BPA. Our rodent brain research has also been challenged because of key anatomical differences between the rodent and human brains. Most significantly, in humans and other primates it appears that androgens, rather than estrogens, are primarily responsible for masculinizing the hypothalamus. Therefore, disruption of AVPV organization in rats, the argument goes, may not predict a concomitant effect in humans. Disruption within the rat AVPV does, however, clearly show that BPA has the potential to interact with developmental estrogen pathways, an effect that may impact aspects of human brain development. Another caveat is that humans have no AVPV. Humans do have kisspeptin neurons and discrete brain regions that coordinate GnRH release. So studying this neuronal population in rats will likely be informative for BPA’s effects on humans as well. These caveats again highlight
Inconsistent Responses to Bisphenol A over Time The usefulness of bisphenol A (BPA) in plastic manufacturing has long been clear. What’s unclear is whether exposure to BPA poses risks to people. Government bodies in the United States and elsewhere respond differently to the same scientific evidence. 1891: Chemist Aleksandr Dianin in Saint Petersburg, Russia, synthesizes BPA. 1953: Polycarbonate plastic is devel-
oped both at Bayer Hermann Schnell and General Electric. 1957: BPA enters commercial production
kilogram of body weight. That standard remains today. 1996: The Food and Drug Administra-
tion (FDA) concludes that adults are exposed to approximately 11 micrograms of BPA per day and infants are exposed to 7 micrograms per day. 1997: Fred vom Saal of the University of Missouri-Columbia publishes the first animal study showing adverse reproductive effects at doses equal to or lower than those known in humans. The FDA finds BPA in infant formula, demonstrating that BPA can leach into food.
and is incorporated in epoxy resins. 1999: Consumers Union finds that BPA 1982: The National Toxicology Program
(NTP) establishes a lowest observed adverse effect level (LOAEL) of 50 milligrams per kilogram of body weight or 1000 parts per million. 1988: The Environmental Protection Agency (EPA) sets its safe dose, the reference dose, at 50 micrograms BPA per 36
safe. Many scientists are critical, noting that some low-dose animal studies were not considered.
can leach from baby bottles, especially when heated. 1999: FDA asserts that BPA is safe because human doses are too low to cause adverse effects. 2006: A NTP advisory panel draft report generally concludes that BPA is
2007: The NTP advisory panel’s final report finds “some concern” about the neural and behavioral impacts of fetal exposure to BPA. Congress asks the FDA to clarify its BPA position. 2008: NTP concludes that BPA may
pose a threat to humans. Canada announces plans to ban BPA from baby bottles. Legislation emerges in ten U.S. states to limit or ban BPA in products. Playtex, Nalgene and other manufacturers plan to stop using BPA. Wal-Mart starts to phase out BPAcontaining bottles. FDA draft assessment reasserts the position that BPA is safe. The Journal of the American Medical Association publishes the first study observing a correlation between BPA exposure and human disease, such as heart ailments, diabetes and liver toxicity. Amid growing pressure from Congress, the media, some scientists,
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the difficulties in translating results from rodents to humans but do not discount the importance of animal work by us or others. It is important to keep in mind that the developmental period in which steroid-sensitive organization occurs in humans happens largely during gestation rather than in the first few days of neonatal life. Thus, when exposing rats neonatally it is imperative to select BPA doses that correspond to prenatal exposure levels in humans. It is clear that BPA exposure can disrupt pubertal timing and compromise the capacity to maintain a regular ovulatory cycle in rodents. It is likely that these defects result from the abnormal organization of the hypothalamicpituitary-gonadal axis, the crucial neuroendocrine pathway that regulates reproductive function. Our work has found evidence for effects in the brain, but growing evidence suggests that the entire axis is vulnerable. For example, National Institutes of Health researchers have identified numerous reproductive-tract abnormalities in aged female mice exposed to BPA in utero at doses as low as 0.1 microgram per kilogram. We have observed cyst-like structures in rats neonatally exposed to 50 milligrams BPA per kilogram. Increased
numbers of blood-filled ovarian bursae (indicative of advanced reproductive age), abnormal numbers of antral follicles, irregular chromosomes and decreased corpora lutea (tissues vital to a fertilized ovum) have also been observed by a number of research groups following exposure to BPA during development. BPA has also been found to induce apoptosis and cell arrest in cultured ovarian granulosa cells, suggesting that BPA may also impact the adult ovary. These studies indicate that the ovary may be a particularly sensitive target of BPA. Other laboratories have observed that gestational exposure to BPA at doses below the reference dose can result in numerous uterine abnormalities (including many that commonly precede carcinogenesis), alter mammary gland development, diminish the capacity to maintain pregnancy and induce abnormalities in the prostate. It is also important to note that a handful of studies have found no effects from BPA at all. The most recent of these, published by EPA researchers in October of 2009, found no changes in the timing of pubertal onset, sexual behavior or fecundity among female rats after exposure to BPA during gestation and lactation. Inconsistent re-
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sults continue to plague the field and make human risk assessment extraordinarily difficult. It is not readily clear why some effects are not easily replicated by other groups. Resolving how to interpret evidence from laboratory animals, and soon, is pivotal because BPA is not the only endocrine disruptor people are exposed to. Thousands of other compounds are also suspected of having similar properties, including some plasticizers, flameretardants, pesticides and anti-microbials. On top of that, it’s important to consider the combined effect of exposure to multiple endocrine disruptors. A research group at Washington State University recently reported that they could not replicate previously published BPA effects in the mouse ovary. They ultimately determined that effects were only observed in mice maintained on soy-rich diets, leading the authors to hypothesize that diet, along with methodological differences, could explain why the literature surrounding “low dose” effects of BPA is fragmented and inconsistent. The concept of mixture effects is an evolving area of endocrine-disruption research. It could have profound implications for human health if these compounds are found to be more likely
and a few state governments, the FDA plans a new risk assessment.
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2009: Sonoco (a BPA manufacturer) announces it will stop selling the chemical for use in children’s food containers. Minnesota is the first state to ban BPA from baby bottles and sippy cups. Similar laws pass in Chicago and Connecticut. The Endocrine Society calls for increased scrutiny and centralized regulation of suspected endocrine disruptors, including BPA. The American Medical Association does the same. New language in the Food Safety and Enhancement Act requires the FDA to finalize its position on the safety of BPA in food containers by December 31, 2009. The EPA announces that it will review BPA’s health effects. The Obama Administration asks Congress to draft legislation allowing greater scrutiny and regulation of chemicals, including BPA. Consumers Union finds that BPA leaches from cans, including some cans marked BPA-free.
Environmentalists, including mothers holding babies, gathered outside Massachusetts Governor Deval Patrick’s office in March 2009. They were there to deliver more than 8,000 messages from consumers urging Patrick and the state’s Department of Public Health to ban the use of BPA in children’s products or, at a minimum, to issue a health advisory. Such consumer activism is one response to concern over scientific evidence that BPA alters normal reproductive development in laboratory animals. 2010 January–February
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to produce significant health effects collectively rather than individually. Another sobering possibility is that endocrine disruptors could have transgenerational effects. For example, there is emerging concern that the children of DES daughters (referred to as DES granddaughters) might also develop reproductive problems. For these girls, their exposure occurred while they were only germ cells in their mothers’ developing ovaries, within the wombs of their grandmothers. This concern arose from laboratory data indicating that the offspring of female mice exposed in utero were more likely than unexposed control animals to develop reproductive-tract lesions. There are not enough human data to indicate a trend for deleterious effects in DES granddaughters. But this cohort is still quite young. Continued monitoring of these women as they age will be required. The precise mechanisms through which endocrine-disrupting effects transmit to subsequent generations are not well understood, but emerging evidence indicates that epigenetic mechanisms might be primary. Epigenetic inheritance involves changes in gene expression patterns without changes in gene sequence. Such effects include DNA methylation and histone modifications. If epigenetic modifications occur within the germ cells, transmission to subsequent generations is possible. Randy Jirtle at Duke University found evidence in agouti mice that suggests that BPA has the potential to induce epigenetic effects. Other compounds, including polychlorinated biphenyls (PCBs) and the fungicide vinclozolin, have been shown to produce transgenerational effects, perhaps through epigenetic mechanisms. This newly discovered and evolving area of research has once again challenged toxicologists and introduced a novel method by which endocrine disruptors and other toxicants may affect vertebrate physiology and behavior.
Figure 9. While the science is not definitive regarding health risks from BPA, some consumers already try to limit their exposure. Among the evidence is the growth in popularity of alternatives to hard-plastic containers, including stainless steel bottles and cups for adults and children. (Top photograph courtesy of Klean Kanteen. Bottom photograph courtesy of Thermos L.L.C.) 38
How Much Evidence is Enough? Given this complex context, a clear, science-based strategy for identifying, screening and regulating suspected endocrine-disrupting compounds is badly needed. Nearly 40 years after DDT, the first recognized endocrine disruptor, was banned, new chemicals in the U.S. market are not routinely screened or tested for endocrinedisrupting properties. Congress created
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the Endocrine Disruptor Screening and Testing Advisory Committee in 1996 to recommend how the EPA should test and screen these compounds, but progress has been frustratingly slow. A list of compounds to be screened was not compiled until April of 2009, and it included only 67 chemicals, a tiny fraction of the thousands now suspected of having endocrine-disrupting properties. It also has not yet been determined how the screening should be conducted and which biological endpoints should be used. It remains unclear how much evidence is needed to evaluate health risks from compounds such as BPA. The NTP used 261 publications to conclude that there is “some concern” regarding BPA exposure. The FDA, using far fewer, has so far insisted there is little to no risk. Who is right? Most of the studies used by the NTP were conducted in university laboratories. In contrast, the FDA relied mostly on data provided by industry. This schism occurred because the NTP reviewed scores of studies by academic scientists. In contrast, the FDA relies most heavily on studies conducted using a set of guidelines called “good laboratory practices” (GLP). These guidelines specify how data must be organized and deal mostly with quality assurance, but they do not necessarily assure good study design, use of appropriate controls or robust statistical analysis. GLP studies are expensive. Thus they are nearly all conducted by private industry or contract labs, not academic labs. U.S. health agencies need to update their risk assessment strategies so that all of the data being generated and analyzed by agencies such as NIH, FDA and EPA are coordinated, shared and given equal scrutiny. Although research to date is not conclusive, there certainly is sufficient evidence to warrant concern about potential long-term effects from BPA exposure. Only a handful of studies have looked at associations between BPA exposure and disease outcomes in humans, some of which have found correlations. It is not ethically sound to expose people to a suspect compound and watch what happens. Even if it were, it would take many years for our slow-to-mature species to display any effects from the encounters. Research in animals, however, is robust. It indicates that BPA may disrupt reproductive tract development, sex-specific neuro-
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endocrine circuitry and fertility, even at doses considered relevant for humans. Since laboratory animals are used in other aspects of human health research, including drug development, it is reasonable that evidence obtained from them should play a central role in any comprehensive human-risk assessment for BPA. When combined with human epidemiological studies, cell-culture assays and high-throughput genomic studies, evidence from experimental animals is likely the best tool we have to make predictions about human risk. That is especially true for the long-term consequences of early exposures during critical developmental windows. DDT: A Lesson From History If rigorous scientific assessment doesn’t take the lead in deciding the fate of BPA, politics could, as happened with DDT regulation decades ago. That could open doors to long-term uncertainty and discord. The unintended environmental impacts of DDT were eloquently documented in Rachel Carson’s 1962 best selling book Silent Spring, which launched the modern environmental movement. Carson argued that by liberally spraying pesticides in our zealous determination to destroy “pests,” we risked the systemic destruction of our environment and ourselves. No scientific consensus on DDT’s true threat to people was reached, but in the summer of 1972 the EPA’s top administrator, William Ruckelshaus, announced a near ban of the compound anyway. Nearly 40 years later, the DDT debate is not over. Most countries banned the agricultural use of DDT by the 1990s, but it is still used in many parts of the world to control mosquitoes, especially where malaria, a disease that kills more people than cancer, heart disease or AIDS, is endemic. Whether DDT causes disease or impairs reproductive development remains the subject of investigation and a controversial topic. Many scientists and policy makers are skeptical that it does; others are convinced. Of course, DDT undoubtedly saved lives, and likely still does. No such case can be made for BPA. It is time to develop a clear and comprehensive strategy for assessing the potential public health consequences of endocrine disruptors such as BPA that may contribute only economic value. Failing to do so may put future generations at unnecessary risk. While the international debate over BPA’s safety continues, we continue to www.americanscientist.org
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be exposed, not only to BPA, but also to the many compounds like it. Bibliography Aksglaede, L., K. Sorensen, J. H. Petersen, N. E. Skakkebaek and A. Juul. 2009. Recent decline in age at breast development: the Copenhagen Puberty Study. Pediatrics 123: e932–939. Calafat, A. M., Z. Kuklenyik, J. A. Reidy, S. P. Caudill, J. Ekong and L. L. Needham. 2005. Urinary concentrations of bisphenol A and 4-nonylphenol in a human reference population. Environmental Health Perspectives 113:391–395. Durando, M., L. Kass, J. Piva, C. Sonnenschein, A. M. Soto, E. H. Luque and M. Muñozde-Toro. 2007. Prenatal bisphenol A exposure induces preneoplastic lesions in the mammary gland in Wistar rats. Environmental Health Perspectives 115:80–86. Jirtle, R. L., and M. K. Skinner. 2007. Environmental epigenomics and disease susceptibility. Nature Reviews Genetics 8:253–262. Joensen, U. N., N. Jorgensen, E. Rajpert-De Meyts and N. E. Skakkenbaek. 2008. Testicular dysgenesis syndrome and Leydig cell function. Basic and Clinical Pharmacology and Toxicology 102:155–161. Newbold, R. R., W. N. Jefferson and E. Padilla-Banks. 2009. Prenatal exposure to bisphenol A at environmentally relevant doses adversely affects the murine female reproductive tract later in life. Environmental Health Perspectives 117:879–885. Newbold, R. R. 2008. Prenatal exposure to diethylstilbestrol (DES). Fertility and Sterility 89:e55-56. Ohkura, S., Y. Uenoyama, S. Yamada, T. Homma, K. Takase, N. Inoue, K. Maeda and H.
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Tsukamura. 2009. Physiological role of metastin/kisspeptin in regulating gonadotropinreleasing hormone (GnRH) secretion in female rats. Peptide 30:49–56. Patisaul, H. B., K. L. Todd, J. A. Mickens and H. B. Adewale. 2009. Impact of neonatal exposure to the ERalpha agonist PPT, bisphenolA or phytoestrogens on hypothalamic kisspeptin fiber density in male and female rats. Neurotoxicology 30:350–357. Peterson, J. P. et al. 2009. Why public health agencies cannot depend on good laboratory practices as a criterion for selecting data: the case of bisphenol A. Environmental Health Perspectives 117:309–315. Simerly, R. B. 2002. Wired for reproduction: Organization and development of sexually dimorphic circuits in the mammalian forebrain. Annual Review of Neuroscience 25:507–536. Swan, S. H., E. P. Elkin and L. Fenster. 2000. The question of declining sperm density revisited: An analysis of 101 studies published 1934–1996. Environmental Health Perspectives 108:961–966. Vandenberg, L. N., M. V. Maffi, C. Sonnenschein, B. S. Rubin and A. M. Soto. 2009. Bisphenol-A and the great divide: a review of controversies in the field of endocrine disruption. Endocrine Reviews 30:75–95.
For relevant Web links, consult this issue of American Scientist Online: http://www.americanscientist.org/ issues/id.82/past.aspx
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Phoenix on Mars The latest successful landing craft has made new discoveries about water on the red planet
Walter Goetz
S
ince we received our first close-up photographs of Mars, when Mariner 4 flew by it in 1965, our nearest neighbor has appeared to be much like our own planet in many ways, but also distinctly different. Mars is about half the size and has about 40 percent of the gravity of Earth, it’s at least 55 million kilometers away (depending on the two planets’ positions in their orbits), and it currently takes at least nine months to get there. But like Earth, Mars has polar ice caps, clouds in its atmosphere and seasonal weather patterns. It has familiar geological features, such as volcanoes and canyons. However, although there are signs of floods in the ancient past, Mars is now apparently a barren world. What is the history of liquid water on Mars? Has water ever been stable on its surface (or in its near subsurface) for a geologically significant period of time? Was Mars warm and wet in ancient times? If so, what triggered the apparent change in climate? And could primitive terrestrial life-forms evolve in the present or past Martian environment? These are the main questions that have driven the exploration of Mars since the mid-1960s. In addition, if humans ever tried to travel to, or even set up an outpost on, another Walter Goetz received his Ph.D. from the Center for Planetary Science at the University of Copenhagen in 2002. He is a physicist at the Max Planck Institute for Solar System Research in KatlenbergLindau, Germany, and a member of the team that developed the robotic-arm camera for the Phoenix lander. He participated full time with the Phoenix primary mission operations at the University of Arizona, Tucson, in 2008, and with the Mars Exploration Rover primary mission operations at the Jet Propulsion Laboratory in 2004. He is part of the team developing instruments for the European Space Agency’s upcoming ExoMars rover. Address: Max Planck Institute for Solar System Research (MPS), Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany. Email: __________
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planet, Mars would likely be the first choice, so there’s even more reason to learn as much as possible about our neighboring planet. Missions to Mars have been a mix of failure and success. The first working spacecraft to land on the planet’s surface were Viking 1 and 2 in the mid-1970s, and they returned the first color images of the planet. They also sent back data long past their planned mission lifetime, until 1982 and 1980, respectively. Their experiments on Martian soil, looking for signs of microscopic life, were inconclusive. More than a decade later, a mission to send an orbiter to Mars ended in failure, but another, Mars Global Surveyor, arrived in 1997 and returned data until October 2006. Also in 1997, the Mars Pathfinder lander, with its Sojourner rover, landed safely and was remarkably successful. In 1999 the Mars Climate Orbiter and the Mars Polar Lander both failed and were lost upon arrival at Mars. The Mars Surveyor 2001 mission, including an orbiter, a lander and a rover, was canceled in 2000, but its orbiter was repurposed and successfully launched as the 2001 Mars Odyssey orbiter. This orbiter has also relayed information back from the twin rovers, Spirit and Opportunity, which landed in 2004. The European Space Agency (ESA) saw the safe arrival of its orbiter, Mars Express, in 2003, although the lander was lost on deployment. The Mars Reconnaissance Orbiter safely joined Mars’s orbit in 2006, providing the highest camera resolution yet. However, after the Mars Polar Lander crashed and the Mars Surveyor 2001 mission was canceled in 2000, there seemed to be no hope for a new mission to the Martian arctic regions. The situation changed early in 2002 when the Mars Odyssey orbiter discovered large amounts of near-surface hydrogen in exactly these regions. The hydrogen reservoir was in-
terpreted as water ice—less than a meter below the surface. It was argued that such arctic water ice might contain the long-searched for (and long-missed) organic compounds that could signify the presence of life, either past or present. These discoveries led a group, headed by Peter H. Smith of the University of Arizona, to develop a mission that would build on previous designs and use the already completed, but unused, Mars Surveyor lander. Thus was born the Phoenix Mars Lander, named because like the mythical bird, it had been resurrected from the ashes of its predecessors. The rocket that carried Phoenix was launched on August 4, 2007, and the spacecraft landed safely on May 25, 2008. Anatomy of a Lander Phoenix’s suite of scientific instruments includes several imaging systems that have different levels of resolution. From lowest to highest resolution, these instruments are its stereo surface imager (SSI), which can show about 1 millimeter per pixel; a robotic arm camera (RAC), with a resolution of more than 24 micrometers per pixel; an optical microscope that can reach about 4 micrometers per pixel; and an atomic force microscope (AFM) that can show about 0.1 micrometers per scan. Our group at the Max Planck Institute for Solar System Research, in collaboration with the University of Arizona, contributed the RAC and the focal-plane assembly of the optical microscope. The lander also has a wet chemistry laboratory unit (WCL), where it can mix Martian soil in liquid water. The unit consists of four such cells, each designed for a single use. The resulting aqueous solution is analyzed by ion-selective electrodes, which provide information on the compounds in the soil (such as salts) that are soluble in liquid water. Another important instrument is a thermal analyzer, designed to heat soil
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Figure 1. More than a simple tourist snapshot of itself in an exotic locale, this self-portrait of the Phoenix lander shows a remarkable feat: the safe arrival, descent and landing of the spacecraft onto the surface of Mars, a result that is still not a given for interplanetary missions. Not only that, the lander also carried out a series of studies on water ice, soil chemistry and weather patterns over the course of several months in 2008. Phoenix is a Cinderella story, as the lander was originally constructed for the cancelled 2001 Mars Surveyor mission. Its resurrection and deployment to Mars’ polar regions has provided great insights into the water cycle on our neighboring planet. This panorama of the lander, showing its robot arm partially deployed, was taken during the first few days after landing. (Image courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University.)
samples up to 1,000 degrees Celsius; the evaporating gases are then studied by mass spectroscopy. This instrument group (referred to as the Thermal and Evolved Gas Analyzer, or TEGA) should be able to characterize the inventory of potential organic compounds in the Martian soil by detecting either the parent organic molecules or their thermally generated fragments, as the temperatures where specific gases are released constrain the identity of the parent compound. As the amount of heat is increased at known levels, any additional increase in temperature also reveals phase transitions in the comwww.americanscientist.org
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pounds, which can possibly be identified by their enthalpic characteristics. The spacecraft also has a robotic arm that is in itself a scientific instrument, as it allows the lander to characterize the physical properties of the soil. The scoop at the end of the 2.3-meter-long arm allows controllers to select and transfer specific soil samples to various instruments. An ice drill is mounted to the backside of the scoop. The robotic arm camera is positioned on the arm so that it can see into the scoop and image the collected soil sample at high resolution. A sensor mounted next to the scoop can measure the soil’s electric and thermal
conductivity between four needles. An additional sensor can measure the atmospheric water vapor pressure and the relative humidity of the atmosphere. A meteorological mast, provided by the Canadian Space Agency, collects data about the Martian weather that help describe how water cycles between the solid and gas phases at the landing site. Its central instrument is a LIDAR (Light Detection And Ranging) that probes the vertical structure of the atmosphere by measuring the travel time of its emitted light as it is backscattered by suspended particles (such as dust and ice) in the air. Pressure and temperature sensors are 2010 January–February
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meteorological mast with weathercock
western solar panel UHF antenna
chute for transfer of soil material to the OM
four WCL cells
evolved gas analyzer
thermal analyzer organic-free blank first segment of the robotic arm
LIDAR
stowed biobarrier Figure 2. An image of the lander by its stereo surface imager shows a number of Phoenix’s scientific instruments. At left, a LIDAR (Laser Detection And Ranging) is used in conjunction with the metorological mast and weathercock for weather studies. A UHF (ultra-high frequency) antenna relays data to an orbiting satellite. The lander has two large circular solar panels, the western-facing one of which is shown. A chute is used to transfer soil samples to the optical microscope (OM). A wet chemistry laboratory (WCL) has four cells in which it can mix soil samples with liquid for analysis. A thermal analyzer and evolved gas analyzer heat samples and look at the gases emitted, respectively. A Teflon block, called an organic-free blank, is used to serve as a baseline reference for organic molecules. One segment of the robotic arm can be seen at the right of the image, next to a trench about 20 centimeters wide (white circle) that was later analyzed for water ice. The inset at upper right shows a foldable cover, called a biobarrier, that protected the robotic arm and scoop from biological contamination during flight. This cover folded towards the front of the lander and was stowed after landing. (Image courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University; inset image courtesy of IEEE and R. G. Bonitz, NASA/JPL.)
mounted to the mast at three different heights above the deck (25, 50 and 100 centimeters), and the mast is topped by a Danish-produced weathercock (telltale, or wind indicator). The SSI provides complementary data on the atmospheric dust opacity and water vapor abundance by imaging the solar disk through specific visible and near-infrared filters. Where It All Happens Spectroscopic data and high-resolution images from various orbiters (including Mars Global Surveyor, Odyssey, Mars Express and Mars Reconnaissance Orbiter) were available prior to landing and were used extensively to select the best landing site for Phoenix, both in terms of safety and for the best chance of doing useful research. The distance from the landing site to the northern border of the volcanic Tharsis region is about 500 kilometers and to the nearest volcano (Alba Patera) is about 1,800 kilometers. The north-polar ice cap and the circumpolar dunes are located about 2,000 kilometers north of the lander. On a large scale, we expected volcanic ashes from the Tharsis province as well as sand grains from the north-polar dunes at the site. The landing site is also situated about 20 ki42
lometers west from the Heimdall crater, which has a diameter of 11 kilometers and a depth of about 1 kilometer. Thus ejected soil from these depths may also be found at the landing site. A few days after landing, the terrain below the spacecraft was examined by the RAC in order to confirm the stability of the spacecraft’s position. The first image showed a bright, even surface (called “Holy Cow”; the nomenclature followed fairy-tale themes) that was uncovered by the action of the descent thrusters. Apparently, the subsurface ice discovered by Odyssey in 2002 was right there—only a few centimeters below the surface. The images suggest that this is ice-rich regolith rather than pure water ice. Over the course of about 50 Martian days (or sols), another icy soil patch, dubbed “Snow Queen” and located just next to Holy Cow, developed numerous cracks after it lost its thermally insulating blanket of soil. During the Phoenix mission, 12 trenches were excavated, the deepest being 18.3 centimeters. The appearance of the subsurface soil was different from trench to trench. In some trenches (such as one dubbed “Dodo Goldilock”) almost pure ice was found, as determined by the spectra acquired by the SSI. Other trench-
es yielded ice-rich regolith, whereas in some no ice was found at all. In the Dodo Goldilock trench, bright centimeter-sized clumps disappeared over the course of four sols. This observation suggests that the bright material in the shallow subsurface is indeed water ice. So far, it is not clear why the ice/regolith mixing ratio varies so much within a few meters. The surface of the Martian polar environment takes on a hummocky appearance that might account for some of the soil inconsistencies. The basic model for the formation of these “polygons” was developed by Ronald Sletten and his colleagues at the University of Washington. Seasonal contraction and expansion of soil generates wedge-shaped fractures. During winter, fine-grained debris moves into these wedges and prevents them from completely closing again during the next summer. The seasonal stress generated by these processes is relaxed by the formation of mounds (or polygons) at a certain spatial frequency. The net result is a slow cyclic transport of soil material. This erosional process is known as cryoturbation and occurs frequently in terrestrial environments around the edges of glacial regions. The Heimdall crater formed about 500 million years ago. It seems likely that
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density and distance to the nearest crater may provide further understanding of the size distribution of rocks at the site. RASP
RAC TECP
Figure 3. Images from Phoenix’s stereo surface imager show the end of the lander’s robotic arm as it digs a sample of Martian soil (left). As the arm lifts up (right), its instruments can be seen: an ice drill (called the Rapid Active Sampling Package or RASP) mounted on the back of the scoop, the robotic arm camera (RAC) positioned so it can see into the scoop and image soil samples and a soil sensor (called the Thermal and Electrical Conductivity Probe, or TECP) mounted next to the scoop. (Images courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University.)
excavation of this crater contributed soil material to the landing site. Cryoturbation processes, however, take place over a much shorter time scale, continuously renewing the landscape and making the Phoenix landing site the youngest among all other past Martian landing sites (those of Viking, Mars Pathfinder or the Mars Exploration Rovers). Larger rocks or boulders (bigger than 20 centimeters or so) are absent at the
landing site. Water ice is abundant near the surface, in agreement with Odyssey 2002 data. Perhaps the absence of larger rocks can be explained by the high concentration of condensed volatiles (such as water ice) in the subsurface that were affected by the Heimdall impact: A violent explosion would have removed and crushed the rocks that may have been at the landing site initially. A future, systematic study of the correlation between rock
The Soil Itself Microscopic color images from Phoenix demonstrate the great diversity of particles in Martian soil. AFM scans have given three-dimensional representations of dust particles, but it is unclear how typical these particles may be of Martian dust in general. Reddish-orange dust dominates by volume. The individual dust particles cannot be resolved by the microscope and must therefore be on the order of 10 micrometers or less in size. According to a preliminary classification, two different types of grains are present in the soil: Reddish-brownish to colorless grains and dark (almost black) grains. The origin of these grains is uncertain, but a careful comparison to terrestrial analog soils may constrain the potential scenarios for the formation of these grains. Key Phoenix instruments, such as TEGA and WCL, have provided new insights into the microscopic structure, as well as the mineralogy, of the soil. One cubic centimeter of material transferred to one of the WCL cells was mixed with 25 cubic centimeters of aqueous solution and produced a weak alkaline solution (with a pH of about 8.3) that contained
Figure 4. The icy area dubbed “Holy Cow” was swept clean by the lander’s descent thrusters. It was imaged by the robotic arm camera, the only onboard instrument able to see beneath the lander; the light rectangle in all four images is the arm’s soil sensor. In sunlight, Holy Cow appears bright and reflective (top left), but during the reddish light of twilight, the patch is about as bright as the surrounding soil, indicating that it is not pure ice (bottom left). A neighboring region, “Snow Queen,” was also uncovered by the lander’s thrusters. The region was initially smooth (top right) but showed surface fractures after about 50 Martian days (bottom right, in white circles), indicating the sublimation of water ice. (Images courtesy of NASA/JPL/Univeristy of Arizona, and H. U. Keller and W. J. Markiewicz, Max Planck Institute for Solar System Research, Katlenburg-Lindau.) www.americanscientist.org
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Figure 5. From global to local scale, successively enlarged images zoom in on the Phoenix lander on the Martian surface. The landing site is near the northern polar ice cap of Mars (far left). A black-and-white image about 280 meters wide from Mars Global Surveyor shows that the landing site is off to the left of the circular Heimdall crater (second from left). A higher resolution orbital image, taken 22 hours after landing by the HiRISE camera aboard the Mars Reconnaissance Orbiter, barely shows the lander; the black dot at the middle right of the image is the ejected heat shield, and the bright dot near the bottom center is the parachute (middle). An enlargement of the middle image (top right) shows surface roughness and coarsergrained, darker material that was exposed by the descent thrusters. A final enlargement (bottom right) shows the lander deck and two solar panels, at a resolution of about 33 centimeters per pixel. (Images courtesy of NASA/JPL, Malin Space Science Systems and the University of Arizona.)
surprisingly large quantities of perchlorate (ClO4–), salts that could lower the freezing point of water and that have the potential to be found in a liquid-water solution under the temperature and pressure conditions on present-day Mars. This ion was by far the dominant anion (or negative ion) in the solution. Among
the cations (positive ions) were, in order of decreasing concentration, magnesium, sodium, calcium and potassium. To extrapolate from these results, one gram of Martian soil might have a perchlorate abundance of about 1 percent by weight. Such a concentration exceeds that found in some terrestrial desert
soils by orders of magnitude. Finding chlorine at the highest possible degree of oxidation has significant implications for our understanding of the chemical processes taking place on the Martian surface, as well as in the atmosphere, and raises several important questions: Is the perchlorate just an exotic compound at the Phoenix landing site, or is it widespread on the surface of the planet? Is the chlorine identified by all previous Mars lander missions mostly present as perchlorate? Even the old question of life on Mars must be reformulated: Which types of primitive (terrestrial) life-forms could have evolved in the Martian soil, given the measured perchlorate concentration? The ion-selective electrode in the WCL unit that is sensitive to perchlorate, and much less so to nitrate, provided such a strong signal that the identification of perchlorate was unambiguous (the mass of nitrate needed to explain the signal would have exceeded the total mass of the analyzed soil sample). Overall, the suite of electrodes used in Figure 6. The trench dubbed “Dodo Goldilock” is about 20 centimeters wide. The upper part of the trench reveals nearly pure ice (left). Small clusters of ice particles, about 2 centimeters in diameter, at the lower left of the trench (white circles) were visible when the trench was first dug (see enlargement at top right), but by four Martian days later, these spots disappeared (bottom right) indicating the particles had sublimated. (Images courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University.)
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Figure 7. The Martian surface near the polar ice cap often consists of uneven mounds (right), created by a process called cryoturbation. Wedge-shaped gaps form in the soil during the winter (above) and partially fill with fine-grained debris that prevents the gaps from fully closing during the summer. The resulting surface stress causes the motion of soil inwards and upwards (white arrows) creating these “polygon” surface mounds. Below the level of the permafrost and the depth of the sand wedges, the soil is not perturbed. The blue circular arrows illustrate the long-term transport of soil. (Image courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University.)
the WCL provided rich information on the water-soluble components of the soil, but each one is sensitive to a range of different ions at strongly different rates. The conversion of the electrode data into concentrations is therefore non-unique, and constraints from other instruments are needed. Thermal decomposition products of perchlorates were generally not detected by the thermal analyzer or the evaporated gas analyzer’s mass spectra, although this does not jeopardize the WCL identification of perchlorate. In at least one of the samples analyzed by these instruments (from a site called “Baby Bear”), some oxygen release in molecular form was observed that may be due to the decomposition of perchlorate. Another important finding from the mass-spectroscopy studies was the release of carbon dioxide at temperatures of 800 to 900 degrees, which indicates the presence of 3 to 5 percent by weight of calcium carbonate in the soil. The result is remarkable, given that we have been on the hunt for this mineral for many years, and Phoenix found it in the soil! Carbonates are generally the products of aqueous processes, and thus their presence may be indicative of liquid water on the surface of Mars at some point in the planet’s history. The inferred presence of carbonates is also compatible with WCL results and explains the alkaline pH of the aqueous solutions. www.americanscientist.org
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Furthermore, the absence of certain gases after heating can provide critical information on the mineralogy of the Martian soil: No sulfur dioxide has been released over the entire temperature range (from below 0 degrees, up to 1,000 degrees). This is surprising as all previous lander missions have identified substantial quantities of sulfur in the Martian soil (5 to 10 percent by weight of sulfur trioxide). The presence of sulfate ions is compatible with WCL data. Magnesium sulfate would release sulfur dioxide at temperatures below 1,000 degrees, so the absence of this gas therefore proves the absence of magnesium sulfate in the soil. In the Martian environment (with an atmospheric pressure of roughly 10 millibars, or about a hundredth of that on Earth), calcium sulfate would decompose at about 1,400 degrees, but such temperatures are not reached by Phoenix’s thermal analzyer. All these facts taken together point toward the likely presence of calcium carbonate in the soils that Phoenix has analyzed. In fact, large deposits of calcium carbonate previously have been found on the surface of Mars, in particular near the north-polar ice cap. Nice Weather Phoenix’s instruments have enabled new types of meteorological measurements at the landing site. The site has the advantage that the polar regions exhibit strong weather phenomena,
especially cloud formation (as was known from orbital imagery). Also, the weathercock has returned data on wind velocity and direction throughout the mission, enabling fruitful modeling. Phoenix weather measurements were coordinated with orbital observations on a regular basis throughout the mission, strengthening the results. Mars’s atmospheric water vapor pressure, as measured by Phoenix’s humidity sensor, rises between about 2 am and 10 am, then reaches a plateau (about 1.8 Pascals) that is maintained throughout most of the day. In contrast, atmospheric temperatures continue to rise until about 2 pm. Apparently atmospheric convection becomes very efficient and rapidly redistributes the newly formed water vapor after 10 am. The spacecraft observed several passing dust devils at typical wind velocities (5 to 10 meters per second). Analysis of the pressure data acquired throughout the mission shows that such dust devils are correlated with brief pressure dips of 1 to 3 Pascals. LIDAR data from the later part of the mission turned out to be particularly important: Ground fog as well as water-ice clouds near the top of the atmospheric boundary layer (at an altitude of about 4 kilometers) formed every night after sol 80. Many of these clouds had “fall streaks” formed by initially growing, free-falling, then eventually sublimating ice crystals. Such fall streaks also can be 2010 January–February
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Figure 8. Images of Martian soil from Phoenix’s optical microscope show a mix of lighter and darker colored grains, about 60 micrometers in diameter (left), distributed through a matrix of reddish-orange dust, about 10 micrometers in diameter (right). A detail of a dust particle from the atomic force microscope (upper left) corresponds to an area about the size of the small rectangle. (Images courtesy of NASA/JPL/University of Arizona, M. H. Hecht, JPL, and W. T. Pike, Imperial College, London; inset courtesy of NASA/JPL and U. Staufer, Technical University Delft, The Netherlands.)
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observed in terrestrial clouds. Daytime LIDAR data showed mostly dust in the atmospheric boundary layer. However, SSI also documented many daytime clouds late in the mission. In some cases these clouds disappeared by sublimation over a timescale of 10 minutes. Phoenix’s instruments monitored the complete diurnal water cycle: During morning hours water vapor is released into the atmosphere. The sources for the water vapor include the shallow subsurface water ice, water adsorbed to soil grains and, possibly, crystal water in perchlorates. During the night, water vapor condenses and falls out by gravity. Most of these ice crystals sublimate again on their descent through the atmospheric boundary layer. In some cases snowfall was observed, when the fall streaks extended all the way down to the surface. Where Phoenix Is Now Phoenix surface operations lasted from Martian late spring to late summer— May 26 to November 2, 2008, or 152 sols. The polar night at the landing site lasted from April 1 to July 10, 2009. Since that time, the Sun has again risen above the horizon at the landing site. If the spacecraft—contrary to all expectations—survived both the low temperatures (150 kelvins) of the Martian winter and the dry-ice load built up on its solar panels, it will be able to reanimate itself through a so-called “Lazarus mode.” Mars Odyssey was scheduled to search for Phoenix signals starting at the end of 2009. Independent of its potential reanimation, Phoenix was a highly successful mission that provided on-site geochemical and atmospheric data for the first Martian arctic landing site ever explored. No organic molecules, and no traces of previous or present biological activity, were found at the landing site. Hence, the search for organic molecules will have to be continued by future missions. It should be noted that organic molecules ought to be present in the Martian soil because of the steady influx of certain types of meteorites that contain Figure 9. On day 104 of Phoenix’s mission, the lander spotted a dust devil about a kilometer away (top left). The dust devil movedto the right and away from the lander (two middle images, at left), ending up about 1.7 kilometers away (bottom left). The presence of the dust devils correlates with brief dips in the atmospheric pressure. Larger dust devils have been observed previously in Mars’s Gusev crater. (Images courtesy of NASA/JPL/University of Arizona and M. T. Lemmon, Texas A&M University.)
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Figure 10. Phoenix’s LIDAR was able to characterize the clouds and ground fog that form at night on Mars, as shown by the intensity of light backscattered from ice and other particles (above left). Ice clouds at the atmospheric boundary layer, about four kilometers in altitude, often show fall streaks from the sublimation of freely falling ice crystals (above right). The size of the ice particles can be calculated from their descent velocities. Similar cloud formations can also be seen on Earth (right). (Graphs courtesy of NASA/JPL/ University of Arizona and J. A. Whiteway, York University, Canada; photograph courtesy of Marc Thiessenhusen.)
substantial quantities of organic material. The fact that no such molecules have been found in the soil around Phoenix is indicative of fast geological degradation processes. The ever-continuing turnover of soil material (by cryoturbation) at the landing site may have favored such degradation processes. If organic molecules are ever detected it will be a major scientific task to track down their origin: Are they imported by comets or meteorites, or do they truly attest to primitive, extinct life-forms on the surface of Mars? Although no organics have been found so far, it is essential to continue this exploration program and search for organic material in more protected environments, such as the interior of sedimentary rocks or deeper soil layers. The next scheduled missions that are available for this task are the rovers Curiosity (which NASA plans to launch in 2011) and ExoMars (which ESA plans to launch in 2018). They will carry complex follow-up instruments that will search for organic molecules in specific equatorial regions. One instrument for ExoMars, the Mars Organic Molecule Analyzer, is presently under development at the Max Planck Institute for Solar System Research. Curiosity’s Sample Analysis at Mars (SAM) instrument has been built by the www.americanscientist.org
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NASA Goddard Space Flight Center and is ready to go. It will be able to detect particularly low concentrations of potentially organic material. Special attention will be given to the molecule methane (CH4) whose presence on Mars recently has been demonstrated. The instrument will be able to measure at extremely low methane concentrations (less than one part per billion) the ratio of the isotopes of carbon-13 and carbon-12 present in a molecule. Such data may shed light on the molecule’s origin, favoring either geochemical or biological formation. There is little doubt that Mars will continue to present fascinating new data, surprises and mysteries for these upcoming missions, and to ones still on the drawing board. The two new rovers, Curiosity and ExoMars, will be important benchmarks on that path. Further in the future, robotic return of samples will play a major role in the Mars exploration program. The biggest challenge—a manned mission to Mars—may belong to the distant future, but perhaps at some point such projects will be within reasonable budgets for the major space agencies.
Bibliography Boynton, W. V., et al. 2009. Evidence for calcium carbonate at the Mars Phoenix landing site. Science 325(5936):61–64. Hecht, M. H., et al. 2009. Detection of perchlorate and the soluble chemistry of Martian soil at the Phoenix lander site. Science 325(5936):64–67. Langevin, Y., F. Poulet, J.-P. Bibring, B. Schmitt, S. Douté and B. Gondet. 2005. Summer evolution of the north polar cap of Mars as observed by OMEGA/Mars Express. Science 307:1581–1584. Sletten, R. S., B. Hallet and R. C. Fletcher. 2003. Resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground. Journal of Geophysical Research 108(E4):8044. Smith, P. H., et al. 2009. H2O at the Phoenix landing site. Science 325(5936):58–61. Whiteway, J. A., et al. 2009. Mars water-ice clouds and precipitation. Science 325(5936):68–70.
For relevant Web links, consult this issue of American Scientist Online: http://www.americanscientist.org/ issues/id.82/past.aspx
2010 January–February
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Neural Interfaces Communicating with the nervous system through implanted devices requires engineering solutions to biomedical problems
Warren M. Grill
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neural interface is an engineered device designed to exchange information with the nervous system. Signals can be introduced by localized electrical stimulation of neurons, and information can be captured by recording the electrical activity of neurons over time. Injuries to peripheral nerves or the spinal cord often result in catastrophic loss of function—limbs and organs become disconnected by the equivalent of cut wires. A possibility that energizes researchers in the field is that the connections and physiological functions can be restored by the development of devices that supply a bridge for the interrupted signal. A computer listens to a keyboard and communicates to a printer through cables. At the ends of the cables are specific adapters. Neural interfaces are adapters that can collect neural signals, port them through feedback and control circuits, and deliver them to neural circuits downstream from the cause of disruption in neural traffic. Neural routes that had fallen silent after injury can again become conductors of physiological signals, with potentially life-changing restoration of function.
Warren Grill is a professor of biomedical engineering at Duke University’s Pratt School of Engineering. His research interests are in neural engineering and neural prostheses, and include design and testing of electrodes and stimulation techniques, the electrical properties of tissues and cells, and computational neuroscience with applications in restoration of bladder function, treatment of movement disorders with deep brain stimulation and multi-joint limb movement. Address: Duke University Department of Biomedical Engineering, Hudson Hall, Room 136, Box 90281, Durham, NC 27708-0281. Email: _____________
[email protected] 48
Basic neural interfaces already have important medical roles, but there is far greater potential on the horizon if an array of fundamental biophysical and biomedical challenges can be overcome. The challenges fall into the following categories: selectivity —small numbers of neurons must be monitored and addressed uniquely in a noise-ridden environment; stability—optimally, surgically implanted interfaces will interact with specific neurons over a time frame of years; resolution versus invasiveness—a balance must be achieved between the selectivity of the signal and the degree to which delicate physiological structures will tolerate the intrusion of the device; and management of host-interface responses—reducing tissue reactions such as inflammation and scarring, which plague implanted devices today, will be critical in achieving selectivity, stability and resolution in long-term implants. Approaches to overcoming these challenges include empirically derived advances in electrode design, building on ongoing experiments in material selection and geometry; biochemical manipulation of the injury response and healing; and in the case of electrical activation of the nervous system, experimental analysis of the response to changes in the timing, amplitude, and polarity of stimulation waveforms. On the horizon, research is being done on single-cell electronic connections— silicon-neuron hybrid circuits—and alternatives to stimulation by electrical current, including genetic modifications that produce neurons that can be activated by light.
The Wiring of the Body Electric Communication through the nervous system takes the form of action potentials, which consist of rapid, transient changes in the polarization state of nerve cells (see Figure 2). The number, rate and pattern of action potentials can be recorded to acquire information from the nervous
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Dr. Richard Kessel and Dr. Randy Kardon/Tissues and Organs/Visuals Unlimited/Corbis
Figure 1. This cross section of a sciatic nerve shows the tight bundling of nerve fibers. The whitish rims are sheaths of myelin that wrap around myelinated nerves. Severing of a nerve bundle results in loss of physiological communication in two directions. Motor instructions in one direction and sensory and feedback information in the other vanish into the gap between the cut nerve ends. Neural interfaces are bioengineered devices designed to introduce information into the nervous system and eavesdrop on messages passing through the nerve channel. “Plugging in” to the nervous system is a commonplace of science fiction; in reality, interfacing with neural structures presents daunting medical and engineering challenges. In this article, Warren M. Grill reviews the problems and solutions that have emerged in the pursuit of stable, specific, high-fidelity, high-density communication between neurons and external devices. At stake are potentially life-changing therapies for individuals who have lost physiological function through neurological injury or disease, including potential restoration of lost motor function, recovery of feedback control over organ function and many other applications. www.americanscientist.org
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time (milliseconds) Figure 2. Neural messages are communicated through action potentials, which are transient waves of depolarization that travel down the axons of neurons, the excitable cells of the central and peripheral nervous system. At rest, neurons are polarized with a transmembrane voltage of about –60 millivolts (negative inside). In reponse to signals from other neurons, the membrane voltage can rise until it crosses a threshold potential, at which point voltage-dependent transmembrane channels open and allow the passage of positively charged sodium ions into the cell, rapidly depolarizing a local region of the axon (top graph). Sodium influx is followed by the opening of voltage-dependent potassium channels in the same membrane that allow positively charged potassium ions to flow down their concentration gradient out of the cell. At the peak of the action potential, the influx of sodium ceases, and the somewhat longer efflux of potassium decreases the transmembrane potential toward its resting potential. In the bottom graph this counterflows of sodium and potassium is shown as conductance curves through their respective transmembrane ion channels. Depolarization in a local region of the axon spreads to the adjacent region down the axon, causing the threshold potential there to be reached and initiating the same channel events, which thus propagate down the length of the axon. In myelinated cells such as the one shown (above right), ionic fluxes occur in gaps between the myelin sheaths called nodes of Ranvier. The potential changes assocated with action potentials at the gaps are communicated at very high speed between the nodes; thus, myelination greatly accelerates the speed of action-potential propagation.
system, and action potentials can be induced by tiny currents that cause the depolarization of nearby nerve cells and nerve bundles. Depolarization beyond a threshold amount is the trigger for an action potential. The peripheral nervous system (PNS) relays information to and from the central nervous system (CNS), comprising the brain and spinal cord. Motor instructions and sensory feedback are conducted in opposite directions through nerve cell axons that lie side by side in the same nerve bundles. The nerves of the PNS consist of both bare fibers and fibers wrapped 50
in myelin. The myelin sheath insulates the nerve fibers, and it contributes to speedier transmission of action potentials by acting as a spacer between clusters of ion channels on the axon surface that open in response to voltage changes across the membrane. The depolarization that occurs during an action potential arises when positive ions flow into the nerve fiber, which is polarized (negative inside) in its resting state. Propagation of the action potential occurs as depolarization in a region of the nerve fiber spreads to cause voltage-gated ion chan-
nels in adjacent regions to open. The depolarization is communicated at much higher speed along segments sheathed in myelin, leaping between the gaps between myelinated segments. In discussing interfacing with the PNS, we are mainly interested in myelinated nerve fibers, which carry messages rapidly over long distances. Nerve fibers are organized in bundles called fascicles, which are themselves bound in nerve cables that branch from peripheral nerve trunks. Helpfully, the topological arrangement of nerve bundles is
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related to the eventual anatomical targets of the neural signals. Classic anatomical studies by Sir Sydney Sunderland in the 1960s and 70s, confirmed and expanded by recent work, have shown that in the more peripheral parts of a nerve trunk, motor axons are grouped in fascicles that innervate single muscles or small groups of synergistic muscles. Careful staining experiments have shown that nerves innervating the fingertips of monkeys form a discrete geometrical group through the carpal tunnel of the wrist and all the way through the upper arm. If this were not the case, it would be much more difficult to discover where to introduce targeted signals intended to initiate specific motor responses. Geometry also assists because nerves that will branch at upcoming junctures are at the surface of nerve bundles—nerves peel off the central trunk from the outside layers. Nevertheless, there are difficult problems posed by the geometry of the nervous system. Nerve cables are three-dimensional bundles, with most axons buried within the bundle. And here we run into a fundamental challenge of neural interfacing. To deliver or record signals effectively and selectively, an electrode must be implanted very close to the targeted nerve fiber, while avoiding injury arising from the implantation. Links with Cuff Electrodes The challenge of selectivity turns on two fundamental properties of nerve fiber stimulation: The current required to stimulate a neuron with an extracellular electrode depends on the distance between the electrode and the nerve fiber—the current-distance problem; it also depends on the diameter of the nerve fiber—the current-diameter problem. Due to biophysical characteristics of nerve fiber polarization, nerve fibers of larger diameter require less stimulating current. Nerves are delicate anatomical structures. Simply piercing nervous tissue with an electrode is a direct and effective technique suitable for laboratory experiments on cultured cells, but the accompanying trauma is undesirable for therapeutic interfacing with the structures of the peripheral nervous system. A contemwww.americanscientist.org
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Figure 3. Cuff electrodes affix a set of individually addressable electrical contacts to the surface of a nerve bundle, allowing selective stimulation and recording without violating the integrity of the nerve. The Flat Interface Nerve Electrode (FINE, above right) interfaces with a flattened nerve, which places interior nerve fibers closer to the electrical contacts of the cuff.
porary solution is cuff electrodes, which generally include several independently addressable conductive electrodes embedded in an insulating sheath (cuff). The cuff is surgically positioned with the electrodes directly contacting the surface of peripheral nerve trunks. The cuff exploits the current-distance relationship to enable selective and graded stimulation of an individual nerve fascicle lying closest to the electrode contact, ideally with minimal stimulation of fascicles more distant from the contact point. One of the advantages of an encircling cuff of multiple, independently addressable electrodes is that the cuff can be installed without precise foreknowledge of the specific nerves being contacted. Once in place, a feedback device can then learn which electrodes to address by monitoring for functional outcomes in response to stimulation. In an early experimental use of the nerve cuff electrode, a multi-electrode cuff was placed around the optic nerve of an individual who had total loss of vision due to photoreceptor loss. Stimulation through the individual electrodes in the cuff generated visual sensations (phosphenes), notably in different portions of visual space, which is reflective of how the retina, optic nerve and visual cortex are organized. Early animal studies revealed the challenges of such interfaces, including variability in the effectiveness of stimulation and record-
ing. The classic response to foreign materials in tissue is a covering of fibrotic connective tissue. It had been hoped that tissue encapsulation accompanying healing would stabilize the cuff and the electrodeneuron interface, but in some instances, variability in input-output properties remained. Furthermore, there was evidence of mechanically induced neural injury, although the injury seemed to have minimal effect on the electrophysiological performance of the installation. The connection between performance and longer-term acquisition of injury-related damage remained uncertain as research moved to studies of humans wth neurological diseases or injuries. In recent work, cuffs have been installed in humans to attempt the restoration of upper-extremity motor function. Initial studies were conducted during unrelated surgical procedures during which nerves were exposed. Measurements were made on stimulation thresholds and selectivities that extended what had been learned from pre-clinical animal studies. Running through the choice of electrode contacts, researchers were able to activate certain target muscles from about 30 percent to nearly 100 percent activation before the activation spread to other muscles. This encouraging result was followed by the implantation of four nerve-cuff electrodes in an individual with tetraplegia (paralysis of all four limbs). The perma2010 January–February
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nently implanted electrodes exhibited long-term stable thresholds while selective stimulation conferred functional movements such as lifting of the arm (shoulder abduction), elbow flexion and extension, and extension of the wrist and fingers. While the level of control achieved was coarse, it was a significant leap beyond no control at all and opened vistas on what will be medically possible. In some therapeutic interventions, a nonspecific aggregate signal readily achieved by an electrode cuff is valuable in restoring function. Foot drop is a malady in which neurological damage renders an individual unable to turn the ankle and toes upwards, resulting in an awkward foot-slapping gait. A nerve cuff collecting an aggregate signal has been used to detect heel strike on the ground, triggering electrical stimulation of muscles that compensates for foot drop. Similar signal detection can be used to recognize the onset of an object slipping from the fingers of an individual with compromised grasp, triggering a stimulating signal to restore grip. In these applications, the recorded signal is an aggregate of many nerve fibers within a cuff. The selectivity of the recording is coarse but sufficient to drive a feedback circuit that delivers a marked functional improvement. A FINEr Cuff Advances in cuff design attempt to counter the challenging threedimensional geometry of the fascicle by changing the geometry. The Flat Interface Nerve Electrode (FINE) flattens the round cross-section of nerve bundles, which increases the perimeter of the nerve, bringing more nerve bundles into reach, and bringing nerves in the center of the nerve bundle closer to the encircling electrodes. Flat interface electrodes have proven to be well tolerated, and they can be selective enough to enable stimulation even of subregions of individual fascicles. For both flat and round electrode cuffs, the direct contact between cuff and nerve can result in nerve damage, and pressure from the cuff may cause demyelination, which impedes neural conduction. Recent work suggests that these problems may be avoidable by implanting 52
cuffs at regions of minimal nerve flexion, such as toward the center of long bones. Cuff electrodes can also be customized, with a variety of sizes available for cuffs that are destined for specific nerves. A range of softer and more readily tolerated materials is being explored
Figure 4. The regenerative sieve electrode is engineered to exploit the growth capability of nerve endings, leading to intimate connections between the nerves and the electrical contacts that line the perforations of the sieve assembly.
for the insulating cuff, and progress is being made on determining the snugness of fit that gives the best tradeoff of fidelity versus tissue damage and fibrosis. Intraneural Electrodes A very high degree of selectivity can be achieved by threading electrodes inside the length of an axon bundle. Electrodes of very fine platinumiridium wire implanted in the sciatic nerve of the cat have been shown to stimulate so selectively that only portions of targeted fascicles were activated by the stimulating current, resulting in activation of single muscles—very high fidelity indeed. An additional advantage is very low stimulation thresholds—an order of magnitude lower than those required for the extracellular stimulation provided by cuff electrodes. A drawback of intrafascicular electrodes is the invasiveness of the implant. Insertion of the electrode necessarily violates the protective tissue around the nerve bundle, breaching the blood-nerve barrier and disrupting the chemical and mechanical microenvironment on which continued nerve function de-
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pends. Edema, fibrosis and loss of nerve fibers are common results. As with other interface techniques, advances are being made in techniques for installing the devices and managing the healing response. Regenerative Electrodes A particularly selective and stable nerve-electrode contact can be made if individual nerves are coaxed to grow into contact with engineered receptacle electrodes. Axon-guidance techniques use structural cues to guide the nerve, such as aligned poly PAN-MA (acrylonitrile-methacrylate) nanofibers that form conduits for growth. Paths for growth may also be constructed by creating tracks of growth factors, proteins of the extracellular matrix and other biological molecules that influence the growth of the fiber as part of their biological function. In the regenerative sieve electrode, a perforated disk is apposed to the end of a severed nerve, allowing cell processes—wiry extensions of the cell—to grow through the holes in the disk. The lining on the inside wall of each perforation serves as an individually addressable electrode, and the sieve electrode is seized to the end of the nerve by the processes that grow through the perforations, providing a measure of stability. However, the resulting fibers tend to be small— small fibers require higher stimulating currents—and they may have diminished or absent myelin sheaths. Current work suggests that sieve electrode holes larger than 40 micrometers may contribute to adequate nerve-end regeneration. As regenerative techniques develop, the stability of implants will likely be enhanced, and the signal-tonoise ratio will be improved by maximizing the proximity of the electrode to a specific nerve. Signal to Noise The small amplitude of neural signals and the ratio of signal to noise pose significant challenges for neural interfacing. The average resting potential of mammalian neurons is approximately –60 millivolts, which can reach positive values during the passage of an action potential. Electrodes that penetrate the neuron may encounter this level of signal, but the signals recorded from extracellular electrodes are much lower. For example, in regenerative electrodes, in which the nerve pro-
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cesses that grow toward an electrode may be very fine, the signal that is encountered may be just a few hundred microvolts—amidst a cloud of noise. When attempting to use captured signals to direct motor functions, the difficulty is compounded by a basic physiological fact: Muscle is noisy. Neural signals near contracting muscles can be swamped by the much larger-amplitude electrical signals created by muscle activation (the electromyogram or EMG). In addition, if recording and stimulation are being done simultaneously, the electrical stimulation signal may swamp the recording with large electrical artifacts. These problems are addressed in part by the properties of cuff electrodes. All action currents are corraled within the volume of the cuff, and the recording electrodes are to some degree shielded from muscle electromyograms or stimulation artifacts by the insulating properties of the cuff. A more comprehensive solution is to move the neural interface upstream along the axon to the cell body of the neuron in the dorsal root ganglion of the spinal cord. (Neuron cell bodies reside in the dorsal root and project axons to the periphery, in some cases as much as a meter away.) Silicon-based implants in the dorsal ganglion offer the promise of stability, and the combination of simultaneous recordings from just 8 to 10 single axonal units can yield acceptably high-fidelity interpretations of limb position and motion, supplying the foundation for a therapeutically useful feedback and control circuit. Connections in High Places Interfacing to the central nervous system itself—the brain and spinal cord—is now a major focus of neuroengineering. Examples of therapies under intense study include the use of deep brain stimulation to regulate mood disorders, epilepsy, and Parkinson’s symptoms. Much work is also being done on developing the ability to control devices with a brain-computer interface. Overall, the brain can be divided into several functional areas. At the base is the brain stem, center for the control of cardiac and respiratory www.americanscientist.org
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Figure 5. The Utah Electrode Array provides a multichannel interface to the cerebreal cortex and peripheral nerve bundles. The silicon assembly is insulated with a biocompatible polymer, except for the tips, which are metallized with iridium oxide to enable electronic connection to the ionic environment of the nervous tissue. Each of the numerous electrodes (one hundred in the devices shown above) is individually addressable. (Images courtesy of Richard A. Normann, University of Utah.)
functions. Above the brain stem are deep structures—the thalamus, hippocampus, basal ganglia and others—that have a range of functions, from temperature regulation to emotional response to stimuli to memory formation. The cerebellum, at the lower back of the skull, receives sensory and motor input and appears to be responsible for posture and motor coordination. The higher brain functions reside in the cerebral cortex on the brain’s surface. The cortex consists of six layers, containing different cells or processes of cells that carry different kinds of information. The cortical surface is further divided into regions of functional specificity— visual cortex, auditory cortex, motor cortex and so on, each with specialized chores related to the initiation, execution or processing of neurological events. In the spinal cord, the dorsal (back) side carries sensory information, and the ventral (front) side carries motor information. Along with neurons, many other cell types inhabit the CNS, including an array of glial cells (non-neuron support
cells) that includes astrocytes, microglia, oligodendrocytes, Schwann cells and neural precursor cells. The interactions among these cells figure importantly in the response to implanted CNS interfaces. Host Response in the CNS When a device is implanted in the brain or spinal cord for extended periods, an unforgiving inflammatory response is initiated. Initial electrode insertion is likely to damage multiple structures, including capillaries, extracellular matrix and support cells such as astrocytes. Macrophages, the debris scavengers of the immune system, may enter through severed vessels. Microglia, which are debris scavengers specific to the brain, migrate to the site of the injury; staining shows them clustered around electrode interfaces. Activation of microglia is followed by encapsulation of the electrode by astrocytes, forming a dense cellular sheath that probably diminishes the ability of the electrode to record and stimulate by increasing tissue impedance. The chemical responses of the glial cells, including 2010 January–February
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production of signaling molecules and reactive oxygen species, may contribute to a decrease in the number of neurons in proximity to the electrode over time. In attempts to circumvent the host response, electrodes have been fabricated with different physical dimensions and geometries. Tip design can affect the acute (initial) response, but within a few weeks, the inflammatory response looks similar in all cases. Coating the electrodes with anti-inflammatory agents seems to inhibit glial activation, but it is not yet known whether this strategy will improve the longevity of cortical recording. Overall, it is likely that the more the glial response can
ECoG and the fidelity of a single cell, it may be desirable to address a specific localized region of the cortex. Penetrating microwire arrays such as the Utah arrays shown in Figure 5 can address single units or small regions of the brain. More physical parts protruding in the brain is inevitably accompanied by more tissue damage, but such devices have been used with success in a variety of nonhuman primate and human studies. Selectivity The neuron-packed brain and spinal cord are complex volume conductors. Signals in the CNS are typically small in amplitude and deterioriate
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body (antidromic). Cells and fibers of passage have similar thresholds for activation, and stimulation may activate both pre- and post-synaptic elements. (Communication between neurons takes place at intimate gaps between cells called synapses.) Furthermore, brain function is localized but some of the functions are coordinated over considerable physiological distances, certainly very large distances compared to implant size. In sum, the structure of the brain presents a difficult challenge when the goal is a selective neurological response. In some applications, alteration of the stimulation waveform and polarity can increase selectivity by
Figure 6. Selectivity in the neuron-packed brain is confronted by the “spaghetti and meatballs” problem, to use the parlance of graduate students. When an implant such as the micromachined device shown (above left) is placed in brain tissue, the electrodes are in close proximity to cell bodies, axons and dendrites of neurons, and stimulating currents may have different and conflicting effects on each. (Image above left courtesy of Daniel Palanker, Stanford University.)
be inhibited, the better the prognosis for long-term implants. As in the peripheral nervous system, dealing with host response in the CNS requires a tradeoff between resolution and invasiveness. Penetrating electrodes are not always necessary. For example, electrocorticogram (ECoG) electrodes are placed inside the skull but above the brain. However, the signals accessible from the brain surface are the summation of a vast number of neural signals that deliver imprecise spatial information. The ECoG is the standard tool for defining zones linked to epileptic seizure, but for many applications a higher degree of resolution may be required. Between the summed signal of an 54
rapidly over space. Stimulating electrodes are placed in proximity with cells, axons and dendrites (neuron processes that receive signals from other neurons and conduct the messages back to the cell body of the neuron). It is unclear which elements of which neurons are most responsive to stimulation. Current may activate or inactivate neurons and axons depending on morphology, distance from the electrode, orientation and other stimulus parameters. Stimulation of axons carrying longdistance messages through the brain (called fibers of passage) results in action potentials propagating in both directions, the normal direction toward the axon (orthodromic) and the reverse direction toward the cell
stimulating some neurological elements preferentially. For example, as shown in Figure 7, positive-phase waveforms selectively stimulate local cells, whereas negative-phase waveforms preferentially stimulates axons of passage. The range of stimulation patterns, including asymmetric waveforms and assorted polarity manipulations, are being evaluated to increase selectivity in both the central and peripheral nervous system. Emerging Opportunities The intimacy and density of neural interfaces promises to be dramatically increased by connections between microcircuits and single neurons or even single ion channels.
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In 2004, R. Alexander Kaul at the Max Planck Institute for Biochemistry and coworkers developed a silicon-neuron hybrid by culturing pre- and postsynaptic nerve cells on a silicon chip. The presynaptic cell was stimulated by a capacitor on the chip, leading to stimulation of the postsynaptic cell, which was recorded by a transistor on the chip. Repetitive stimulation by the capacitor strengthened the synaptic communication between the two cells, demonstrating neuronal memory on the silicon chip. The direct integration of a neuronal circuit and a semiconductor chip will likely prove to be an important step in the integration of neuroelectronic devices. A feature of the intimate contact between neuron and device on the silicon chip is that it enables capacitative stimulation by generating field effects through the accumulation of charge without the actual transfer of charge. The miniaturization of electrodes is limited by the ability to pass charge from the metal electrode to ionic carriers in tissue, which is related to the surface area of the electrode. Excess charge per unit area damages the electrode via corrosion and damages tissue via chemical reactions at the electrodetissue interface. With capacitative currents, stimulation occurs without electron transfer or chemical reactions at the electrode surface. Efforts to move the capabilities of siliconneuron hybrids from in vitro to in vivo are generating great excitement. Neurons cultured in wells on silicon-based electrodes have been shown to grow extensions away from the probe, suggesting the possibility of in vivo circuitry. An ongoing challenge is maintaining the stability of the circuit, a task that includes preventing the neurons from migrating away from the probe. A different and particularly arresting approach is the use of light to replace electrical stimulation. In classic work in the early 1970s, Richard L. Fork at Bell Laboratories demonstrated that laser illumination could produce excitation of molluscan neurons through a mechanism that was unknown at the time, and remains murky to this day. Later experiments suggest that photochemical reactions at the surfaces of neurons may generate reactive oxygen www.americanscientist.org
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Figure 7. The graph above shows the different activation patterns of cell bodies (green) and fibers (red) in response to different stimulation waveforms and patterns of polarization. Peak discrimination occurs where the vertical height between the red and green traces is greatest. Exploiting these differences may contribute to achieving selective stimulation of neuronal targets.
species that lead to depolarization, possibly coupled with photothermal injury that transiently perforates the membrane, again leading to depolarization. The intensity of light required by Fork was very high; subsequent work on focusing of the optical stimulation has brought that intensity threshold closer to biologically tolerable limits. Recently, laser illumination was used to directly excite the rat sciatic nerve, during which it was possible to grade the amplitude of the evoked muscle response by the intensity of the light. An alternative to direct optical stimulation brings in genetic engineering to create light-responsive neurons. Among the approaches being explored are the transformation of normally non-light-responsive cells by genetically linking lightsensitive molecular substituents to ion channels expressed in the cell, and engineering chemical “cages” that in response to illumination release neurotransmitters that excite neurons possessing receptors for the transmitter. These optogenetic tools, possibly linked to a fi-
ber-optic-based system for localized ilumination, offer the promise of highly selective stimulation of target cells and may form the basis for a new generation of neurotechnological solutions for research and medicine. Cultivating light responsiveness in neurons has a sound biological heritage. The retina of the eye is composed of specialized light-sensitive neurons that can become activated by as little as one photon. In 2002, Boris Zemelman and colleagues used genetic manipulation to make neurons responsive to illumination by expressing genes in cultured hippocampal neurons that coded for elements of the invertebrate retina. The expressed retinal elements produced a light-controlled excitatory current in the affected cells, just as they would in the native retina, although slowly, with latencies of one second to tens of seconds. Firing frequency increased with increases in the light intensity. This approach was extended by Matthew Banghart at the University of California and colleagues when 2010 January–February
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Figure 8. In Fall 2009 worldwide media attention swung to the SmartHand Project, which has developed an experimental prosthetic hand with an astonishing degree of motor control and the ability to simulate touch sensitivity by communicating with servomotor transducers affixed higher up the arm. The current generation of the SmartHand uses skin electrodes rather than implanted interfaces to send and receive messages. Upcoming is a plan to integrate some of the message and control functions of the SmartHand with implanted interfaces like those described in this article. (The SmartHand is a joint project of Lund University in Sweden, Scuola Superiore Sant’Anna in Italy, Aalborg University in Denmark, Tel Aviv University in Israel, Tyndall Institute in Ireland, Össur corporation in Iceland, and SciTech in Sweden, funded by the European Commission, Framework Programme 6. Image courtesy of ARTS Lab, Scuola Superiore Sant’Anna.)
they developed a potassium channel that opened and closed in response to different wavelengths of light. The channel was joined with a photosensitive molecule (azobenzene) whose conformation determined whether an attached molecule could reach the channel and block it. After expressing the engineered channels in neurons from rat hippocampus, ultraviolet light of 390 nanometers in wavelength caused a conformation change in the azobenzene that removed the channel blocker and allowed the outflow 56
of potassium. Visible green light at 500 nanometers altered the shape of the azobenzene, and blockage of the channel was restored. A photoswitch like this could someday be used to restore photoreceptor-like function in cases of retinitis pigmentosa, a group of conditions in which disorders of the retinal photoreceptors (the light-sensitive rod and cone cells of the retina) lead to blindness. This would be an alternative to recent, highly publicized work in the development of visual prosthetics that capture scenes like
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a camera and directly stimulate retinal or cortical neurons to replace the signal normally received from photoreceptors. The power of genetic approaches was seen in 2006 when Anding Bi at Wayne State University and colleagues achieved long-term expression of an algal light-sensitive protein in the inner retinal neurons (nonphotoreceptor cells) of the rat. The transformed neurons responded to illumination as photoreceptors would, with membrane depolarization and light-induced action potentials. The researchers later demonstrated that light stimuli evoked potentials in the visual cortex comparable in amplitude to those evoked in control animals. These results demonstrate the feasibility of genetically transformed cells as a technique for neural interfacing and potentially for medical rehabilitation. The potential advantages of optical stimulation include selectively activating only targeted neurons, eliminating electrical artifacts that complicate recording of neuronal activity in the presence of electrical stimulation, and eliminating the electrochemical reactions at the interface of electrode tip and tissue that lead to electrode decay and tissue damage. But the challenges are many. The ability to adequately express inserted proteins over the long term is still developing, and doing so in specific subsets of neurons is a daunting task. A fiber-optic-based system for selective neural stimulation holds great appeal, although it will retain some of the problems of invasiveness of electrodes and will be constrained by the same intensity-distance relationship of conventional electrical stimulation, with the robustness of neuronal activation droppping off quickly with the distance from the light source. Integration of external electronics and the nervous system has immense potential to advance our understanding of the nervous system and the brain and will certainly be transformative for the lives of individuals with compromised neural function due to disease or injury. In the short term, individuals are already regaining some measure of control over lost motor functions and benefiting from better management of maladies like
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Parkinson’s disease and epilepsy. In the long term, we can envision exquisitely sensitive research and diagnostic tools and neural-electronic hybrid prosthetics that rival the endowments of a sound body. Bibliography Arenkiel, B. R., J. Peca, I. G. Davison, C. Feliciano, K. Deisseroth, et al. 2007. In vivo light-induced activation of neural circuitry in transgenic mice expressing channelrhodopsin-2. Neuron 54:205–18. Banghart, M., K. Borges, E. Isacoff, D. Trauner and R.H. Kramer. 2004. Light-activated ion channels for remote control of neuronal firing. Nature Neuroscience 7:1381–86. Bi, A.D., J. J. Cui, Y. P. Ma, E. Olshevskaya, M.L. Pu, et al. 2006. Ectopic expression of a microbial-type rhodopsin restores visual responses in mice with photoreceptor degeneration. Neuron 50:23–33. Butson, C. R., and C. C. McIntyre. 2006. Role of electrode design on the volume of tissue activated during deep brain stimulation. Journal of Neural Engineering 3:1–8. Fork, R. L. 1971. Laser stimulation of nerve cells in aplysia. Science 171:907–8. Grill, W. M., S. E. Norman and R. V. Bellamkonda. 2009. Implanted neural interfaces.
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Annual Review of Biomedical Engineering 11:1–24. Hansen M., M. K. Haugland and A. Sinkjaer. 2004. Evaluating robustness of gait event detection based on machine learning and natural sensors. Transactions on Neural Systems and Rehabilitation Engineering 12:81–88. Hoffer, J. A., and K. Kallesoe. 2001. How to use nerve cuffs to stimulate, record, or modulate neural activity. In Neural Prostheses for Restoration of Sensory and Motor Function, eds. J. K. Chapin and K. A. Moxon. Boca Raton, FL: CRC Press. Pp. 139–78. Kaul, R. A., N. I. Syed and P. Fromherz. 2004. Neuron-semiconductor chip with chemical synapse between identified neurons. Physical Review Letters 92:4. Kim, Y. T., V. K. Haftel, S. Kumar and R. V. Bellamkonda. 2008. The role of aligned polymer fiber-based constructs in the bridging of long peripheral nerve gaps. Biomaterials 29:3117–27. McDonnall, D., G. A. Clark and K. A. Normann. 2004. Interleaved, multisite electrical stimulation of cat sciatic nerve produces fatigue-resistant, ripple-free motor responses. Transactions on Neural Systems and Rehabilitation Engineering 12:208–15. Polasek, K.H., H.A. Hoyen, M.W. Keith and D.J. Tyler. 2007. Human nerve stimulation thresholds and selectivity using a multicontact nerve cuff electrode. Transactions on
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Neural Systems and Rehabilitation Engineering 15:76–82. Santhanam, G., S. I. Ryu, B. M. Yu, A. Afshar and K. V Shenoy. 2006. A high-performance brain-computer interface. Nature 442:195– 98. Schwartz, A. B., X. T. Cui, D. J. Weber and D. W. Moran. 2006. Brain-controlled interfaces: movement restoration with neural prosthetics. Neuron 52:205–20. Zemelman, B. V., G. A. Lee, M. Ng and G. Miesenbock. 2002. Selective photostimulation of genetically ChARGed neurons. Neuron 33:15–22r. Zhong, Y. H., and R. V. Bellamkonda. 2007. Dexamethasone-coated neural probes elicit attenuated inflammatory response and neuronal loss compared to uncoated neural probes. Brain Research 1148:15–27.
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Carbon Dioxide and the Climate Gilbert N. Plass
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Editor’s note: The text of the original article ran to more than 6,000 words covering 15 pages—too much to be included here. Elisions are noted by three asterisks. The full text, as well as a recreation of an associated graph, can be found online at the link listed on page 67. 58
cientists have long been fascinated with the problem of explaining variations in the climate. For at least nine-tenths of the time since the beginning of recorded geological history, the average temperature of the Earth has been higher than it is today. Between these warm epochs there have been severe periods of glaciation which have lasted a few million years and which have occurred at intervals of roughly 250,000,000 years. Of more immediate interest to us is the general warming of the climate that has taken place in the last sixty years. Theories of climatic change are exceedingly numerous. Is it possible that any of these theories can explain most of the known facts about climate? The most widely held theories at the present time call upon variations in the solar energy received by the earth, changes in the amount of volcanic dust in the atmosphere, and variations in the average elevation of the continents. Although it is entirely possible that changes in each of these factors may have had an influence on the Earth’s climate at particular times and places, none of these theories alone seems able to explain a majority of the known facts about world-wide climatic variations. Although the carbon dioxide theory of climatic change was one of the most widely held fifty years ago, in recent years it has had relatively few adherents. However, recent research work suggests that the usual reasons for rejecting this theory are not valid. Thus it seems appropriate to reconsider the question of variations in the amount of carbon dioxide in the atmosphere and whether it can satisfactorily account for many of the world-wide climatic changes. Because of the relatively low temperatures at the Earth’s surface and in the atmosphere, virtually all of the outgoing radiation from the Earth to space is in the infrared region of the spectrum. Thus it is important to know which constituents of the atmosphere absorb in the infrared. The three most abundant gases in our atmosphere are oxygen, nitrogen, and argon. However, none of these three gases absorb appreciably in the relevant spectral region in the infrared. If these were the only gases in our atmosphere, our climate would be considerably colder than it is today. The heat radiated from
the surface of the Earth would not be stopped in its passage out to space with the result that the Earth’s surface would cool rapidly. Fortunately for us, three other gases occur in our atmosphere in relatively minute quantities: carbon dioxide, water vapor, and ozone. Unlike the more abundant gases, all three of these rarer gases absorb strongly over at least a portion of the infrared spectrum. The concentration of carbon dioxide in the atmosphere is about 0.03 per cent by volume, it is fairly uniformly mixed as high as accurate measurements have been made. Water vapor and ozone also exist in very small concentrations in the atmosphere, but the exact amount that is present varies with time and place. The infrared absorption properties of carbon dioxide, water vapor, and ozone determine our climate to a large extent. Their action has often been compared to that of a greenhouse. There the rays of the sun bring the heat energy in through the transparent glass. However, the outgoing heat energy from the plants and other objects in the greenhouse is in the infrared where glass is largely opaque. The heat energy is fairly effectively trapped inside the greenhouse and the temperature is considerably warmer than outside. In a similar manner the temperature at the surface of the Earth is controlled by the transparency of the atmosphere in the visible and infrared portions of the spectrum. The incoming radiation from the sun in the visible portion of the spectrum reaches the surface of the Earth on a clear day with relatively little attenuation since the atmosphere is transparent to most frequencies in the visible. However, in order to have a warm climate, this heat energy must be held near the surface of the Earth and cannot be reradiated to space immediately. The atmosphere is opaque or partially opaque to a large range of frequencies in the infrared because of the absorption properties of the three relatively rare gases described above. Thus radiation emitted by the Earth’s surface cannot escape freely to space and the temperature at the surface is higher than it would be otherwise. The atmosphere has just the same properties as the glass in the greenhouse.
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Gilbert N. Plass, circa 1955. (From Hodges Photographers, courtesy of AIP Emilio Segré Visual Archives.)
The carbon dioxide theory states that, as the amount of carbon dioxide increases, the atmosphere becomes opaque over a larger frequency interval; the outgoing radiation is trapped more effectively near the Earth’s surface and the temperature rises. The latest calculations show that if the carbon dioxide content of the atmosphere should double, the surface temperature would rise 3.6 degrees Celsius and if the amount should be cut in half, the surface temperature would fall 3.8 degrees. The carbon dioxide theory was first proposed in 1861 by Tyndall. The first extensive calculations were necessarily done by very approximate www.americanscientist.org
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methods. There are thousands of spectral lines due to carbon dioxide which are responsible for the absorption and each of these lines occurs in a complicated pattern with variations in intensity and the width of the spectral lines. Further the pattern is not even the same at all heights in the atmosphere, since the width and intensity of the spectral lines varies with the temperature and pressure. Only recently has a reasonably accurate solution to the problem of the influence of carbon dioxide on surface temperature been possible, because of accurate infrared measurements, theoretical developments, and the availability of a high-speed electronic computer. 2010
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The fact that water vapor absorbs to some extent in the same spectral interval as carbon dioxide is the basis for the usual objection to the carbon dioxide theory. According to this argument the water vapor absorption is so large that there would be virtually no change in the outgoing radiation if the carbon dioxide concentration should change. However, this conclusion was based on early, very approximate treatments of the very complex problem of the cal-
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culation of the infrared flux in the atmosphere. Recent and more accurate calculations that take into account the detailed structure of the spectra of these two gases show that they are relatively independent of one another in their influence on the infrared absorption. There are two main reasons for this result: (1) there is no correlation between the frequencies of the spectral lines for carbon dioxide and water vapor and so the lines do not often overlap because of nearly co-
Gilbert N. Plass: Climate Science in Perspective James Rodger Fleming
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ilbert Plass was a scientist on the cutting edge of climate research in 1956. His article in American Scientist, on the recently revived carbon dioxide theory of climate change, and the role that the combustion of fossil fuel was playing in it, was aimed at a broadly educated scientific readership; it was one of six related articles he published that year and one of about a dozen he published that decade. In a 1997 interview, Plass told me, “all sorts of things came together” that placed him at the scientific forefront: new detailed laboratory measurements of the absorption bands of water vapor, carbon dioxide and ozone; theoretical developments involving the influence of temperature and pressure on infrared absorption; new information about the carbon cycle and industrial emissions; and access to a new high-speed electronic computer to facilitate complex calculations of radiative transfer that replaced the older, graphical approximations. Gilbert Norman Plass was born in Toronto, Ontario, Canada, on March 22, 1920. He was a physicist who developed an early computer model of infrared radiative transfer and published a number of articles on carbon dioxide and climate between 1953 and 1959. He received a B.S. from Harvard University in 1941, where he recalled that his courses on geology, chemistry and physics provided an interdisciplinary foundation for his later work. He was particularly impressed by the experimental techniques of John Strong, one of his physics professors. Plass received his Ph.D. from Princeton University in 1947 and worked as an associate physicist at the Metallurgical Laboratory (Manhattan District) of the University of Chicago from 1942
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to 1945. He became an instructor of physics at Johns Hopkins University in 1946 and was subsequently promoted to assistant and then associate professor. At Hopkins he conducted research on infrared radiation with funds provided by the Office of Naval Research. During his sabbatical year, at Michigan State University in 1954–55, he gained access to a large computer and realized it offered the perfect way to construct a better model of radiative transfer. In 1955 Plass moved out of academics, serving for a year as a staff scientist with Lockheed Aircraft Corporation. He then joined the advanced research staff of the Aeronutronic division of the Ford Motor Company. Ford provided him with excellent laboratory facilities where he could continue his experimental work on infrared physics. In 1960, he became manager of the research lab at Ford’s theoretical physics department and a consulting editor of the journal Infrared Physics. In 1963, he accepted a position as the first professor of atmospheric and space science at the Southwest Center for Advanced Studies (now the University of Texas, Arlington) where he remained for five years. In 1968, he arrived at Texas A&M University, where he served as professor of physics and head of the department. He is the author of six books, including Infrared Physics and Engineering (1963) and more than 100 articles on radiative transfer and climate change, nuclear fission and neutron physics, electromagnetic and gravitational action at a distance, electron emission, and electrostatic electron lenses. Plass and his spouse were active supporters of the arts, helping to establish and direct arts societies and producing a radio program in Texas.
He passed away in Bryan, Texas, on March 1, 2004. In 1956 Gilbert Plass was heir to a century of work that identified variations in the trace amounts of carbon dioxide in the atmosphere as a possible cause of ice ages and interglacial periods. John Tyndall wrote in 1861 that slight changes in the amount of any of the radiatively active constituents of the atmosphere—water vapor, carbon dioxide, ozone or hydrocarbons—may have produced “all the mutations of climate which the researches of geologists reveal … they constitute true causes, the extent alone of the operation remaining doubtful.” Thirty-five years later Svante Arrhenius published a landmark paper examining the effect of different concentrations of atmospheric CO2 on the temperature of Earth. His energy budget model, which he calculated by hand, contained estimates of the absorption and emission of terrestrial radiation by water vapor and carbon dioxide, but since infrared research was in its infancy then, Arrhenius had access to only very limited spectroscopic data. Because of these limitations, the carbon dioxide theory of climate change was in deep eclipse in 1938 when British scientist and engineer Guy Stewart Callendar revived it and placed it on a firm scientific basis. Callendar documented a significant upward trend in temperatures for the first four decades of the 20th century and noted the systematic retreat of glaciers. He compiled estimates of rising concentrations of atmospheric CO2 since pre-industrial times and linked the rise of CO2 to the combustion of fossil fuel. Finally, he synthesized information newly available concerning the infrared absorption bands of trace atmospheric constitu-
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incident positions for the spectral lines; (2) the fractional concentration of water vapor falls off very rapidly with height whereas carbon dioxide is nearly uniformly distributed. Because of this last fact, even if the water vapor absorption were larger than that of carbon dioxide in a certain spectral interval at the surface of the Earth, at only a short distance above the ground the carbon dioxide absorption would be considerably larger than that of the water vapor. Careful
ents and linked increased sky radiation from increased CO2 concentrations to the rising temperature trend. Today this is called The Callendar Effect. Building on such foundations, Plass was able to take the next steps in research and provide his masterful overview of the carbon dioxide theory and its implications for the future. He established connections between the physics of infrared absorption by gases, the geochemistry of the carbon cycle, feedback loops in the climate system and computer modeling. Using recent measurements of the influence of the 15micrometer CO2 absorption band, Plass calculated a 3.6 degrees Celsius surface temperature increase for doubling of atmospheric carbon dioxide and a 3.8 degree decrease if the concentration were halved. Contrary to the assumptions of many scientists at the time, the effect of water vapor absorption did not mask the carbon dioxide effect by any means. He used these results to argue for the applicability of the carbon dioxide theory of climate change for geological epochs and in recent decades. Stressing the intrinsic role carbon dioxide plays in our atmosphere, Plass discussed the danger of fossil fuel burning and deforestation. The six billion tons of CO2 being added to the atmosphere each year was sufficient to cause noticeable changes in the Earth’s radiation balance and thus the climate. He noted that the observed 1.1 degree rate of climate warming per century was in agreement with the predictions of the carbon dioxide theory. Waxing prophetic, Plass wrote that the oceans would be able to sequester only a small amount of the anthropogenic carbon, leaving the majority in the atmosphere. Accumulating atmospheric CO2 content from fossil fuel-based industrial activities would eventually result in a temperature rise of at least 7 degrees. Plass held out little hope for nuclear power—expressing an opinion www.americanscientist.org
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estimates show that the temperature changes given above for carbon dioxide would not be reduced by more than 20 per cent because of water vapor absorption. One further objection has been raised to the carbon dioxide theory: the atmosphere is completely opaque at the center of the carbon dioxide band and therefore there is no change in the absorption as the carbon dioxide amount varies. This is entirely true for a spectral inter-
that would not be widespread for several more decades. Presaging the work of Charles David Keeling, which began two years later, Plass called for new accurate measurements of the increasing CO2 concentration in the atmosphere, which he rightly estimated should be on the order of 0.3 percent per year. Plass pointed out that humanity was conducting a large-scale experiment on the atmosphere, the results of which would not be available for several generations: “If at the end of this century, the average temperature has continued to rise and in addition measurement shows that the atmospheric carbon dioxide amount has also increased, it will be firmly established that carbon dioxide is a determining factor in causing climatic change.” There have been two interruptions (pauses, if you will) in the rise of global average temperature since 1956, and of course, Earth’s climate is influenced by more than just CO2. Other trace gases and black carbon warm the climate, and aerosols cool it. On a larger scale, the astronomical theory of orbital influences was revived circa 1976, and climate variation attributed to such factors as ENSO, the Pacific Decadal Oscillation, and solar activity (or the lack thereof) are now being widely discussed. Still, more than 50 years later, scientists agree that the uncontrolled experiment pointed out by Plass in 1956 has been verified, and a warmer future caused by the radiative effects of CO2 is in store. The cutting edge question now is, What to do about it? Bibliography Arrhenius, Svante. 1896. On the influence of carbonic acid in the air upon the temperature of the ground. Philosophical Magazine, series 5, 4:237–276. Callendar, G. S. 1938. The artificial production of carbon dioxide and its influence on temperature. Quarterly Journal of the Royal Meteorological Society 64:223–240. Callendar, G. S. 1949. Can carbon dioxide influence climate? Weather 4:310–314.
Fleming, James Rodger. 1998, 2005. Historical perspectives on climate change. New York: Oxford Univeristy Press. Fleming, James Rodger. 2007. The Callendar Effect: The Life and Work of Guy Stewart Callendar (1898–1964), the Scientist Who Established the Carbon Dioxide Theory of Climate Change. Boston: American Meteorological Society. Plass, Gilbert N. 1953. The carbon dioxide theory of climatic change. Bulletin of the American Meteorological Society 34:80. Plass, Gilbert N. 1956a. Carbon dioxide and the climate. American Scientist 44:302–316. Plass, Gilbert N. 1956b. The influence of the 9.6 micron ozone band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82:30–44. Plass, Gilbert N. 1956c. The influence of the 15μ carbon-dioxide band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82:310–324. Plass, Gilbert N. 1956d. The carbon dioxide theory of climatic change. Tellus 8:140–154. Plass, Gilbert N. 1956e. Infrared radiation in the atmosphere. American Journal of Physics 24:303–321. Plass, Gilbert N. 1956f. Effect of carbon dioxide variations on climate. American Journal of Physics 24:376–387. Plass, Gilbert N. 1959. Carbon dioxide and climate. Scientific American, July, 41–47. Plass, Gilbert N., and D. I. Fivel. 1955a. A method for the integration of the radiativetransfer equation. Journal of Meteorology 12:191–200. Plass, Gilbert N., and D. I. Fivel 1955b. The influence of variable mixing ratio and temperature on the radiation flux. Quarterly Journal of the Royal Meteorological Society (81)48–62. Tyndall, John. 1861. On the absorption and radiation of heat by gases and vapours, and on the physical connection of radiation, absorption, and conduction. Philosophical Magazine, series 4, 22:169–194, 273–285. James Rodger Fleming is Professor of Science, Technology and Society at Colby College, Maine. He is the founder and first president of the International Commission on History of Meteorology, editor-in-chief of History of Meteorology, domain editor for Wiley Interdisciplinary Reviews on Climate and a series editor for Palgrave Studies in the History of Science and Technology. In addition to listings in the bibliography, his books include Fixing the Sky: The Checkered History of Weather and Climate Control and Meteorology in America, 1800–1870. 2010
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val about one micron wide on either side of the center of the carbon dioxide band. However, the argument neglects the hundreds of spectral lines from carbon dioxide that are outside this interval of complete absorption. The change in absorption for a given variation in carbon dioxide amount is greatest for a spectral interval that is only partially opaque; the temperature variation at the surface of the Earth is determined by the change in absorption of such intervals. Thus there does not seem to be a fundamental objection to the carbon dioxide theory of climate change. Further the temperature changes given by the theory for reasonable variations in the carbon dioxide amount are more than enough to cause noticeable changes in the climate. It is not usually appreciated that very small changes in the average temperature can have an appreciable influence on the climate. For example, various authorities estimate that, if the average temperature should decrease from 1.5 to 8 degrees, the glaciers would again form over an appreciable fraction of the Earth’s surface. Similarly a rise in the average temperature of perhaps only 4 degrees would bring a tropical climate to most of the Earth’s surface. Before discussing in detail the carbon dioxide theory of climatic change it is first necessary to study the various factors that enter into the carbon dioxide balance, including the exchange of carbon dioxide between the oceans and the atmosphere. The largest loss of carbon dioxide from the atmosphere is due to the process of photosynthesis which uses about 60 x 109 tons per year. 62
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In a steady state precisely the same amount of carbon dioxide is returned to the atmosphere each year by all the processes of respiration and decay of plants and animals, provided only that none is permanently lost in the form of new coal, oil, and other organic deposits. At the present time, at least, this loss is very small (0.01 x 109 tons per year) and can be neglected for all practical purposes. If this steady state of absorption and emission of carbon dioxide by the organic world is disturbed, for example, by a sudden increase of carbon dioxide in the atmosphere, it is known that the amount used in photosynthesis would then increase. However, after a very few years the processes of decay and respiration would also have increased. Since an average carbon atom that has been used in photosynthesis returns to the atmosphere from the biosphere within about 10 years, and virtually all of the carbon atoms return within 250 years it follows that the factors influencing the carbon dioxide balance from the organic world would again be in balance in a very few years. The two most important contributing factors from the inorganic world are the release of carbon dioxide from the interior of the Earth by hot springs, volcanoes, and other sources and the formation of carbonates in the weathering of igneous rocks. They happen to be nearly in balance today. The first one adds and the second subtracts about 0.1 x 109 tons per year to the atmosphere. Thus it appears that as far as natural factors are concerned, the amount of carbon dioxide taken out of the atmosphere is very nearly equal to the amount returned to it. The specific
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numbers given in this section are only order of magnitude estimates. The values given here are averages of some of the more careful estimates. Recently, however, man has added an important new factor to the carbon dioxide balance. As first pointed out by Callendar, the combustion of fossil fuels is adding 6.0 x 109 tons per year of carbon dioxide to the atmosphere at the present time and the rate is increasing every year. Today this factor is larger than any contribution from the inorganic world. Thus today man by his own activities is increasing the carbon dioxide in the atmosphere at the rate of 30 per cent a century. The possible influence of this on the climate will be discussed later. The oceans contain a vast reservoir of carbon dioxide; some of it is in the form of dissolved gas, but it consists mostly of carbonates in various degrees of ionization. From the known dissociation constants for sea water, it is possible to calculate the atmospheric carbon dioxide pressure that is in equilibrium with a given amount of carbonates in the oceans. At the present time the carbon dioxide pressure is about 3 x 10–4 atmospheres; there are 2.3 x 1012 tons of carbon dioxide in the atmosphere and 130 x 1012 tons of carbon dioxide and carbonates in the oceans. Thus the oceans contain over fifty times as much carbon dioxide as the atmosphere. If conditions should change, the oceans can add to or subtract from the amount in the atmosphere. Kulp has recently shown from radiocarbon determination that the deep ocean waters at the latitude of Newfoundland were at the surface 1,700 years ago. This suggests that it may take www.americanscientist.org
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tens of thousands of years for the waters of the deep ocean to make one complete circuit from the surface to the bottom and back. Only the surface waters of the oceans can absorb carbon dioxide directly from the atmosphere. Since there is very little circulation between the surface waters and the ocean depths, the time for the atmosphere-ocean system to return to equilibrium following a disturbance of some sort is at least as long as the turnover time of the oceans. Thus, if the atmospheric carbon dioxide amount should suddenly increase, it may easily take a period of tens of thousands of years before the atmosphere-ocean system is again in equilibrium. *** What is the reason for the recent temperature rise that is found throughout the world? Will this trend toward warmer climates continue for some time? The carbon dioxide theory may provide the answer. We have discussed the burning of fossil fuels which is adding more than 6 x 109 tons per year of carbon dioxide to the atmosphere. If all of this extra carbon dioxide remains in the atmosphere, the average temperature is increasing at the rate of 1.1 degrees per century from this cause. Since 1900 a careful study of world temperature records shows that the average temperature has been increasing at roughly this rate. Of course, the agreement between these two numbers could be merely a coincidence. As the concentration of carbon dioxide in the atmosphere increases, there are two factors in 2010
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the carbon dioxide balance than can change. First the oceans absorb more carbon dioxide to come to equilibrium with the larger atmospheric concentration. However, only the surface waters can absorb this gas and because of the slow circulation of the oceans, it probably takes at least ten thousand years for this process to come to equilibrium. Whenever the carbon dioxide amount is increasing an upper limit for the amount absorbed by the oceans can be found at any time by assuming the atmosphereocean system is always in equilibrium. The ac-
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tual amount absorbed by the oceans will be considerably less than the amount calculated in this manner for at least several centuries after a sudden increase in the atmospheric carbon dioxide amount. In the first few centuries the surface ocean waters can absorb only a relatively small fraction of the additional carbon dioxide. The second factor that can change is the amount used in photosynthesis. A higher level of photosynthetic activity can be supported by the increased carbon dioxide amount. As previously discussed, this process temporarily
Does Science Progress? Gilbert Plass Redux Gavin Schmidt
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onsidering today’s concerns about human-driven climate change and the need to cut carbon emissions, it’s interesting to look back at a time (not that long ago) when the idea that carbon dioxide (CO2) affected climate was very much a fringe concern. Gilbert N. Plass’s 1956 article (reprinted in this issue of American Scientist) was only the start of a quite rocky road to modern respectability for an idea born in the 19th century; even he might be surprised to see how it has become completely mainstream (despite what one might read on the Internet!). This paper, the insights it contained, and the calculations and forecasts it made actually constitute a great example of how, despite reaching bottom-line conclusions very similar to pronouncements made in the recent Intergovernmental Panel on Climate Change (IPCC) report, the science that underlies those conclusions has improved remarkably. It is also a great example of the role luck plays in determining one’s role in scientific prosperity (but more on that below). Before discussing the detail of what was in that paper, it is worth pointing out what Plass could not have known. He did not know how fast CO2 was accumulating in the atmosphere—Charles Keeling would start his seminal measurements at Mauna Loa only in 1957. Neither did he know how CO2 had varied in the past—the first ice core results only emerged in the 1980s. But he was still able, with his understanding of infrared spectroscopy, to write a paper that qualitatively predicted both these results—although with methods that we can now recognise as being incomplete—and cor64
rectly concluded that the impact of CO2 on climate would be clear by the end of the 20th century. There are other things that we know now that he could not possibly have known—the importance of other greenhouse gases (methane in particular, which wasn’t recognised as an important contributor to anthropogenic forcing until 1974, but also chlorofluorocarbons and N2O, which have also increased dramatically because of human influence) and the role of human-emitted particulates and low-level ozone precursors. To be sure, there is much that marks the paper out as a product of its era: There is an excessive focus on single-factor explanations of all climate changes and a penchant for what would now be considered naive back-of-the-envelope estimates of the impacts of small changes on very complex systems. And as befits publication in a popular science magazine, there is a lot of big-picture discussion, although perhaps in excess of what would be considered prudent today. The paper revolves around three main themes: the modern day carbon cycle and the fate of human-produced CO2, the calculation of the radiative impact of that CO2 and the resulting temperature rise, and the possibilities for CO2 playing a role in climate changes in the past. I’ll review the first two of these themes and leave the far more speculative discussions about the cause of the ice ages for another time. Plass knew that atmospheric levels of CO2 were around 300 parts per million by volume (ppmv) and correctly noted (as had Guy Stewart Callendar almost 20 years earlier) that human use
of fossil fuel would lead to an increase in atmospheric levels of CO2. He was actually a little optimistic, though, in assuming that only 6 × 109 tons of CO2 per year (equivalent to 1.5 gigatonnes of carbon per year, or GtC/yr) were being emitted. Current estimates suggest that emissions in 1956 were already almost 50 percent higher than that (8.8 × 109 tons CO2 /yr or 2.2 GtC/yr). He also understood enough of the terrestrial and oceanic carbon cycle to know that uptake of the anthropogenic carbon would be slow. He had two quite telling insights: First, although the residence time for carbon dioxide in the atmosphere (the total amount of CO2 divided by the flux in and out of the ocean) is on the order of a few years, the perturbation time is much longer— even up to a few tens of thousands of years—because of the slow uptake in the deep ocean and the buffering effects of the ocean chemistry. Second, he realised that the added carbon in the ocean would cause increasing acidification with consequent impacts on marine life (although he did underestimate how big this effect would be). Combining the rate of increase of fossil carbon and lack of uptake in the ocean, he estimated that the CO2 levels might increase 30 percent in a century. Since 1850, CO2 has actually increased by more than 100 ppmv (36 percent above pre-industrial values), and so this appears to be a reasonable prediction. However, Plass was lucky. In underestimating both the current anthropogenic emissions and the uptake by the ocean, his two errors roughly cancelled. Plass’s real contribution, however, is in his assessment of what that ex-
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withdraws some of the additional carbon dioxide from the atmosphere into the organic world. However, in a relatively few years the increased rates of respiration and decay bring this process back into equilibrium and only a relatively small amount of carbon dioxide is permanently lost from the atmosphere. Thus it appears that a major fraction of the additional carbon dioxide that is released into the atmosphere remains there for at least several centuries. Even if there may be some question as to whether or not the general amelioration of the
tra CO2 would do to the climate. His calculations included the fact that you have to consider the whole atmospheric column, and that despite the large amount of water vapor near the surface, there are always large parts of the atmosphere where CO2 is a very important absorber and emitter. This meant that the impact of changing CO2 would not be as negligible as had been thought over previous decades. These calculations require good knowledge of how all the various wavelengths are absorbed by each component in the atmosphere (including clouds), and how that changes as a function of temperature and (most importantly) pressure. The data for these absorption spectra have improved enormously in the past 50 years as has the capacity to do all these calculations, so one might anticipate that this is where Plass would have been most overtaken by scientific progress. However, Plass actually did a pretty good job. Converting to more modern units and doing a little publication archaeology, we can see that he estimated the radiative forcing by a doubling of CO2 in clear sky conditions at 8.3 watts per square meter (W/m2) and that in cloudy conditions it would be 5.8 W/m2. The accepted value for the global average today is around 4 W/m2 with about a 10 percent uncertainty (including both cloudy and clear-sky conditions). Thus while his numbers were a little large, they were within a factor of two of the right answer, and much closer than the near-zero impact that had been previously considered to be the best estimate. To convert the radiative forcing into a temperature change, Plass relied on a conversion factor of about 0.43°C/(W/ m2) (again, updated to more modern units). This was not independently calculated by him and referred only to the “no-feedback” case where all other atwww.americanscientist.org
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climate in the last fifty years has really been caused by increased industrial activity, there can be no doubt that this will become an increasingly serious problem as the level of industrial activity increases. In a few centuries the amount of carbon dioxide released into the atmosphere will have become so large that it will have a profound influence on our climate. After making allowance for industrial growth, a conservative estimate shows that the known reserves of coal and oil will be used up in about 1,000 years. If this occurs, nearly 4 × 1013 tons
mospheric components (for example, water vapor and clouds) stayed the same. Modern estimates for the nofeedback sensitivity are a little lower (around 0.3°C/(W/m2)). The basis of his 3.6°C change for a doubling of CO2 is then seen as a combination of his over estimated forcing and a slightly high no-feedback sensitivity. Modern estimates of this number are around 1.2°C. Plass was aware of the potential for amplifying feedbacks, particularly via water vapor and cloud changes, but the quantification of these effects would have to wait another 10 years for the work of Fritz Möller and subsequently Suki Manabe and colleagues. Thus even though the headline number in the Plass article is well within the range of the modern IPCC reports (which give a total sensitivity of between 2 to 4.5°C for a doubling of CO2), it isn’t quite fair to give him full credit since his number doesn’t include many important factors that he was not able to quantify. Nonetheless, he realized full well the importance of numerical computation for these estimates but was working at the edge of what was then possible. Similarly, his estimate for the temperature change for the 20th century of 1.1°C was uncannily close to the actual change of roughly 0.7°C. However, as he himself admits, this “could merely be coincidence,” and unfortunately I have to confirm that. Two other factors that he was not really aware of complicate this estimate dramatically. The first is the thermal lag of the system due to the heat capacity of the oceans. This delays substantially (by decades to centuries) the full impact of a change in greenhouse gases, as it takes a long time for the ocean surface temperatures to equilibrate with the new radiation balance. Secondly, he probably wasn’t aware that other aspects of atmospheric
composition—as mentioned above— were being greatly affected by human activity as well. Nonetheless, a number of conclusions that he drew were almost prophetic. He was correct in assuming (against the conventional wisdom of his time) that moves towards nuclear energy would not make a substantial difference to carbon emissions. He was also correct in thinking that the price of removing the carbon from the air would be prohibitively expensive (as it has turned out, although some progress is being made). So does science progress? Yes, of course. Gilbert Plass had the right framework for this problem and foresaw most of the issues, but the detailed rendering of the calculations—for the carbon cycle, for the radiative transfer, for the existence of feedbacks, for the temperature response—have all become much more sophisticated and complete. What once were rough estimates have been much more tightly constrained. Speculations about growth rates and past behavior have been confirmed by multiple observations. Nonetheless, the coincidences of some of his numbers and the ones we know today are just that, coincidences, and so some part of the high regard in which we hold Plass today may simply be due to luck. Indeed, Lewis Kaplan, the author of a subsequent and more accurate calculation, has been all but forgotten since he incorrectly concluded that CO2 could not play a role in climate change. In 50 years time if someone reviews my work, I would hope to have been as lucky as Gilbert Plass. Gavin Schmidt is a climate modeller at the NASA Goddard Institute for Space Studies and coauthor of the book Climate Change: Picturing the Science, published this year by W. W. Norton. 2010 January–February
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of carbon dioxide will have been added to the atmosphere; this is seventeen times the present amount. The total amount in the atmosphereocean system will have increased from 1.32 x 1014 tons to 1.72 x 1014 tons. Even if the atmosphere-ocean system is assumed to be in equilibrium at the end of the thousand year period, the atmospheric carbon dioxide pressure will be 3 x 10–3 atmospheres, which is 10 times the present value; the corresponding increase in the temperature from this cause will be 13.4 degrees. If it is further assumed that there would be sufficient time for the calcium carbonate to dissolve and come to equilibrium in the oceans, the atmospheric pressure will be 1.1 x 10–3 atmospheres and the temperature rise 7.0 degrees. The last figure is a lower limit for the temperature rise that will occur because of man’s industrial activities; the actual temperature rise must be larger since there will be insufficient time for these various equilibria to be established. Our energy requirements are increasing so rapidly that the use of nuclear fuels will probably not change materially the rate of use of the organic fuels. Unfortunately it is difficult to obtain any direct evidence for the carbon dioxide content of the atmosphere during past geological epochs. In fact it is not even certain from direct measurements whether or not the carbon dioxide content has increased in the last 50 years. A plot of such measurements can be fitted nicely with a linear curve that increases by 10 per cent in that time interval. However, the probable error for most of the measurements is so large that this result is not very firmly established. Because of its importance to the climate, regular measurements of the atmospheric carbon dioxide content should be started at several different country locations and continued for a number of decades. Since the atmospheric carbon dioxide content varies somewhat with the past history of the air mass and the time of year, a number of measurements are necessary in order to obtain a reliable average. The present predicted rise of 3 per cent a decade could be easily observed with the present techniques of analysis. As to the carbon dioxide content of the atmosphere at earlier periods, only general discussions of the various factors that affect the carbon dioxide balance can be given at the present time. It is possible though that we will be able to calculate the carbon dioxide amount of a past epoch from measurements of the ocean temperature and the rate of carbonate deposition during that epoch together with further studies of the atmosphere-ocean equilibrium. *** Further evidence as to the carbon dioxide amounts in the past is provided by the pH of sea water. There is a definite pH value associated with a given atmospheric carbon dioxide 66
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amount when the atmosphere-ocean system is in equilibrium. Further, many marine animals are very sensitive to the pH value, the higher marine animals being more sensitive in general than the lower. For example, herring are killed if the pH changes by more than one-half unit; lower marine animals such as sea urchins, diatoms, and algae cannot tolerate pH changes of more than one unit. This suggests that the pH of the oceans has not varied by more than these amounts since the time when these animals evolved or at most that the pH has changed extremely slowly so that these animals could evolve to live in the changed environment. However, even with the stringent requirement that the pH of sea water should not change by more than one-half unit, the atmospheric carbon dioxide amount can still vary by a factor of fifty and maintain equilibrium between the atmosphere and the oceans. Thus very large changes in the atmospheric carbon dioxide amount can occur without influencing either marine or land animals; still larger variations would even be possible over time intervals sufficiently long to allow the animals to adapt to their new environment. All calculations of radiocarbon dates have been made on the assumption that the amount of atmospheric carbon dioxide has remained constant. If the theory presented here of carbon dioxide variations in the atmosphere is correct, then the reduced carbon dioxide amount at the time of the last glaciation means that all radiocarbon dates for events before the recession of the glaciers are in question. Variations in the concentration or distribution of any gas that absorbs in the infrared portion of the spectrum can influence the surface temperature in the same manner as we have already discussed for carbon dioxide. Ozone and water vapor are the only two other gases that absorb in this region and also exist in the atmosphere in sufficient quantities to have an appreciable effect. Few suggestions have been made that relate variations in the concentration of these two gases to the climate, since these changes do not seem to be related directly to definite geological factors. However, recent calculations have shown that variations in the distribution of ozone can appreciably change the surface temperature. Normally the ozone concentration has a maximum in the stratosphere with relatively small amounts at lower altitudes. Vertical air currents occasionally bring some of the ozone down from the stratosphere, thus greatly increasing the concentration at lower altitudes. This is sufficient to increase the surface temperature from radiation effect by several degrees. The relative humidity as a function of altitude is continually changing and a similar effect on the surface temperature exists for water vapor. These relatively rapid variations in
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temperature are superimposed on those from carbon dioxide alone. The latter variations are relatively constant over long time intervals compared to the former. *** A very large number of different theories of climatic change has been proposed. As more evidence about past climatic change is obtained, each theory has to meet continually more rigorous tests in order to explain the known facts. Each of the major theories of climatic change predicts a different temperature trend during the remainder of this century. A comparison of these predictions with the actual record at the end of the century will provide an important test of these theories. The variable sun theory predicts that the temperature will decrease for some decades. The maximum of the 80-year period in the sunspot cycle probably occurred in 1947. Thus the total energy received from the sun including the ultraviolet should decrease for some decades when the records are averaged over the shorter periods in the cycle. On the other hand a continued increase in the average temperature could be justified by the variable sun theory only if measurement showed a corresponding increase in the solar constant. Changes in the average elevation of the continents clearly cannot be used to explain any variations in the climate over a period of a few centuries. However, the volcanic dust theory predicts appreciably lower temperatures for a few years following volcanic activity that throws large quantities of dust into the atmosphere. The last such explosion was when Katmai on the Aleutian Islands erupted in 1912. More volcanic explosions of this kind must occur before sufficient data can be obtained to correlate with the predictions of this theory. At the present time it is entirely possible that volcanic dust creates small perturbations in the climate while the general trend is determined by some other factor. On the other hand the carbon dioxide theory is the only one that predicts a continually rising average temperature for the remainder of this century because of the accumulation of carbon dioxide in the atmosphere as a result of industrial activity. In fact the temperature rise from this cause may be so large in several centuries that it will present a serious problem to future generations. The removal of vast quantities of carbon dioxide from the atmosphere would be an extremely costly operation. If at the end of this century the average temperature has continued to rise and in addition measurement also shows that the atmospheric carbon dioxide amount has also increased, then it will be firmly established that carbon dioxide is a determining factor in causing climatic change. www.americanscientist.org
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References Arrhenius, S. 1896. On the influence of carbonic acid in the air upon the temperature of the ground. Philosophical Magazine 41:237. Callendar, G. S. 1938. The artificial production of carbon dioxide and its influence on temperature. Quarterly Journal of the Royal Meteorological Society 64:223. Callendar, G. S. 1949. Can carbon dioxide influence climate? Weather 4:310. Chamberlain, T. C. 1897. A group of hypotheses bearing on climatic change. Journal of Geology 5:653. Chamberlain, T. C. 1898. The influence of great epochs of limestone formation upon the constitution of the atmosphere. Journal of Geology 6:609. Chamberlain, T. C. 1899. An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis. Journal of Geology 7:545. Harvey, H. W. 1945. Recent Advances in the Chemistry and Biology of Sea Water. Cambridge: Cambridge University Press. Hulbert, E. O. 1931. Physical Review 38:1876. Kaplan, L. D. 1950. Journal of Chemical Physics 18:186. Kaplan, L. D. 1952. Journal of Meteorology 9:1. Kulp, J. L. 1952. The carbon 14 method of age determination. Scientific Monthly 75:259. Plass, G. N. 1952. Journal of the Optical Society of America 42:677. Plass, G. N. 1952. Journal of Meteorology 9:429. Plass, G. N. 1953. The carbon dioxide theory of climatic change. Bulletin of the American Meteorology Society 34:80. Plass, G. N. 1954. Journal of Meteorology 11:163. Plass, G. N. 1956. The influence of the 9.6 micron ozone band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82:30. Plass, G. N. 1956. The influence of the 15 micron ozone band on the atmospheric infra-red cooling rate. Quarterly Journal of the Royal Meteorological Society 82. Plass, G. N. 1956. Tellus 8. Plass, G. N., and D. I. Fivel. 1953. Astrophysical Journal 117:225. Plass, G. N., and D. I. Fivel. 1955. The influence of variable mixing ratio and temperature on the radiation flux. Quarterly Journal of the Royal Meteorological Society 81:48. Plass, G. N., and D. I. Fivel. 1955. A method for the integration of the radiative-transfer equation. Journal of Meteorology 12:191. Rubey, W. W. 1951. Geologic history of sea water. Geological Society of America, Bulletin 62:1111. Shapley, H., et al. 1953. Climatic Change: Evidence, Causes, and Effects. Cambridge, Mass.: Harvard University Press. Sverdrup, H. U., M. W. Johnson and R. H. Fleming. 1942 The Oceans: Their Physics, Chemistry and General Biology. New York: Prentice Hall. Tyndall, J. 1861. On the absorption and radiation of heat by gases and vapours, and on the physical connection of radiation, adsorption, and conduction. Philosophical Magazine 22:169. Urey, H. C. 1952. The Planets: Their Origin and Development. New Haven, Conn.: Yale University Press. Wiseman, J. D. H. 1954. The determination and significance of past temperature changes in the upper layer of the equatorial Atlantic Ocean. Proceedings of the Royal Society of London A222:296.
For relevant Web links, consult this issue of American Scientist Online: http://www.americanscientist.org/ issues/id.82/past.aspx
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January–February
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What looks like embroidery here is a colored rendering of a complete set of innervating motor axons in a neuromuscular circuit connected to a muscle that moves a mouse’s ear. Multiple renderings revealed variation in the circuit, even in the same animal. Development of such circuits “is just like having the same two teams play more than one football match,” Jeff W. Lichtman says. “They follow the same rules but no two games are alike.”
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Sightings
Real-Deal Connectivity Until recently, images of neural circuits in mammals were based partly on statistical inference that was achieved by sampling some neurons and axons in one circuit. No more. Last winter, Ju Lu, a Harvard University graduate student in Jeff W. Lichtman’s laboratory, published the first complete map of a neuromuscular circuit—a connectome—in a mouse. The full picture revealed unexpected variation in the wiring of a complex nervous system. Lichtman explained its importance to American Scientist associate editor Catherine Clabby. A.S. What prompted this project?
A.S. What technology makes this view possible?
J.W.L. I’m a developmental neurobiologist. My research focuses on ways the nervous system goes from its developmental state to the fully functioning mature state. We think of the human brain as the most sophisticated and competent brain on the planet. We forget that at birth, remarkably, we have the most poorly functioning brain of any animal. A dragonfly with no training probably could chase a mosquito the first time it unfolds its wings. It takes much more time for humans to acquire and adjust to information about the world around us. For example, it takes a year to learn how to walk. Surprisingly, when you look at wiring diagrams of human and other mammalian brains in early postnatal development, their wiring is more complicated than it ends up in adulthood. Apparently, we trim away all but a small subset of neuronal interconnections initially established. Researchers generate these wiring diagrams, also known as connectomes, to understand what kind of rules shape the wiring, how it is that we encode our life experience into the wiring diagram of our brains.
J.W.L. We used genetically modified animals, altered to express fluorescent proteins in their spinal motor neurons. For this study we had to see every single nerve projecting to a muscle. In this case, every cell fluoresced yellow, but the wires intermingled into a tangled mass not unlike a bowl of yellow spaghetti. In order to trace out each one, we had to generate very good optical images. Then we had to very precisely trace each of the little wires. In this case we are talking about a trivially small number of motor neurons supplying this small muscle: just 15 axons reaching about 200 muscle fibers. But getting all the wires traced required tens of thousands of microscopy images and a data set that often approached 100 gigabytes for one muscle. The tracing was computer assisted but it was not fully automated. Ju Lu, who led this work, had to help the computer around the rough spots. It was slow. The first took six months to trace. Now things take a few weeks but it is still tedious work. A.S. Where will this take your research?
A.S. When you saw them, what surprised you? J.W.L. Nerves that move ears on either side of a mouse’s head are not exactly the same. That’s very different from the striking stereotypy that has been observed in animals such as insects. In invertebrates, genetic control over wiring ensures that each animal is optimally wired up in much the same pattern. But the mammalian nervous system seems a bit unfettered from genetic control. The guiding principle might be self-organization based on competitive interactions between nerve cells that begin by sharing the same targets but then vie for them. This group of nerve cells needs to come up with a solution to get a job done, that allows the function to occur (such as wiggling the ears) with no neuron taking on too much and no neuron doing not enough. We can see this process of self-organization unfold in muscles with time-lapse imaging. Initially several different nerves contact each muscle fiber. Due to competition, some branches are pruned while others persist. Self-organization may allow the nerve cells to create a workable solution that, while not necessarily optimized, is good enough. That gives rise to variation. www.americanscientist.org
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J.W.L. I’d like to extend this kind of analysis to other parts of the nervous system during early development. We think doing this fluorescence imaging along with electron microscopy, which has better resolution, offers us a way of seeing every synapse in the brain of an animal of any age. When you start looking at younger animals, there are a lot more wires. They are thinner and packed closer together. Because we have developed means of using multiple colors to make “brainbow” brain images, we are hopeful that circuit tracing will get easier. For example, in developing muscles we can match the one purple axon entering a muscle with all the synapses in that same color without having to trace out every branch point. In young mice, we are beginning to see patterns in the ways nerves interact that we hadn’t seen before. These patterns show the power of tools that allow one to see things that were previously hidden. Many times we see things we didn’t expect— and that is good!
In Sightings, American Scientist publishes examples of innovative scientific imaging from diverse research fields. 2010 January–February
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Scientists’ Bookshelf
The Play’s the Thing Michael Bérubé ON THE ORIGIN OF STORIES: Evolution, Cognition, and Fiction. Brian Boyd. xiv + 540 pp. The Belknap Press of Harvard University Press, 2009. $35.
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et me explain a thing or two about humanists like me. There are legions of us who reach for our guns when we hear the word genome. That’s because we’re all too familiar with the history of eugenics, and we flinch whenever someone attempts an “evolutionary” explanation of Why Society Is the Way It Is; we suspect them, with good reason, of trying to justify some outrageous social injustice on the grounds that it’s only natural. Likewise, there are legions of us who clap our hands over our ears when we hear the term evolutionary psychology. That’s because we’re all too familiar with the follies of sociobiology, and we’ve suffered through lectures claiming that our species is hardwired for middle-aged guys dumping their wives for young secretaries and students (I sat through that lecture myself) or that men run the world because women have wide hips for childbearing, whereas men can rotate three-dimensional shapes in their heads (okay, that one is a mash-up of two different lectures). Brian Boyd is here to change all that. On the Origin of Stories attempts an evolutionary explanation of the appearance of art—and, more specifically, of the utility of fiction. From its title (with its obvious echo of Darwin) to its readings of The Odyssey and Horton Hears a Who!, Boyd’s book argues that the evolution of the brain (itself a development of some significance to the world) has slowly and fitfully managed to produce a species of primate whose members habitually try to entertain and edify one another by making stuff up. If this sounds reductive, don’t worry: Boyd patiently explains that this isn’t your father’s sociobiology or your great-grandfather’s eugenics. To say that something is genetic is not, despite decades of bad science followed by decades of bad popularizations of bad science, to say that it is genetically determined, if “determined” means (as it usually does) “inevitably fated.” Boyd expresses some exasperation at the idea of genetic determinism, arguing that the notion that genes shape us is less deterministic than the notion that we are
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the product of our environment, since the complexity and randomness of genetic recombination in sexual reproduction means that we are each the result of an unpredictably generated variation unique to each of us rather than of anything imposed from without. Thus, writes Boyd, “we should see genes less as constraints than as enablers,” just as “we should see genes not as deniers of the role of the environment but as devices for extracting information from the environment.” Boyd acknowledges that “those uneasy about applying evolution to human behavior often assume that doing so must require stressing selfishness and competition at the expense of altruism and cooperation,” but notes that it ain’t necessarily so: “[Richard] Dawkins points out that he could with equal validity, though with less impact, have called his famous first book not The Selfish Gene but The Cooperative Gene.” Well, that’s nice to know after all these years, now that three decades of popularscience enthusiasts have convinced themselves that Nature herself speaks in the language of Ayn Rand. One hopes the word will get around. Indeed, one of the virtues of On the Origin of Stories is that its author is up to speed on recent work in neurology, genetics and evolutionary theory. He is therefore ideally positioned to persuade his fellow humanists that a “biocultural” approach to art and literature doesn’t entail any Just So stories about how humans came to love Just So stories, or any triumphant tales of how self-replicating molecules persevered over a few billion years until they reached the telos of existence, at which point they were capable of producing Everybody Loves Raymond. For as Darwin insisted, evolution doesn’t have a telos. It consists of a series of open-ended experiments with no final end in sight: “A Darwinian system . . . remains open, unpredictable, and free. It cannot presuppose a best option, an ideal fit, a goal that can be precisely determined beforehand.” Regrettably, Boyd stumbles out of the gate, working himself into a nasty and unnecessary self-contradiction in the first chapter, where he
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argues that “the cultural constructionist’s view of the mind as a blank slate is ‘a dictator’s dream,’ [quoting Steven Pinker],” for “if we were entirely socially constructed, our ‘society’ could mold us into slaves and masters, and there would be no reason to object.” This is a shallow conception of social constructionism (admittedly, a conception often promulgated by social constructionists), in which saying that “X is socially constructed” is tantamount to saying “X can be changed at will.” But what makes Boyd’s critique so unfortunate (and self-contradictory) is that he immediately proceeds to insist that, unlike social constructionism, “an evolutionary view allows for informed social change.” He goes on to note that “Owen Jones compares the law to a lever to change human behavior, and an informed knowledge of human nature to the fulcrum the lever needs to exert its force.” I’m sorry, but I think I might have missed something here. How is this evolutionary view of how to change human behavior not a dictator’s dream? Once we get past that little tangle, however, the first half of On the Origin of Stories is exhilarating. Boyd rehearses the history of the rapid growth in hominin brain size over the past couple of million years, showing that with the development of the neocortex we’ve been endowed with all kinds of cleverness to compensate for the fact that we’re slow, weak, flat-toothed and clawless. We are thoroughly social creatures, and when we work together we can be formidable predators; accordingly, we’ve evolved various attributes that enable mutualism, such as shared attention, mirror neurons and theory of mind. The latter allows us access to something no other animal seems aware of, namely, the notion that other members of our species might have false beliefs. The survival value of art, then, is that it hones and enhances those functions of mind that in turn enhance our capacity for social interaction and exploration: “Art develops in us habits of imaginative exploration, so that we take the world as not closed and given, but open and to be shaped on our own terms.” By refining and strengthening our sociality, by making us readier to use the resources of the imagination, and by raising our confidence in shaping life on our own terms, art fundamentally alters our relation to the world. The survival consequences may be difficult to tabulate, but they are profound. We have long felt that art matters to us. It does, objectively as well as subjectively. By focusing our attention away from the given to a world of shared, humanly created possibility, art makes all the difference. This is rousing stuff. Not only does it reassure us that all our museum-brochure rhetoric is telling the truth, it also confirms that Friedrich Schiller was right to propose, in On the Aesthetic Education of Man (1794), that humans possess a www.americanscientist.org
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WHEN EXPERIMENTS TRAVEL: Clinical Trials and the Global Search for Human Subjects. By Adriana Petryna. • EXPLOITATION AND DEVELOPING COUNTRIES: The Ethics of Clinical Research. Edited by Jennifer S. Hawkins and Ezekiel J. Emanuel. • CHASING MEDICAL MIRACLES: The Promise and Perils of Clinical Trials. By Alex O’Meara. Reviewed by Sheldon Krimsky. Can medical science advance without exploiting vulnerable populations?
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ECOLOGICAL DEVELOPMENTAL BIOLOGY: Integrating Epigenetics, Medicine, and Evolution. By Scott F. Gilbert and David Epel. Reviewed by Marvalee H. Wake. In this fascinating and highly readable introduction to the new field known as eco-devo, Gilbert and Epel show that the environmentally contingent aspects of development have important implications
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THE PRINCETON COMPANION TO MATHEMATICS. Edited by Timothy Gowers and associate editors June Barrow-Green and Imre Leader. Reviewed by Ronald Graham. “If I had to choose just one book to give an interested reader some idea of the scope, goals and achievements of modern mathematics,” writes Graham, “without a doubt this would be the one”
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INCEST AND INFLUENCE: The Private Life of Bourgeois England. By Adam Kuper. Reviewed by Gowan Dawson. Bourgeois families in 19th-century England often used endogamy to keep the money and property they had acquired in the family, says Kuper; the intermarriages between Charles Darwin’s family and the Wedgwood clan are a case in point
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THE NEW FOUNDATIONS OF EVOLUTION: On the Tree of Life. By Jan Sapp. Reviewed by W. Malcolm Byrnes. Sapp shows that microbes have always been problematic for evolutionary biologists and brings to life the debates over how construct a tree of life based on molecular phylogenetics
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NAMING NATURE: The Clash Between Instinct and Science. By Carol Kaesuk Yoon. Reviewed by Kristin Johnson. In this history of biological systematics, Yoon argues that by turning the task of “naming nature” over to scientists, we have become disconnected from the living world; the remedy, she says, is for us to reconnect with the instinctive perspective on the order of nature that we were born with, a carryover from our time as hunter-gatherers
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THE CALCULUS OF FRIENDSHIP: What a Teacher and a Student Learned about Life While Corresponding about Math. By Steven Strogatz. Reviewed by David T. Kung. A shared love of calculus keeps a teacher and student in touch for decades
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LIVING AT MICRO SCALE: The Unexpected Physics of Being Small. By David B. Dusenbery. Reviewed by Thomas R. Powers. Dusenbery does a nice job of explaining the physical constraints under which microorganisms must accomplish such tasks as locomotion and feeding
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THOSE FASCINATING NUMBERS. By Jean-Marie De Koninck. Reviewed by Brian Hayes. What makes a number interesting?
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NANOVIEWS. Short takes on three books: Stories in Stone • Early Spring • Am I Making Myself Clear?
2010 January–February
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Having proposed an evolutionary theory of literature, Horton the Elephant awaits the inevitable monkey trial.—Just kidding, of course. Horton, at lower right, is actually trying to protect the invisible residents of Who-ville from the kangaroos and the Wickersham clan, who are threatening to boil the Whos in Beezle-Nut oil. This two-page excerpt from Dr. Seuss’s Horton Hears a Who! is reproduced in On the Origin of Stories and discussed in detail by Brian Boyd.
“play-drive” that leads us to create and be amazed by art: For, to declare it once and for all, Man plays only when he is in the full sense of the word a man, and he is only wholly Man when he is playing. This proposition . . . will, I promise you, support the whole fabric of aesthetic art, and the still more difficult art of living. It is no slight to Boyd, surely, to say that On the Origin of Stories sometimes reads like Schiller combined with a few graduate courses in neuroscience. Whether one prefers to say, with Emily Dickinson, “If I feel physically as if the top of my head were taken off, I know that is poetry,” or, with Boyd, “Neurons in the substantia nigra and the ventral tegmental areas of the brain secrete dopamine in reaction to the surprising but not to the expected,” is surely a matter of taste. The second half of the book, however, probably won’t go over as well with the humanists Boyd is trying to reach. He opens that half by assuring us that “a biocultural approach to literature simply requires that we take seriously that evolution has powerfully shaped not just our bodies but also our minds and behavior.” This much is incontrovertible, and I share Boyd’s hope that someday our fellow humanists will 72
be less averse to thinking in terms of the species-wide universals we’ve inherited as part of the legacy of life on Earth. But Boyd’s application of the principle seems to me to have two weaknesses. The first, upon which some reviewers have already remarked, is that the resulting readings of The Odyssey and Horton Hears a Who! don’t appear to be entirely worth the journey. Much of Boyd’s approach consists of explaining how Homer and Dr. Seuss manage to win and keep our attention, and Boyd castigates contemporary literary criticism for failing to attend to this important matter. But might it not be that “Homer organized the poem in this way so as to win and keep your attention” is the kind of thing that, in literary criticism, literally goes without saying? Similarly, readers for almost three millennia have recognized that Odysseus is one crafty fellow, and that one indication of his craftiness is that he does not act on impulse; even when he’s trapped in a cave with a one-eyed giant eating his men, he takes a deep breath and comes up with a well-considered plan. Boyd explains precisely what this means in neurological terms: “Rapid-fire reactions have to be inhibited (in the orbitofrontal cortex) so that there is time to formulate and assess new options (in the dorsolateral cortex) before acting on them.” Personally, I am tremendously pleased that
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my species has gotten to the point at which it understands things like this. But how much is added to the history of criticism, finally, by the realization that Odysseus was doing his crafty plotting in his dorsolateral cortex? I mean this as a real and not a rhetorical question. Boyd closes On the Origin of Stories by remarking that “evocriticism” will have to make its way by devising compelling and convincing readings of works of literature, attending not only to the universal features of human minds but also to the cultural and historical particularities of time and place. On one hand, this school of criticism will provide a desperately needed justification for literary study: “If storytelling sharpens our social cognition, prompts us to reconsider human experience, and spurs our creativity in the way that comes most naturally to us”—as it surely does—“then literary studies need not apologize.” On the other hand, evocriticism comes bearing not only a rationale but also a sword: As Boyd remarks time and again, the enemy to be vanquished is Theory, which cuts literature off from life by emphasizing human thought and ideas as the product of only language, convention, and ideology—although Theory then tries to compensate for severing literature from three-dimensional life by insisting that it is always political or ideological. Well, Theory-bashing can be good fun, I suppose, and some forms of theory deserve it. But it is odd to suggest that stressing “language, convention, and ideology” somehow cuts one off from “life.” And it’s even odder to note that “a fine work of art not only expresses creativity but also inspires it in those who enjoy it” but fail to consider that “theoretical” readings of language and literature caught on in the 1970s and 1980s because they were, back in the day, compelling and creative. Everyone who, like Boyd, believes that Alan Sokal killed theory dead really should go back and read Barbara Johnson on Melville’s “Billy Budd” or Paul de Man on the famous rhetorical (or is it real?) question that closes Yeats’s “Among School Children.” Even though I’ve never been a card-carrying deconstructionist myself, I was fascinated by those readings because they taught me that Melville’s novella was even more extraordinary than I’d thought, and that when you’re
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trying to determine whether a question is real or rhetorical, even an utterance like “Eh, what’s the difference?” can open onto a hall of mirrors. Boyd never stops to consider that maybe, just maybe, the clever human minds responsible for literature are the same clever human minds responsible for literary theory; if he had, he might have been able to say, more plausibly, that theory started (as do all our endeavors) in the impulse to play and create, and only became routine and stultifying after many weary iterations. At which point, after the 350th New Historicist reading of The Tempest, neurons in the substantia nigra and ventral tegmental areas of the brain stopped secreting dopamine. More important, Boyd is sometimes reluctant to give culture and history their due. He scoffs, for example, at the idea that romantic love was invented at some point in the 12th century, because
“cross-cultural, neurological, and crossspecies studies have demonstrated the workings of romantic love across societies and even species.” This just won’t wash. Other species might court and mate for life, but they do not engage in romantic love in the sense that humanists employ the term, save perhaps for the cartoon skunk Pepé Le Pew. “Romantic love” does not mean “mammals doing it like mammals”; it refers to the conventions of courtly love, which were indeed invented in the European middle ages and cannot be found in ancient literatures or cultures. Those conventions are culturally and historically specific variations on our underlying (and polymorphous) biological imperatives, just as the institution of the Bridezilla and the $25,000 wedding is specific to our own addled time and place. Nothing about the evolutionary record, from amoebas to Homo sapiens
CLINICAL RESEARCH
Help, Harm and Human Subjects Sheldon Krimsky WHEN EXPERIMENTS TRAVEL: Clinical Trials and the Global Search for Human Subjects. Adriana Petryna. xii + 258 pp. Princeton University Press, 2009. $65 cloth, $24.95 paper. EXPLOITATION AND DEVELOPING COUNTRIES: The Ethics of Clinical Research. Edited by Jennifer S. Hawkins and Ezekiel J. Emanuel. viii + 327 pp. Princeton University Press, 2008. $65 cloth, $24.95 paper. CHASING MEDICAL MIRACLES: The Promise and Perils of Clinical Trials. Alex O’Meara. viii + 263 pp. Walker and Company, 2009. $25.
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hose of you who browse bulletin boards or ride in buses or subway cars have undoubtedly come across posters bearing messages like this: “If you are between the ages of 18 and 35 and have difficulty sleeping, you may qualify to participate in a new study that could help your condition.” Such solicitations are now nearly ubiquitous. That’s because the clinical trial business has grown significantly over the past several decades, largely in response to the growth of drug development and of global markets in pharmaceuticals. To get new drugs into the marketplace, companies must deliver safety and efficacy data from clinical trials to the U.S. Food and Drug Administration (FDA). It is estimated that every year about 2.3 million people take part in clinical trials held in the United States; in 2008, www.americanscientist.org
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more than 65,000 such trials, sponsored by federal agencies and private industry, were listed in a National Institutes of Health (NIH) database for those trying to locate clinical trials. Investment in drug development has grown steadily since the 1980s as a result of biomedical advances relating to stem cell research, pharmacogenetics, proteomics and the mapping of the human genome. Recently the drug industry has been spending the money it budgets for research and development on a new generation of cancer drugs. As Big Pharma has investigated these oncologic agents, more volunteers have been needed in clinical trials to evaluate the prospects of various compounds. Many trials have had difficulty recruiting subjects. According to a 2006 article by Judith M. Watson and David J.
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sapiens, is denied or contravened in acknowledging this. On the Origin of Stories is a fascinating book, even a necessary book. At its best, evocriticism can help to reorient the arts and humanities, renewing (or, in some benighted quarters, sparking) our appreciation for the creative works of human minds and hands, and leading humanists to take a fresh look at the rich evolutionary record. But it will accomplish this, I suspect, only if it is complementary to, and not sweepingly dismissive of, the intellectual traditions humans have devised for the study of human cultures. Michael Bérubé is the Paterno Family Professor in English Literature and Science, Technology, and Society at Penn State University. He is the author of, among other books, Rhetorical Occasions: Humans and the Humanities (University of North Carolina Press, 2006) and The Left at War (New York University Press, 2009).
Torgerson, “Increasing Recruitment to Randomized Trials” (BMC Medical Research Methodology 6:34), a survey of the corresponding authors of articles published in 2000 or 2001 reporting the results of randomized trials revealed that nearly 60 percent of the trials had either proceeded with fewer subjects than initially planned or found it necessary to extend the recruitment period. And more recently Sarah Kliff, in an article published online in Newsweek on March 10, 2009, has reported that 80 percent of clinical trials are delayed at least a month because of low enrollment. When people cannot be recruited for trials in the United States, the world marketplace becomes the stage for medical outsourcing. Eastern Europe, Africa, Asia and South America have helped fill the demand for human trial subjects, usually with indigent people who have little or no access to health care. According to a report from Visiongain (a company that provides business information to the pharmaceutical industry), in 2008 the global clinical trial business was worth about $50 billion and was growing at a rate of 10 percent a year. Three recently published books address the subject of clinical trials from different vantage points. When Experiments Travel, by Adriana Petryna, is an ethnographic analysis of leaders in the new growth industry of Contract Research Organizations (CROs), which provide clinical-trial services to drug developers. Exploitation and Developing 2010 January–February
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Countries, edited by Jennifer S. Hawkins and Ezekiel J. Emanuel, is a volume of essays by bioethicists focusing on issues of global equity and justice in clinical trials that enroll impoverished groups in developing nations. And Chasing Medical Miracles is journalist Alex O’Meara’s memoir of his experiences jumping through hoops to gain access to a clinical trial that gave hope of a cure for his diabetes. In When Experiments Travel, Petryna, an anthropologist at the University of Pennsylvania, explores this question: Why are so many of the clinical trials sponsored by companies in the United States being held in developing nations? To explain the phenomenon known as “offshoring of trials,” Petryna analyzes information gleaned from government sources, the Web sites of nonprofit organizations, and interviews with leading scientists and entrepreneurs who have founded CROs. She learns that, as is true of many trends in globalization, government policies play a central role. “In the early 1990s,” she notes, “the FDA began to actively promote the globalization of clinical trials, declaring that the search for sites and sources of data is part of its mandate.” After examining the global marketplace for human subjects, Petryna concludes that the norms of protection vary significantly among countries. The book is built primarily on her scholarly, detached presentation of qualitative interview data and an analysis of published statistics. However, she periodically expresses moral judgments such as the following: “The benefits deriving from globalized research are arguably uncertain, and its risks are unevenly distributed and its costs, unjust.” Petryna condemns First World companies and complicit governments for exploiting vulnerable, impoverished patients as experimental subjects. However, many of the complex ethical issues of transnational human trials are left unexplored in her book. Among those are whether desperate people can be both exploited and helped, and what set of humane principles should guide outsourced clinical trials. These are the subjects of the volume edited by Hawkins and Emanuel, Exploitation and Developing Countries. The essays in this collection are organized primarily around two cases, which serve as the grist for ethical analysis. In the Havrix case, 40,000 school children in Thailand received either an inacti74
vated hepatitis A vaccine or a hepatitis B vaccine in a randomized controlled trial sponsored by the U.S. Army in conjunction with SmithKline Beecham Biologicals and Thailand’s Ministry of Public Health. In the Surfaxin case, 650 premature infants in Bolivia who had respiratory distress syndrome (RDS), for which the standard treatment was lung surfactant replacement therapy with one of four approved surfactant drugs, were subjects in a placebo-controlled trial of a new surfactant made by Discovery Labs. In addition, in the introduction to Exploitation and Developing Countries, there is a discussion of trials in sub-Saharan Africa in which women were treated with antiviral agents to reduce maternal-fetal transmission of HIV.
Is it ethical to use placebo controls against a new drug in clinical trials when some form of effective therapy exists for a medical condition and is the standard of care? The essayists reflect on a series of moral dilemmas. Can there be informed voluntary consent when the clinical trials are conducted in countries in which people face extreme poverty, illness and desperation? Is it ethical to use placebo controls against a new drug in clinical trials when some form of effective therapy exists for a medical condition and is the standard of care? When is a clinical trial protocol exploitative of desperate human subjects? Should U.S. companies engaged in overseas trials be required to follow ethical and medical standards that are no less stringent than those they would be required to follow in the United States? Or should the moral acceptability of a trial be based on whether the company’s actions will improve the lives of the population of the country where the trial will be conducted? A number of the essays address the complex issue of placebos. Thomas Pogge (“Testing Our Drugs on the Poor Abroad”) explores the question of whether it is “wrong to test a new medi-
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cine (Surfaxin) for some life-threatening medical condition (RDS) with a placebocontrol design when there already exists an effective medicine for this condition against which the new drug could be tested.” Pogge points out that if the Surfaxin trial had had an active control design, the lives of more than 280 infants might have been saved; nevertheless, with the placebo-control design, the trial saved the lives of 140 infants who probably would have died if the trial had not been conducted in Bolivia. The book’s contributors examine responses to ethical questions through the lens of a variety of ethical theories: utilitarianism (greatest good for the greatest number), deontology (respect for persons), virtue ethics (accepted standards and norms), Rawlsian justice (the most vulnerable must not be made worse off), situation ethics (contextualized to local conditions) and intuitionism (what feels fundamentally fair and just). The meaning of exploitation in the circumstances discussed remains elusive; nevertheless, the volume’s artful philosophical analyses illuminate the issues. Andrew Siegel, in “Kantian Ethics, Exploitation and Multinational Clinical Trials,” expresses the paradoxical dialectic: We must also exercise caution when legislating against exploitation, for the perverse reality is that the best prospect some persons currently have for improving their lives is to submit to exploitative exchanges. In “Exploitation and Placebo Controls,” Jennifer Hawkins proffers a set of conditions that she believes are jointly sufficient to morally justify the use of placebo controls even when participants fail to receive the best care available. The last chapter consists of a consensus statement obtained from participants at an international conference on research in developing countries. It addresses the question of whether it is unethical to recruit persons in a poor country to be clinical-trial subjects when neither they nor their country will benefit from the medical advance being investigated. Overall, these are essays of high quality. However, the anthology is limited in one obvious respect: It has no contributions (with the exception of the consensus statement) from ethicists in those parts of the world most adversely affected by clinical-trial outsourcing.
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The two books already discussed, which are soberly academic in tone, were written by scholars pursuing broad explanatory themes and universal ethical principles. Alex O’Meara’s Chasing Medical Miracles, the first-person account of a clinical-trial subject, is almost breezy in comparison—the book is a page-turner. O’Meara, a journalist, has type I diabetes complicated by hypoglycemic unawareness that has repeatedly landed him in emergency rooms. He describes the lengths to which he goes to be included in a somatic gene therapy trial that would afford him some hope that his body would begin producing its own insulin. What makes his memoir unique and captivating is that he steeped himself in the culture of clinical trials, entering not as a naive and illinformed subject but as a fully informed and tenacious advocate of the trial, which he hoped would liberate him from having to wear an insulin pump. His personal story is so compelling that the intervening background chapters feel like an unwelcome intrusion. The trial involved transplanting pancreatic islet cells from matched do-
nors into the livers of patients with diabetes. To be cleared for participation, O’Meara had to overcome a number of obstacles. To take just one example, an x-ray of his lung revealed a nodule. He volunteered to undergo surgical removal of the nodule, hoping that it would turn out to be fungal, since in that case he would still be eligible for the trial. The surgeon needed 98 titanium staples to close his lung after the surgery. “I saw the little rivets on my x-ray,” O’Meara writes. “They were looking great, the surgeon said. And no, he told me, the staples wouldn’t set off metal detectors at airports.” If the book has a weakness, it is that the author makes it appear that, to qualify for a trial, a candidate must be in tip-top physical shape (O’Meara was a marathon runner). His case is hardly representative of the way people actually get recruited for trials or of the type of medical screening that usually takes place to ensure that the trial candidate meets the letter of the protocol. O’Meara’s trial was fraught with risks, and things did not go smoothly for him: He experienced multiple complications and got mixed results. Thus
BIOLOGY
Development in the Real World Marvalee H. Wake ECOLOGICAL DEVELOPMENTAL BIOLOGY: Integrating Epigenetics, Medicine, and Evolution. Scott F. Gilbert and David Epel. xvi + 480 pp. Sinauer Associates, Inc., 2009. $49.95 paper.
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hat constitutes a new field in science? Must it be the consequence of a new synthesis? Does it need to take research in a new direction based on new ideas or new techniques? Or is it something that we recognize after the fact as a paradigm change? If we take these to be the criteria, then ecological developmental biology certainly qualifies as a new field, for it fulfills them all. Anyone wanting to learn more about “eco devo” would do well to read Scott F. Gilbert and David Epel’s recent magnum opus, Ecological Developmental Biology: Integrating Epigenetics, Medicine, and Evolution. The same applies for those who may have been wondering what the currently emphasized “new biology” is all about. The new paradigm for
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biology in the 21st century is integration—of the various subfields of biology, and of biology with other fields, including physics, chemistry, geology, the social sciences and the humanities—and the goal is to understand the complexity of living systems and their dynamic nature. Several scientists interested in integration have been writing discourses on why it is important and how it can be facilitated. But Gilbert and Epel have chosen to leapfrog that discursive step to produce a compelling portrait of the new biology in action. The authors have two goals for the book: to offer a “fresh and challenging way of looking at biology,” so that a different set of questions can be asked, and to show how ecological developmental biology is needed to diagnose and po-
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his experience left him well qualified to write the book’s useful afterword, in which he presents a set of soulsearching questions that anyone who is considering enrolling in a clinical trial would do well to consider. Chasing Medical Miracles provides a useful counterpoint to the detached, scholarly approach of social scientists and ethicists featured in the other two books. It reminds us that people in desperation over their illnesses seek hope, and that many of them grasp that hope in a clinical trial that offers them an experimental treatment. Taken together, these three books reveal the profound complexity of the task of meeting the needs of vulnerable populations while advancing medical science for the benefit of future generations. Sheldon Krimsky is a professor in the Department of Urban and Environmental Policy and Planning at Tufts University and an adjunct professor in the Department of Public Health and Community Medicine at Tufts University School of Medicine. He is the author of, among other books, Science in the Private Interest (Rowman and Littlefield, 2004) and is coauthor with Tania Simoncelli of Genetic Justice (forthcoming from Columbia University Press).
tentially help cure many of the problems of our planet. They emphasize four “revolutions” that are currently under way in biology: Inheritance has been shown to involve the transmission of gene expression patterns as well as gene nucleotide sequences; developmental and ecological explanations for human diseases are being found; phenotypic plasticity is being recognized as a “driving force” in the development and organization of biodiversity; and there is a new focus on analyzing relationships within networks of interaction. The book demonstrates that ecological developmental biology is significant in all four of these trends. Gilbert and Epel hope that by showing how to use the many facets of development to integrate disparate disciplines, the book will stimulate new research. Of course, development in nature can differ in important ways from development in a controlled laboratory environment. Research on development in Drosophila and in mouse models, despite having been enormously productive, has not lent itself to a synthetic approach, because it takes place in laboratories, where the environment is considered constant and consequently unimportant. 2010 January–February
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The environment can have profound effects on an animal’s phenotype. In the presence of cues from the larvae of a predator, tadpoles of the tree frog Hyla chrysoscelis develop strong trunk muscles and a red “warning” coloration (A, left). When Nemoria arizonaria caterpillars hatch in the spring, they eat young oak leaves and develop a cuticle that resembles the oak’s catkins (B, left), but those that hatch in the summer after the catkins are gone eat mature oak leaves and develop a cuticle that resembles young twigs (B, right). The blue-headed male wrasse Thalassoma bifasciatum is more colorful than the females in his cohort (C); if he dies, one of those females will grow testes and change phenotype completely, becoming a male. From Ecological Developmental Biology.
Integrating reductionistic laboratory research with experimental and observational research done in the field can be enlightening, and the book supplies a wealth of examples showing that many scientists have been doing just that. The volume’s intended audience includes undergraduates (the authors maintain that a good first-year biology course should be adequate background) and graduate students as well as professional scientists—particularly biologists, who will want to know how their own areas of interest may be affected by the new biology. Gilbert and Epel, who are 76
distinguished teachers, explain things clearly, supporting (and richly illustrating) their points with many photos, drawings, graphs and sidebars. These draw on the literature about a wide variety of diverse species, so that general principles emerge as the reader sees how ecology guides development in plants and invertebrates as well as vertebrates. Every chapter ends with a useful summary and valuable references. The book is organized so that the flow of information builds the case for ecological developmental biology as a field of study. Part 1 deals with the ways
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that animals integrate signals from the environment into their normal developmental paths. The first chapter gives numerous examples of environmental factors (such as temperature, diet, crowding or the presence of predators) that elicit a particular phenotype. In many species of turtles and crocodiles, for example, the temperature at which an embryo develops determines whether it becomes male or female. Chapter 2 examines the mechanisms by which environmental cues bring about such changes on a molecular level; changes in gene expression brought about by DNA methylation, transcription-factor activation and neuroendocrine regulation are described. Chapter 3 is about developmental symbiosis, particularly between animals and the microbes they host. Bacteria of the genus Wolbachia, for example, are important to the sexual development of many arthropods. And in mammals certain gut bacteria are necessary for the formation of capillary networks in the small intestine. Chapter 4 describes the defenses that embryos have at their disposal to ensure their survival and normal development; many of these operate at a cellular level and include ABC transporter proteins, thiolcontaining compounds, and enzymes. Part 2 deals with the ways in which development can be altered to produce abnormal phenotypes, including what we call disease. Chapter 5, on teratogenesis, looks at environmental agents that disrupt development, such as industrial mercury, ethanol, retinoic acid, cigarette smoke, alkaloids and ionizing radiation. Endocrine disruptors, covered in chapter 6, are also teratogens, but they affect physiological function as well as anatomy. DDT, diethylstilbestrol (DES), soy estrogens, atrazine, bisphenol A (BPA) and polychlorinated biphenyls (PCBs) are all discussed, along with regulatory and policy decisions concerning them. Chapter 7 discusses many instances of adult diseases that result from altered gene expression, usually brought about by inappropriate methylation of DNA. (Methylation can stop a gene from functioning, just as mutation can.) For example, methylation of tumor-suppressor genes and demethylation of oncogenes may be the culprits in tumor cell formation. Part 3 opens with a chapter on the history of evolutionary theory from classical Darwinism to the Modern Synthesis. Gilbert and Epel note that the Modern Synthesis demonstrated four
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things: that evolution within a species can be modeled mathematically; that genes under selection are the units whose frequencies change under Darwinian selection; that organisms with genes allowing them to become fit will produce offspring that are more fit; and that these offspring have a high likelihood of inheriting the genes that made their parents fit. The last two chapters bring development and developmental plasticity into a new synthesis, which applies to evolution both within and above the species level and emphasizes types of genes and variation in gene expression throughout life. Chapter 9, on evolution through developmental regulatory genes, discusses the origins of evo-devo (evolutionary developmental biology), “toolkit genes,” developmental modularity, and developmental genetic sources of variation (including changes in the place or time of gene expression or in the amount of protein produced, as well as changes in the properties of the protein synthesized). In chapter 10 the authors note that the Modern Synthesis, which is more than 50 years old, is in need of a major overhaul, particularly because ecological developmental biology has called into question some of its important assumptions. For example, evolutionarily significant variation is not always the product of genetic variation in alleles, as the Modern Synthesis would have it; some of it is instead the result of epigenetic variation, as when altered chromatin configurations act like alleles. Epigenesis—the production of phenotypes through environmental mediation of gene expression patterns—is a theme throughout the book. Ecological Developmental Biology is filled with concrete examples that illuminate the basic science of topics ranging from interactive gene networks and biochemical pathways to interactions in ecological communities. The authors deftly summarize scientific findings that exemplify the points they want to make. The “cases” discussed usually deal with several levels of the hierarchy of biological organization, integrating molecular, organismal and ecological parameters in a fashion that enhances our understanding of development and evolution. Some cases show the ways in which “normalcy” is maintained or disrupted, and the authors discuss the developmental, ecological and medical implications of the disruptions. The sort of integration I’m referring to occurs on many levels and across chapwww.americanscientist.org
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The DNA methylation patterns of a pair of monozygotic twins are nearly indistinguishable when the twins are young but diverge as they grow older. One technique for revealing methylation differences and similarities involves marking the DNA from one twin with a red dye and that from the other twin with a green dye. Then the nonmethylated DNA is collected and bound to metaphase chromosomes. If red or green bands result, the DNA from one twin has bound, but the DNA from the other has not. In yellow regions, the red and green DNAs have bound equally. It’s also the case that methylation patterns in a single individual change as that person ages. It seems likely that methylation differences will turn out to be important in explaining phenotype divergence and differences in susceptibility to diseases. From Ecological Developmental Biology.
ters. In chapter two, Gilbert and Epel examine transgenerational polyphenism in locusts; transgenerational predatorinduced polyphenisms in radishes, Daphnia (a water flea), aphids and birds; and transgenerational polyphenisms induced by DNA-methylation differences in the toadflax plant and in mice and rats, showing the mechanisms by which polyphenisms can be transmitted across generations. In chapter 6, the authors discuss the transgenerational effects of endocrine disruptors in humans and frogs, and in chapter 7 they consider epigenetic methylation, disease and aging in humans. We learn about gene methylation and the fetal phenotype, cancer as caused by epigenetic methylation, the reciprocity of epigenetic and genetic causation in cancer, the effects of environmental pollutants (most of them introduced by humans) on the molecular biology of genes and development, and the ways such pollutants disrupt normal development in plants, frogs and humans. Information about how development is affected by the health of the environment is interwoven throughout. And as we learn all
this, we acquire new ways of thinking about pattern and process in evolution. The book’s coda, “Philosophical Concerns Raised by Ecological Developmental Biology,” deserves to be widely read. In it the authors discuss many important implications of the integrated developmental perspective presented in the book, observing that it “abolishes any notion of a genetic determinism.” They note that because developmental symbioses are not exceptional cases but the norm, developing organisms can be said to be involved in “co-construction on a massive scale.” Consequently, they recommend taking a broader view of evolution, one that acknowledges interdependence, harmony and integration in nature and includes a cooperative model of evolution alongside the competitive model. Pedagogically, they call for an expansion of disciplinary boundaries and revision of the metaphors used to describe evolution. “Storytelling matters,” they conclude. Evolutionary narratives are the most critical stories in biology, in science, 2010 January–February
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and perhaps in Western civilization, so we had better get them in line with the biological data. In the final paragraph of the coda, reminding the reader that “the rules of the evolutionary process include the crucial notion of ‘becoming with,’” Gilbert and Epel emphasize that “co-development is normative, and evolution is not merely the battle of each against all.” They have demonstrated that an integrative approach that encompasses interactions at all levels (from molecules to ecosystems) is essential. Four succinct but deliciously rich and provocative essays serve as appendices. The first and third offer historical per-
spectives and analyze the contributions of some major figures (Trofim Lysenko, Paul Kammerer, Richard Goldschmidt, C. H. Waddington); the second and fourth clarify epigenetic effects. Gilbert and Epel have produced a book that is enormously thoughtful on a number of levels. I marvel at their capacity to integrate so much information and so many ideas lucidly, succinctly and engagingly. Part of their intention is to develop a new emphasis on integration across the hierarchy of biological organization, and the excellent and diverse examples of integration that they present show how promising the approach is. I expect that their focus on examining the ways that development at all levels re-
M AT H E M AT I C S
A Panoramic View Ronald Graham THE PRINCETON COMPANION TO MATHEMATICS. Edited by Timothy Gowers and associate editors June Barrow-Green and Imre Leader. xxii + 1,034 pp. Princeton University Press, 2008. $99.
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his impressive book represents an extremely ambitious and, I might add, highly successful attempt by Timothy Gowers and his coeditors, June Barrow-Green and Imre Leader, to give a current account of the subject of mathematics. It has something for nearly everyone, from beginning students of mathematics who would like to get some
Monochromatic paths through a lattice of randomly colored hexagons illustrate the concept of percolation in an essay by Gordon Slade included in The Princeton Companion to Mathematics. Both all-gray and all-white paths extend from north to south, but on the east-west axis no monochromatic path crosses the heavy black line. Slade describes notable recent progress in understanding such random processes. 78
sense of what the subject is all about, all the way to professional mathematicians who would like to get a better idea of what their colleagues are doing. The 75-page introduction, which was written by Gowers, gives a very readable account of the basic branches of mathematics (algebra, geometry, analysis) and how these overlap and relate to one another, how they have developed and are continuing to do so, and how they are driven in large part by the types of questions mathematicians ask. This section should be mandatory reading for any prospective mathematics student. Most of the articles that make up the rest of the book were written by leading experts. For example, Carl Pomerance has contributed a stimulating essay on computational number theory, Cliff Taubes provides a wonderful overview of differential topology, and Jordan Ellenberg gives a thoughtful summary of arithmetic geometry. In a few cases, the choice of contributor was more creative. In the preface, the editors say that expository skill was as important a criterion as expertise in the selection of contributors. Even so, they found it necessary to take what they refer to as an “interventionist” approach, editing most of the articles substantially and in some
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sponds to and shapes environments will prove increasingly fertile as it matures, yielding new insights, new approaches, new techniques and new theory. I urge biologists who relish the challenge of new ideas to read this book with care, to use it in courses and seminars, and to discuss with colleagues how to collectively participate in the new biology. Gilbert and Epel have given us a magnificent road map to the healthy future of biology and of life. Marvalee H. Wake is Professor of the Graduate School in the Department of Integrative Biology at the University of California, Berkeley. Her research interests include evolutionary morphology, development and reproductive biology in vertebrates.
cases asking the contributor for a complete rewrite. A great deal of tact must have been required, but the result is that the book is highly readable throughout. Martin Gardner, the most successful recreational mathematics expositor in history, has said that he operates under the principle that if something isn’t completely clear to him, it would be a disservice to his readers to include it, and apparently in that same spirit Gowers and his colleagues decided not to allow any material in the book that they didn’t themselves understand. The level of difficulty is not uniform; they accepted that some of the articles will be too hard for some readers, but their goal was for ideas to be discussed at the most accessible level practical. The introduction is followed by a collection of informative articles on the origins of modern mathematics. Topics covered include number systems, geometry, abstract algebra, algorithms, the development of rigor in mathematical analysis, and the development of the idea of proof. The section concludes with a discussion of the crisis in the foundations of mathematics that occurred during the early part of the 20th century and resulted in the formulation of axiomatic set principles, the rise of intuitionism and the emergence of modern mathematical logic as a refinement of axiomatics. Next is a section consisting of 99 shorter essays on major concepts in modern mathematics, such as the axiom of choice, categories, curvature, the Fourier transform, homology and cohomology, L-functions, manifolds, von Neumann algebras and much more. Some of the essay titles may sound a bit mysterious to nonmathematicians, but the articles
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themselves are almost without exception very accessible and informative. In the section that follows—the longest in the book—the major branches of mathematics are treated in more depth, in 26 articles, each 10 to 30 pages long. These essays vary in style, but they have been made as reader-friendly as possible given the topics covered, which include algebraic geometry, differential topology, moduli spaces, operator algebras and set theory. I particularly enjoyed the piece by Barry Mazur on algebraic numbers and Sergiu Klainerman’s discussion of partial differential equations. These articles help flesh out the basic content of the major subdisciplines of modern mathematics and show how they interrelate. It is interesting to note that one of the longest articles is on computational complexity, a topic that didn’t even exist 50 years ago. It is hard to imagine a mathematician who wouldn’t benefit from reading at least some of these essays. The next section contains pieces one to three pages long on a (somewhat subjective) selection of various major theorems and open problems, such as the ABC conjecture, the Banach-Tarski paradox, Gödel’s theorem, the Riemann hypothesis, the Poincaré conjecture, the P
versus NP problem, Fermat’s Last Theorem and the Weil conjectures. These essays are a very good source of information about the history and current status of many of the classic problems. Given their nature, that status is dynamic, or so we hope at least; as the great German mathematician David Hilbert asserted, “Wir müssen wissen. Wir werden wissen.” (We must know. We will know.) As an example of major progress, we have the recent resolution of the famous Poincaré conjecture. It’s actually discussed in greater detail in the preceding section—in the essay on differential topology, which is cross-referenced here. Next come very brief biographical sketches of 96 famous mathematicians, from Pythagoras to Bourbaki, almost all of them known for work carried out before 1950. After that is a section containing longer articles about the influence of mathematics on such fields as chemistry, biology, cryptography, network design, economics, statistics, music and art. In the final section, “Perspectives,” we find an intriguing assortment of short essays on such topics as the art of problem solving (a subject that continues to elicit strong opinions), mathematics as an experimental science (certainly an
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ever-increasing trend nowadays) and advice for young people who might want to become mathematicians. Overall, Gowers, Barrow-Green and Leader must be congratulated on a magnificent achievement. Of course, even in a book this massive (there are more than 1,000 pages), it’s inevitable that some important topics have been omitted—transcendence theory, for example. No doubt many of these omissions will be rectified in the next edition. It would be nice if the book were available in a lighter-weight multivolume paperback or electronic version; the cloth Companion took up far too much space in my suitcase! If I had to choose just one book in the world to give an interested reader some idea of the scope, goals and achievements of modern mathematics, without a doubt this would be the one. So try it. I guarantee you’ll like it! Ronald Graham is Irwin and Joan Jacobs Professor in the Department of Mathematics and the Department of Computer Science and Engineering at the University of California, San Diego, and chief scientist at the California Institute for Telecommunications and Information Technology. His interests include scheduling theory, computational geometry, Ramsey theory and quasi-randomness.
The MIT Press Human Footprints on the Global Environment THREATS TO SUSTAINABILITY edited by Eugene A. Rosa, Andreas Diekmann, Thomas Dietz, and Carlo C. Jaeger “This book is a major addition to the social science literature dealing with the phenomenon of global environmental change. The editors are to be commended for blazing this trail with elegant conceptualization and style and for an impassioned argument on a critical issue of our times.” — Edward Miles, University of Washington, coeditor of Environmental Regime Effectiveness 328 pp., 1 illus., $27 paper
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Johann Wolfgang von Goethe Introduction and Photographs by Gordon L. Miller “Goethe would be delighted with this edition of The Metamorphosis of Plants. It does what he hoped would eventually become possible and provides pictures situated in the text of all the plants to which he refers, so that we can see for ourselves the specific points to which he is drawing our attention.” — Henri Bortoft, author of The Wholeness of Nature and Goethe’s Scientific Consciousness
FROM INSECTS TO JUMBO JETS, REVISED AND EXPANDED EDITION Henk Tennekes “This was a great little book when it came out in its original edition; this new version is even better, as it contains both Henk’s homage to his favorite flying machine (Boeing 747) and explanations based on some of the unexpected results of recent experiments with bird flight. Read it, then watch the birds and planes, and then dip into it again and again.” — Vaclav Smil, University of Manitoba, and author of Global Catastrophes and Trends
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ARTIFICIAL INTELLIGENCE AND THE HUMAN MIND Diego Rasskin-Gutman translated by Deborah Klosky “This book, in an accessible but profound way, approaches difficult but essential questions about the function of two types of intelligence destined to coexist as parent and child: human intelligence and artificial intelligence.” — Miguel Illescas Córdoba, International Chess Grand Master, Director, Chess Education and Technology, Spain QQ JMMVT DMPUI
To order call 800-405-1619thttp://mitpress.mit.edu tVisit our e-books store: http://mitpress-ebooks.mit.edu
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HISTORY
All in the Family Gowan Dawson INCEST AND INFLUENCE: The Private Life of Bourgeois England. Adam Kuper. viii + 296 pp. Harvard University Press, 2009. $27.95.
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n 1871, a short skit in the humor magazine Punch titled “Most Natural Selection” proclaimed that “If Mr. Darwin’s theory of the Descent of Man were true, we should . . . have to accept quite new views of marriage.” Insisting that it was preferable that married couples should not be near relations, such as cousins, the skit claimed that “if we are descended from Anthropoid Apes . . . we should conclude that there was no cause or just impediment whatever why we should not marry cousins so very many more degrees removed than any other as those arboreal and quadrumanous ones.” Punch’s characteristically facetious contribution to the famous debates over evolution in Victorian Britain undoubtedly shocked many readers with its grotesque and disquieting insinuations regarding conjugal relations between humans and simians. But Charles Darwin himself,
who had pronounced himself reconciled to man’s bestial ancestry in his earliest notebooks, would more likely have been discomfited by what the skit suggested about cousin marriage, for in 1839 he had married Emma Wedgwood, a woman who was both his first cousin and his sister-in-law. Persistent intermarriage between members of Darwin’s family and the Wedgwood clan effectively intertwined two bourgeois dynasties of the English Midlands. A plethora of biographical studies of the great evolutionist and the ongoing publication of his correspondence have revealed the particularities of this complex family network in great detail, with the result that more is perhaps known about Darwin’s extended family than that of any comparable figure (with the obvious exception of royalty). In Incest and Influence, an illuminating study of the significance of
Josiah Wedgwood married a cousin, but his children did not: His sons took a step up socially by marrying into the wealthy Allen family, and his daughter Susannah married Robert Darwin, the son of Josiah’s close friend Erasmus Darwin. In the next generation, Caroline Darwin married her cousin Joe Wedgwood. It was an alliance that made good financial sense, since her father, Robert, who was a private banker as well as a physician, had lent a lot of money to Joe’s father, “Jos”; the marriage would keep important debts within the family. Caroline’s brother Charles Darwin later married Joe’s sister Emma, reinforcing the alliance. From Incest and Influence. 80
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cousin marriages for the 19th-century English bourgeoisie, Adam Kuper therefore uses Darwin as an exemplar of a more general tendency. The book opens with an account of Darwin’s protracted deliberation over whether and whom to marry. His choice of a close relation as his spouse was, as Kuper makes clear, entirely unexceptional for a man of his social position in England at that time: In the Victorian upper middle classes, more than 1 marriage in 10 was between first or second cousins. A similar number of marriages were between brothers- and sisters-inlaw, meaning that about 1 person in 5 married within the family circle. This emphasis on endogamy was an effective means for bourgeois families like the Darwin-Wedgwoods to sustain beneficial domestic connections and to safeguard the property and riches accrued from the nascent industrial economy. Great intermarried families therefore came to dominate trades such as ceramics (the Wedgwood family’s pottery was world famous) and banking (the largest bank in the world, the House of Rothschild, was a family firm, and many Quaker banking families, including the Barclays and the Gurneys, intermarried and eventually merged their banks). Unlike other scions of such families, Darwin took a keen interest in the scientific aspects of interbreeding and heredity. Throughout his career he remained acutely concerned as to “whether or not consanguineous marriages are injurious to man,” as he put it in the conclusion to the Descent of Man in 1871. Darwin thus plays a further part in Incest and Influence as one of the foremost proponents (along with his cousin Francis Galton) of a more empirical approach to questions of heredity. In 1870, Darwin participated in an attempt to get Parliament interested in collecting evidence to determine whether cousin marriages had “injurious consequences.” When the attempt failed, he designed a study to address the question and asked his eldest son, George, who was a mathematician and amateur genealogist, to carry it out. George Darwin consulted marriage records, studied genealogies of the peerage and landed gentry, sent out questionnaires to upper-middle- and upper-class families, and gathered statistics from mental asylums, eventually concluding that the proportion of patients in the asylums who were the offspring of first-cousin marriages (about 3 to 4 percent) was
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about what one would expect given his estimate that 3.5 percent of middle-class marriages were between first cousins. The only finding that gave him pause was that although 3 to 3.5 percent of the men at Oxford and Cambridge were the sons of first-cousin parents, only 2.4 percent of the men who rowed for those universities (and were thus presumably extremely fit) were the offspring of cousins. In the end, he found little evidence that interbreeding between cousins was injurious, at least in the middle and upper classes, and both his father and Francis Galton endorsed his conclusions. Curiously, as Kuper shows, for much of the 19th century the principal legal concern with so-called incest was actually over marriage with a deceased wife’s sister, which was prohibited by Scripture and did not become legal until 1907. It was only after the First World War that scientific opinion hardened decisively against cousin marriage. Interestingly, the most recent genetic studies, as Kuper remarks in the book’s coda, now generally concord with George Darwin’s view that the risks to the offspring of first-cousin marriages are well within the limits of acceptability—that is, so long as cousin marriages are not repeated over several generations. It is well known that Charles Darwin’s life was blighted by recurrent stomach complaints (which resembled the fatal ailments of his Wedgwood mother) and by persistent anxieties over the health of his own children. Like many biographers, Kuper endeavors to discern a clear link between Darwin’s putatively fretful domestic circumstances and his revolutionary scientific thought. He cites the following passage from Darwin’s 1868 work The Variation of Animals and Plants Under Domestication: The existence of a great law of nature is almost proved; namely, that the crossing of animals and plants which are not closely related to each other is highly beneficial or even necessary, and that interbreeding [i.e., inbreeding] prolonged during many generations is highly injurious. Kuper then speculates that Darwin “was bound to consider the implications for his own family. His scientific project and his personal concerns could hardly be separated.” Significantly, however, the phrase “closely related” in the above passage from Variation refers not to the crossing www.americanscientist.org
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of plant or animal “cousins,” but rather (as is clear from sentences that precede it but are not quoted by Kuper) to more unambiguously incestuous unions, such as a male animal “paired with his daughter, granddaughter, and so on” or “matching brothers and sisters, which is considered the closest form of interbreeding.” In fact, in a passage added to the second edition of Variation in 1875, Darwin insists that “consanguineous marriages, such as are permitted in civilised nations . . . would not be considered as close interbreeding in the case of our domesticated animals.” It is, I would suggest, only by blurring the distinctions between Darwin’s interest in “close interbreeding” (a deliberately precise phrase that he uses repeatedly in both On the Origin of Species and Variation) and his related but nonetheless distinct concern with “consanguineous marriages” that Kuper can sustain the assertion, made in the introduction to Incest and Influence, that Darwin’s apparent “personal obsession” with cousin marriage played a central role in “provoking revolutionary ideas about breeding and heredity.” Such unwarrantedly audacious claims and the book’s sensationally alliterative title (hardly anyone used incest to describe cousin marriage in the period under consideration) actually militate against what I consider its main insight in relation to Darwin and Victorian society more generally: that cousin marriage amongst the English bourgeoi-
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sie between the 1790s and 1910s was pervasive and entirely commonplace. Our own attitudes to such unions are, as Kuper acknowledges, perhaps more prejudiced than those of any previous period, and this contemporary abhorrence is no more based on unequivocal scientific grounds than was the Victorians’ seeming acceptance of the practice. Incest and Influence presents a richly detailed and fascinating picture of the distinctive family life of the Victorian bourgeoisie, which Kuper considers “one of the great neglected themes of nineteenth-century history.” This portrait affords a useful corrective to the excitable assumptions of many of Darwin’s biographers (most notably Adrian Desmond and James Moore) that his marital circumstances were so anomalous and worrying that they spurred on his researches even into the self- and cross-fertilization of plants. Gowan Dawson is Senior Lecturer in the Victorian Studies Centre at the University of Leicester. He is the author of Darwin, Literature and Victorian Respectability (Cambridge University Press, 2007) and coauthor of Science in the NineteenthCentury Periodical: Reading the Magazine of Nature (Cambridge University Press, 2004). Currently he is writing a new book titled “Show Me the Bone”: Fragmentary Fossils, Functionalist Palaeontology and the Reconstruction of Prehistoric Creatures in Nineteenth-Century British and American Culture. He is also general editor, with Bernard Lightman, of an eight-volume series, Victorian Science and Literature (forthcoming from Pickering and Chatto).
BIOLOGY
Life’s Lineages W. Malcolm Byrnes THE NEW FOUNDATIONS OF EVOLUTION: On the Tree of Life. Jan Sapp. xx + 425 pp. Oxford University Press, 2009. $99 cloth, $39.95 paper.
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ublished in the year of the 200th anniversary of Charles Darwin’s birth, The New Foundations of Evolution is concerned with a topic that is decidedly non-Darwinian: the evolution of microorganisms and the structure of the universal tree of life. This is not really surprising, given that the author is Jan Sapp, an eminent historian of science at York University in Toronto whose previous books have challenged the accepted paradigms of biology. His first, published in 1987,
was titled Beyond the Gene: Cytoplasmic Inheritance and the Struggle for Authority in Genetics, and he has written several others on such topics as the history of symbiosis and the evolution of evolutionary thought. Like these others before it, Sapp’s latest book is both penetrating and paradigm-shifting. In the first half of the book, Sapp presents a thorough history of microbiology and microbial evolutionary biology from the 1600s to the middle of the 20th century. This sets the scene for 2010 January–February
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the second half of the book, in which he recounts the compelling story of the efforts of Carl Woese, a microbiologist at the University of Illinois at UrbanaChampaign, to construct a universal tree of life using ribosomal RNA sequences. Woese, by constructing his tree, which divided life into three primary lineages or domains—archaea, bacteria and eukarya—rather than the traditional five kingdoms (plants, animals, fungi, protists and monera), and by abolishing the venerable prokaryote-eukaryote dichotomy (to Woese the term prokaryote was inappropriate and misleading), shook the very foundations of evolutionary thought. Sapp’s account here is often riveting as he tells how Woese gathered
evidence to support the tree, forged a successful collaboration with Otto Kandler of Germany, and encountered resistance from prominent scientists and scientific journals. But, wait, you might say; what about that earlier statement that microbial evolution is non-Darwinian? Didn’t Darwin discover the natural process by which all life evolves, in which natural selection acts on heritable variation within populations? How could any form of evolution, microbial or otherwise, be an exception to this rule? How could anything lie outside Darwin’s overarching evolutionary mechanism? In the preface to The New Foundations of Evolution, Sapp writes that “to come
This universal phylogenetic tree based on ribosomal RNA phylogenies appeared in “A Molecular View of Microbial Diversity and the Biosphere,” a key paper by Norman Pace that was published in 1997 (Science 276:734-740). Pace characterized the tree as “a rough map of the genetic core of the cellular lineages that led to the modern organisms (sequences) included in the tree.” From The New Foundations of Evolution. 82
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to grips with microbial evolution is to reconsider much of classical biology’s understanding of the processes of evolution, its imagery, methods, and doctrines.” That’s because Darwinism and the Modern Synthesis traditionally have focused on the origins of species of animals and plants, Sapp explains, whereas microbial evolutionary biology probes the earliest origins of life itself. It is largely concerned with “the evolution that occurred before organisms as we know them appeared.” It looks at such problems as how the cell and its parts evolved, and how the genetic code might have arisen. Furthermore, he writes, “transfers of genes, of gene clusters, and of whole genomes between distantly related taxonomic groups [through horizontal gene transfer and symbiosis] are fundamental processes in microbial evolution.” And they are processes that lie outside the Darwinian scheme, which assumes gradual, incremental change. As Sapp reveals, microbes have always been problematic for evolutionary biologists. From the very beginning, microbes were not considered appropriate for evolutionary study. Discovered by Antony van Leeuwenhoek (1632–1723), microorganisms (including protists) were initially all lumped together in a group called the “infusoria.” Darwin himself, interested primarily in the origin of species, ignored these inhabitants of the invisible world because it was not clear to him (just as it is not clear to us now) whether bacteria even existed as distinct species. When the Modern Synthesis was forged in the 1930s and 1940s, bacteria again were left out. They were thought to dwell in a murky, Lamarckian world outside the Darwinian realm. Now, in our age of comparative genomics, we know that bacteria and archaea can swap genes through horizontal gene transfer, and they apparently have done so extensively in the past. Thus the pesky microbes may once again be causing trouble, this time threatening to turn Woese’s nicely branching tree into a web of interconnecting lines. But the saving grace—the redeeming feature—of the tree that Woese built is this: It is based on the analysis of not just any nucleic acid, but of 16S ribosomal RNA (rRNA). And 16S rRNA is a component of one of the subunits of the ribosome, a highly complex structure involved in the translation of messenger RNA into protein. It lies at the core of the cell’s information-processing system,
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where it has direct and indirect interactions with myriad other proteins and RNAs. Its gene is thus a highly unlikely candidate for a horizontal transfer event. As Sapp explains, in the early 1970s Woese very deliberately chose to use ribosomal RNA in his comparative analysis. This was a brilliant (and extremely lucky) decision on his part. We now know that there are only about 50 genes that lie at the universal informational core of organisms and thus would be appropriate for constructing a tree. Because Woese chose to base his tree on rRNA, it has, at least in terms of its major branches, withstood the test of time. In the 1990s, University of Colorado biologist Norman Pace dramatically expanded the tree by including 16S rRNA sequences obtained directly from microorganisms in environmental samples. He did this by developing a method that circumvented the need to establish cultures. The universal phylogenetic tree that Pace published in 1997 is reproduced on page 82. There are still difficulties in rooting the tree, and in pinpointing when the last universal common ancestor lived and what it looked like, but many scientists who once expressed doubts about the tree now by and large accept its broad outlines. This comes through clearly in a 2005 book edited by Sapp— Microbial Phylogeny and Evolution: Concepts and Controversies, which contains chapters written by some of the earlier skeptics. Whereas The New Foundations of Evolution gives a history of microbiology and tells the story of the discovery of the universal tree, Microbial Phylogeny and Evolution answers the question, How do things stand now regarding the universal tree of life? What one sees is broad acceptance by many, with some debate over the details. It is nonetheless true that many biologists still believe in a dichotomous prokaryote-eukaryote division of life in which there are prokaryotes on one hand (bacteria and archaea, both of which lack a distinct nucleus) and eukaryotes on the other. Moreover, for many, the gut bacterium Escherichia coli still serves as the prototype for all prokaryotes. Sapp discusses this whole debate, describing the twists and turns it has taken over the years. Ernst Mayr (1904–2005), an icon of evolutionary biology, was one of a number of scientists who vigorously opposed Woese’s (and Norman Pace’s) suggestion that the catch-all term “prowww.americanscientist.org
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karyote” be banned from biology. Woese and Pace had made this suggestion based on 16S rRNA analysis and the fact that a number of other cellular features also differentiate archaea from bacteria: their cell-wall structure and transfer RNA structure, the fact that archaean RNA polymerases resemble those of eukaryotes more than those of bacteria, the presence of unique lipids in their cell membranes, and the presence of introns in their genes. But to Mayr, evolution was “an affair of phenotypes,” and the purpose of taxonomy was to serve as “an information storage and retrieval system.” For Mayr, a taxonomic system (a tree, if you will) that was based on molecular phylogenetics and thus ignored the huge morphological differences between prokaryotes and eukaryotes was nonsensical. But Woese argued that the primary aim of taxonomy from
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the time of Darwin has been to “encapsulate descent,” and that doing so—in this case by constructing a 16S rRNA tree—would automatically take care of information storage and retrieval. This disagreement between Mayr and Woese was a battle between titans over the very foundation of evolutionary biology. Sapp expertly describes this debate and others, and thereby brings alive the dynamism at the heart of one of the most significant revolutions in the history of biology. W. Malcolm Byrnes is associate professor of biochemistry and molecular biology at Howard University College of Medicine. His research is concerned with the structure and function of archaeal and bacterial metabolic enzymes. He currently is working on a book applying concepts from evolutionary and developmental biology and ecology to issues in bioethics and Christian theology.
BIOLOGY
On the Origin of Taxonomy Kristin Johnson NAMING NATURE: The Clash Between Instinct and Science. Carol Kaesuk Yoon. viii + 344 pp. W. W. Norton and Company, 2009. $27.95.
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ur ambivalent responses to the rise of modern science and technology are among the most fascinating things to study in the history of science. From Margaret Cavendish’s criticism of the experimental method in the 17th century to the rebellion of the so-called Romantics against the notion of objectivity, our culture has had a complex love-hate relationship with science. Champions of feeling, emotion and subjective knowledge as a path toward understanding the natural world have proved especially persistent critics of science. Naming Nature, by Carol Kaesuk Yoon, is a thought-provoking text that plays a new and fascinating tune on the old theme of objectivity versus subjectivity. Its subject is the history of biological systematics—the description, ordering and explanation of biological diversity. In Yoon’s rendition, subjectivity is rooted firmly in our instinct. She explains that neuroscience, anthropology and evolutionary biology now tell us that we are born with the remnants of an instinctive perspective on the liv-
ing world, which she calls the “human umwelt,” a vision “molded during our species’ days as hunter-gatherers.” This vision of a natural order is “thoroughly sensuous and wildly subjective,” Yoon says, and she maintains that the history of scientific taxonomy is really a “twohundred-year-long battle against the human umwelt.” In modern times, we have given up this instinctive perception of the order of nature in favor of letting scientists find a more objective, evolutionary order, with the result that we are now disconnected from nature: “We are so used to someone else being in charge of the living world that we have begun not to even see the life around us.” Yoon argues that in order to reconnect to nature (and save the planet) we must begin to “kindly” thumb our noses at science. Yoon notes that she had not planned to write a book like this. She began the project as a history of the science of classification that would show the triumphant march of scientific progress as taxonomists improved on the crazy orderings of the past. But as she researched the topic, her attempt to describe science’s constant march toward increasingly true 2010 January–February
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accounts of the natural order morphed— to her surprise—into a critique. I began to see that science was neither the best nor the only valid way to order and name the living world. Instead, I realized that the ordering and naming of life was and always had been, at its heart, something much more democratic, subversive to the dominion of science even, and much more interesting. I eventually came to see that science itself might be undermining the very thing it sought to perfect: humanity’s understanding of life. Before you dismiss (or praise) Yoon as a relativist and postmodernist, out to bring down science’s hegemony, consider her background. She holds a B.S. in biology from Yale and a Ph.D. in ecology and evolutionary biology from Cornell. “This was not,” she writes forcefully, “where I expected or ever wanted to land.” As she makes her argument about the role and importance of the human umwelt, Yoon traverses a wide territory. Anthropology makes an appearance in her discussions of studies of how nonWestern cultures classify animals and plants (much as the West does, it turns
out). Neuroscience provides evidence of the umwelt through studies of individuals who, as a result of damage to specific areas in the temporal lobe of the brain, have completely lost their ability to recognize and name living things. The history of systematics is chronicled in chapters on the heroes of classification, Carolus Linnaeus and Charles Darwin. Then, after devoting just three and a half pages to the period from 1859 to 1950, Yoon provides an entertaining account of 20th-century systematics and the rise of cladistics, which dealt the umwelt a death blow. Yoon’s unapologetic fascination with and belief in the human umwelt colors her interpretations of all of these stories. As a result, she inevitably runs into the problems typical of efforts to apply an overarching theory to a range of material. Systematists’ complex challenges in ordering life, including the endless debates over what a species is, are all attributed to their struggles with the umwelt. And, when things get nasty (as they certainly did in late-20th-century systematics), Yoon maintains that the vitriol and name-calling are all attributable to the fact that nothing less than the human umwelt is at stake. Moreover, she believes that the success of creationists—from “Soapy Sam” Wilberforce to
In their 1951 classification of the families and orders of living birds, Ernst Mayr and Dean Amadon acknowledge that there is debate over whether the African bird known as the turaco (pictured above) should be included with turkeys and pheasants in the order known as the Galli or instead belongs with cuckoo birds in the order Cuculi. They end up placing the turaco with the Cuculi but in a position near the Galli. Carol Kaesuk Yoon notes that Mayr and Amadon do not explain “why, in the face of a diversity of opinion, they deem that ordering best,” and concludes that in this and many other instances they are relying on “intuition, an impossible-to-articulate, unconscious sense of order—all the things that had served Linnaeus so well.” From Naming Nature. 84
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modern-day proponents of “intelligent design”—in battling evolution is chiefly due to the power of the human umwelt. And why have people resisted the idea that race is not biologically real? “The answer, yet again, is the umwelt.” Yoon’s reduction of complex historical problems to the umwelt reaches particularly frustrating proportions in her claim that there is a tight, causal link between our having turned over the task of naming to scientists and our having become disconnected from nature. That disconnect, she says, accounts for the fact that species after species has disappeared “with hardly anyone noticing or much caring.” As one might expect given her thesis, Yoon finds the “key to remedying all of this” in reclaiming the “apparently incorrect names and categorizations” created by nonscientists around the world and throughout history. “The living world is dying,” she writes, “but it’s not too late.” Her apocalyptic rhetoric not withstanding, Yoon does not convincingly establish that the rise of scientific taxonomy played any role in making people indifferent toward the extinction of species. Despite these problems, anyone teaching an undergraduate course on the history of science and looking for a way to make the history of systematics exciting will find the book very useful. Conversational, personal and provocative, it is precisely what’s needed. Students who are wrestling with the complex interplay between values and science will find it engaging. I suspect that most students will either love or hate the book’s argument, style, assumptions and conclusions. But that Yoon began as a committed fan of science should inspire some fascinating conversations as students themselves begin to acquire a more complex and nuanced understanding of science in modern society. Furthermore, Yoon’s book can be placed within a long tradition of questioning the assumptions and privileges of science (although nowhere does she acknowledge this tradition). Students could read Cavendish, Rousseau, Goethe and others, comparing these historical figures’ responses to the rise of science with Yoon’s story. Some questions for them—and us—to consider: When Yoon asks us to reclaim our umwelt by finding an organism and getting “a sense of it, its shape, color, size, feel, smell, sound,” is she asking us to do anything different than Thoreau did more than
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150 years ago? Are her motivations so very different from his? Did Thoreau’s ambivalence toward science—a feeling that allowed him similarly to question science’s authority even as he tried to obey its rules—arise from a different source than Yoon’s? And then students could discuss whether, just as each age needs its own version of Galileo and
Darwin, each age may need its own framework for pitting what is in one’s own mind (whether one attributes that to instinct or to innate ideas) against what the experts say is true. Kristin Johnson is an assistant professor in the Science, Technology and Society Program at the University of Puget Sound in Tacoma, Washington.
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Wild Animals from chicago
M AT H E M AT I C S
A Growing Affinity David T. Kung THE CALCULUS OF FRIENDSHIP: What a Teacher and a Student Learned about Life While Corresponding about Math. Steven Strogatz. xiv + 166 pp. Princeton University Press, 2009. $19.95.
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ake a minute to think back a few years—okay, maybe a few more than that—to your high school days. Think past the awkward dances, the tortured relationships, the overhyped football games, to your high school math teachers. Who were they? What were their lives like? What did they do when they weren’t teaching you how to factor, what a logarithm is or how to take derivatives? What are they up to now? Unlike many of us, Steven Strogatz can actually answer these questions, at least with regard to his high school calculus teacher, Don “Joff” Joffray. Strogatz shares those answers and much more in The Calculus of Friendship. Part biography, part autobiography and part off-the-beaten-path guide to calculus, this quick read details 30 years of correspondence between Strogatz (who is now Jacob Gould Schurman Professor of Applied Mathematics at Cornell University) and Joffray. Calculus, Isaac Newton’s ingenious invention for modeling change mathematically, serves as both text and subtext for the letters that pass between Strogatz and Joff. Focusing almost exclusively on questions of mathematics, these brief notes frame the unlikely friendship of a teacher and his star student. With the precision of an awardwinning mathematician and the clarity of a best-selling science author, Strogatz leads us on an excursion through some of the lesser-known mathematical sights—the ones usually reserved for the “members only” tour. All the while, we see the relationship between the two www.americanscientist.org
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men gradually change as they slowly (and I do mean slowly) break down the walls that appropriately separate teacher from student. The mathematics covered in these letters is impressive for such a short volume—and for an exchange with a high school math teacher. The two men discuss pursuit problems. For instance, a dog starting at (0,1) in the x,y plane chases a man running at the same speed along the x-axis, with the dog swerving in such a way that it is always running straight toward the man’s current location. What is the equation for the curve traced by the dog’s path? Strogatz regales Joff with a geometrical proof that the square root of 2 is irrational. He recalls Joff telling the class about a former student finding a formula for the nth term of the Fibonacci sequence (which begins 1,1,2,3,5,8,13, ... ):
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(1 + √5 ) n – (1 – √5 )n 2n √5 Then Strogatz provides a succinct twopage proof. One of Joff’s later students asks whether the series ∞ sin k
∑
k converges, leading to a discussion of Fourier series (and the surprising sum of the series). Although the pair’s mathematical excursions pay off every two or three pages, the story of their relationship takes longer to develop. Five chapters into the book, you may feel like responding to the book’s subtitle—What a Teacher and k =1
Mr. Jefferson and the Giant Moose Natural History in Early America Lee Alan Dugatkin “Lee Alan Dugatkin introduces you to Thomas Jefferson and the giant moose, an animal so great and imposing that never again could the belittling naturalists of Europe assume that American natural life was inferior.” —Michael Ruse, author of Darwinism and Its Discontents Cloth $26.00
The University of Chicago Press www.press.uchicago.edu
2010 January–February
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In 1999 Cornell mathematician Steven Strogatz (right) paid tribute to his high school mathematics teacher Don “Joff” Joffray (left) at an event held to celebrate teaching and to honor Joffray, who was about to retire. From The Calculus of Friendship.
a Student Learned about Life While Corresponding about Math—with a resounding “Nothing!” Only Strogatz’s criticisms of the younger, more self-absorbed version of himself keep this strand of the story
alive, as when he admits the shame of never having acknowledged the death of Joff’s oldest son. Over the years, their correspondence begins to include news of their lives along with the interesting mathematical tidbits. This broadening of their relationship comes just in time—another cold mathematical exchange might have convinced us that mathematicians hail not from Mars or Venus but from Pluto. In the last few chapters, the two men write (and in some cases talk) about Strogatz’s career path, Martin Gardner’s mountainclimbing-monk problem, Joff’s windsurfing, a clever use of dimensional analysis, Joff’s teaching award, and where to put the fuel gauge marks for a cylindrical gas tank. The growing affinity of these two for each other as people, and not just as sources of mathematical knowledge, provides a more interesting frame for the stillcaptivating mathematical excursions. Eventually Strogatz works up the nerve to travel to Joff’s home to dis-
PHYSICS
Livin’ la Vida Micro Thomas R. Powers LIVING AT MICRO SCALE: The Unexpected Physics of Being Small. David B. Dusenbery. xxxii + 416 pp. Harvard University Press, 2009. $49.95.
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illions of years of evolution have shaped the strategies that microorganisms use for locomotion and feeding. Although evolution of successful biological strategies is driven by competition among organisms or by changes in the environment, all strategies must respect the constraints of physics. By studying the distinctive physics of the “micro world”—a realm invisible to the naked eye, made up of objects smaller than about 0.1 millimeter—one may determine what strategies are possible for microorganisms and which of those are optimal. David Dusenbery’s book Living at Micro Scale does an excellent job of explaining the physics that is relevant at this scale and, later in the book, how this physics affects the behavior of microorganisms. As Dusenbery makes clear, the physics of the micro world is different from the familiar physics of our everyday experience. An important theme is that
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water is effectively very viscous at the micro scale, which may seem counterintuitive, given that viscosity is a material property. But it turns out that the characteristic length and velocity scales of a flow are important for determining whether that flow is viscous. For example, the viscosity of air is not something we usually notice, but if you were to try breathing through a straw and then replacing that straw with a series of thinner ones, you would find it increasingly difficult to breathe. This reflects the fact that the narrower the straw is, the more important viscous forces become. To determine quantitatively whether viscous effects are significant, you must measure them against something else. The natural comparison to make is between the typical viscous forces acting on a body and the inertial forces required to cause the body to undergo a given acceleration. The ratio
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cuss some of the personal things their letters glossed over. An account of the visit brings the book to a satisfying, if slightly sappy, conclusion. Finally the author’s nonmathematical observations rise to the level of his mathematical ones, as in this wonderful passage about the complicated relationship between a teacher and a gifted student: I’m starting to realize what it was that he gave me. He let me teach him. Before I had any students, he was my student. Somehow he knew that’s what I needed most. And he let me, and encouraged me, and helped me. Like all great teachers do. As every educator knows, in the relationship between teacher and student, the learning happens in both directions. David T. Kung is associate professor and chair of the department of mathematics and computer science at St. Mary’s College of Maryland. His interests include harmonic analysis, math education and the violin.
of the typical inertial force to the typical viscous force is called the Reynolds number. For a bacterium about 1 micrometer in diameter swimming in water at a speed of 10 micrometers per second, the Reynolds number is 10–5. All other things being equal, as the size of a body decreases, the viscous forces per unit volume increase more rapidly than do the inertial forces per unit volume. A microorganism thus encounters viscous forces that are huge compared with the inertial forces it experiences. Inertia is therefore irrelevant at the micro scale. To get a sense of what swimming is like for a bacterium, imagine swimming in tar. The bacterium has to use drag to swim. In contrast, efficient human swimming relies on coasting, which is only possible when viscous forces are small compared with inertial forces. A person 2 meters tall swimming at 1 meter per second has a Reynolds number of 2 × 106. The fact that we don’t experience the dramatically small Reynolds numbers with which bacteria have to contend helps explain why we find the micro world so strange. Dusenbery also gives other examples of surprising phenomena related to viscosity. For instance, in a highly viscous environment, the drag on a thin filament is roughly the same as the drag on a sphere with a diameter equal
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to the length of the filament. He also points out that waving a rigid oar back and forth in highly viscous fluid doesn’t get you anywhere. Dusenbery ties the physics of these things nicely to biological observations, presenting physical arguments to explain why the swimming appendages of microorganisms tend to be filaments rather than paddles, and why motile bacteria tend to be larger than those that just float about. A second major theme of Dusenbery’s book is that diffusion transports and reorients molecules more rapidly than do the typical flows found at the micro scale. Again, this physical fact leads to unexpected consequences. For example, the rate at which randomly diffusing molecules bump into the surface of a cell is proportional to the diameter of that cell, and not its surface area. Also, because microorganisms tend to drag a halo of fluid with them as they move, bacteria cannot increase the collision rate of molecules at their cell surfaces by swimming. The physics of diffusion and viscous flow leads to size limits for biological processes such as gravity sensing, pheromone detection and guidance by heat or chemicals. These limits are summarized in the figure on this page. Note that many of the critical values are close to one micrometer, which (as Dusenbery explains) is because these limits depend on just a few parameters: temperature, viscosity and the energy density of organisms. The author’s account of how these size limits are calculated and how the behavior of real organisms conforms to them is one of the most fascinating parts of the book. Dusenbery sketches the history of the development of scientific techniques and ideas such as microscopy, molecular theory and information theory. These passages remind the reader that powerful ideas can drive scientific progress in disparate fields. For example, he describes how the 19th-century botanist Robert Brown showed that any type of particle that is sufficiently small exhibits constant random motion when suspended in water, and that this is a physical rather than a biological phenomenon. Subsequent work by Einstein and others on this Brownian motion made the existence of molecules undeniable and set the stage for the study of macromolecules. Likewise, the same statistical ideas that were important for describing Brownian motion proved useful for Claude Shannon’s www.americanscientist.org
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formulation of information theory. And Shannon’s ideas have in turn proved useful in understanding the limitations on what microorganisms can find out about their environments. Dusenbery also recounts some of his own scientific discoveries. These passages show the many connections between different areas of science and illustrate its human elements. Dusenbery has supplied everything a reader might need to understand
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the ideas he presents in the book, including 12 appendices, which explain such topics as sedimentation equilibrium, the chemical potential and the mathematics of ellipsoids. Two of these appendices even review calculus and simple approximation rules. The mathematical nature of physics is hard to avoid, and it is hard to imagine that a reader who needs such a review will be able to follow some of the more complex mathematical arguments in
The physics of the world of microorganisms differs from what we are accustomed to in our everyday experience; for example, inertia plays no role, and Brownian motion is often important. Taking such factors into account, David B. Dusenbery has made quantitative estimates of a variety of limits on the size at which organisms can accomplish certain tasks; these are summarized in the figure above. The size scale in meters is on the left, and vertical lines show the range of lengths of major groups of organisms. The horizontal lines to the right of these vertical lines show the size limits for such organism functions as swimming faster than diffusion. Many of the size limits cluster around a diameter of 1 micrometer. From Living at Micro Scale. 2010 January–February
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the book. Nevertheless, the author obviously has put a lot of work into finding simple, intuitive explanations for many of the physical and mathematical concepts he describes. As a result, the book will be accessible and useful to a wide audience of people interested in biology, physics or engineering. And the provocative questions
presented are sure to be the subject of intense activity in the research community for years to come. Thomas R. Powers is associate professor of engineering at Brown University. His research interests include locomotion at low Reynolds numbers and the physics of soft matter, such as polymers, membranes and liquid crystals.
M AT H E M AT I C S
Never a Dull Number Brian Hayes THOSE FASCINATING NUMBERS. Jean-Marie De Koninck. xviii + 426 pp. American Mathematical Society, 2009. $49.
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t all begins with a taxi ride. In 1918 the Cambridge mathematician G. H. Hardy goes to visit his protégé Srinivasa Ramanujan and mentions that the number of his taxicab was rather dull: 1,729. Not dull at all, Ramanujan replies; 1,729 is the smallest number that can be written as the sum of two cubes in two different ways (123 + 13 and 103 + 93). From this famous anecdote springs a mathematical joke. If 1,729 is not a dull number, then which numbers are dull? In particular, what is the smallest number that has no interesting traits—nothing to make it stand out in the endlessly receding line of undistinguished integers? The joke is this: Whatever number you choose as the smallest dull number immediately becomes highly interesting because it’s the smallest dull number. Those Fascinating Numbers, a collection of numerical lore by Jean-Marie De Koninck, can’t escape the pseudoparadox of dull numbers. The book is essentially a list of the counting numbers, presented in the usual order, with notes on curious facts about each of them: 1 is the only number that divides all the others; 2 is the only even prime number; 3 is the smallest triangular number. Clearly, this can’t go on forever. And so one is led to ask: What is the first number that De Koninck skips over in his enumeration—the smallest number for which he could find no facts worth mentioning? I’ll give the answer at the end of this review; for now I’ll just note that the first omission in the sequence follows an integer identified as “the seventh number whose sum of divisors 88
is a perfect square.” You’re welcome to work that out, if you’d like. What makes a number interesting? This is a question each of us must answer for ourselves; tastes differ. De Koninck, a mathematician at the University of Laval in Quebec, gives much attention to the divisors of numbers and to patterns in their decimal digits. For example, the entry for 153 points out that it is one of just five numbers equal to the sum of the cubes of its digits; and 26 is distinguished as the smallest number that is not a palindrome but whose square is a palindrome. These are not properties that excite my personal sense of wonder. On the other hand, I was intrigued by the observation that 70 is “the only number whose square corresponds to the number of cannonballs one can pile up in a pyramidal shape (702 = 12 + 22 + . . . + 242).” And I’m glad to know that 1,368 is the number of ways you can fold a 3-by-3 sheet of stamps. This is a book for browsing rather than sustained reading. It would make an excellent online resource, since searching and following cross-references would be more convenient. And it’s the kind of book that ought to be kept on hand in barrooms or coffee shops where the numerati hang out, an authority for settling arguments and wagers over the second-smallest number that can be written as the sum of two cubes in two different ways (4,104) or the smallest dull number according to De Koninck (95). Brian Hayes is Senior Writer for American Scientist. He is the author most recently of Group Theory in the Bedroom, and Other Mathematical Diversions (Hill and Wang, 2008).
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Statement of ownership, management and circulation (required by 39 U.S.C. 3685). 1. Publication title: American Scientist. 2. Publication number: 0023-240. 3. Filing date: October 1, 2009. 4. Issue frequency: Bimonthly. 5. No. of issues published annually: 6. Annual subscription price: $28. 7. Complete mailing address of known office of publication: P.O. Box 13975, Research Triangle Park, NC 27709-3975. 8. Complete mailing address of headquarters or general business office of publisher: P.O. Box 13975, Research Triangle Park, NC 27709-3975. 9. Full names and complete mailing addresses of publisher, editor, and managing editor: Dr. Jerome Baker, publisher, P.O. Box 13975, Research Triangle Park, NC 27709-3975; David Schoonmaker, editor, P.O. Box 13975, Research Triangle Park, NC 27709-3975; Morgan Ryan, managing editor, P.O. Box 13975, Research Triangle Park, NC 27709-3975. 10. Owner: Sigma Xi, The Scientific Research Society, P.O. Box 13975, Research Triangle Park, NC 27709-3975. 11. Known bondholders, mortgagees, and other security holders owning or holding 1 percent or more of total amount of bonds, mortgages, or other securities: None. 12. The purpose, function, and nonprofit status of this organization and the exempt status for Federal income tax purposes: Has not changed during preceding 12 months. 13. Publication Name: American Scientist. 14. Issue Date for Circulation Data: Sept/Oct 2009. 15. Extent and nature of circulation: A. Total no. copies: average no. copies each issue during preceding 12 months, 101,546; actual no. copies of single issue published nearest to filing date, 91,941. B. Paid and/or requested circulation: B1. Paid/requested outside-county mail subscriptions stated on Form 3541: average no. copies each issue during preceding 12 months, 57,404; actual no. copies of single issue published nearest to filing date, 42,068. B2. Paid in-county subscriptions: average no. copies each issue during preceding 12 months, 0; actual no. copies of single issue published nearest to filing date, 0. B3. Sales through dealers and carriers, street vendors, counter sales, and other non-USPS paid distribution: average no. copies each issue during preceding 12 months, 13,696; actual no. copies of single issue published nearest to filing date, 13,743. B4. Other classes mailed through the USPS: average no. copies each issue during preceding 12 months, 0; actual no. copies of single issue published nearest to filing date, 0. C. Total paid and/or requested circulation: average no. copies each issue during preceding 12 months, 71,100; actual no. copies of single issue published nearest to filing date, 55,810. D. Free distribution by mail: D1. Outside-county as stated on Form 3541: average no. copies each issue during preceding 12 months, 532; actual no. copies of single issue published nearest to filing date, 528. D2. In-county as stated on Form 3541: average no. copies each issue during preceding 12 months, 0; actual no. copies of single issue published nearest to filing date, 0. D3. Other classes mailed through the USPS: average no. copies each issue during preceding 12 months, 0; actual no. copies of single issue published nearest to filing date, 0. E. Free distribution outside the mail: average no. copies each issue during preceding 12 months, 1,076; actual no. copies of single issue published nearest to filing date, 1,125. F. Total free distribution: average no. copies each issue during preceding 12 months, 1,608; actual no. copies of single issue published nearest to filing date, 1,653. G. Total distribution: average no. copies each issue during preceding 12 months, 72,708; actual no. copies of single issue published nearest to filing date, 57,463. H. Copies not distributed: average no. copies each issue during preceding 12 months, 28,838; actual no. copies of single issue published nearest to filing date, 34,478. I. Total: average no. copies each issue during preceding 12 months, 101,543; actual no. copies of single issue published nearest to filing date, 91,941. Percent paid and/or requested circulation: average no. copies each issue during preceding 12 months, 98 percent; actual no. copies of single issue published nearest to filing date, 97 percent.
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Nanoviews EARLY SPRING: An Ecologist and Her Children Wake to a Warming World. Amy Seidl. Beacon Press, $24.95.
STORIES IN STONE: Travels Through Urban Geology. David B. Williams. Walker & Company, $26.
When life circumstances forced David B. Williams to give up the canyons of Utah for the streets of Boston, he turned to architecture for solace—in particular, to the granite that characterizes so many of the city’s structures, including the Bunker Hill Monument. A geologist by training but a natural history writer by profession, Williams wondered where the monument’s rock had been quarried, which took him to Quincy, Massachusetts, also known as the Granite City. That conceit—pursuing the provenance of a building material—becomes his jumping off point for stories of geology and history. With nine other rocks to serve as chapters, a book gets built. I admire the cleverness of Williams’s device, but it would have failed were he not such a fine storyteller. No rock he picked was new to me, but nearly every tale was. It came as no surprise that St. Augustine’s Castillo de San Marcos is built of coquina, but I had no idea it was so resistant to cannon fire—or that it had allowed the Spanish to withstand multiple English sieges. His explanation of why Carrara marble proved to be an unfortunate choice for cladding Standard Oil’s Chicago headquarters is unusually clear and yet lyrical. What else would you expect from a science observer who includes a visit to Robinson Jeffers’s (granite) Hawk Tower (above) in his book on rocks?—David Schoonmaker
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It’s tempting to see the convergence of literature and ecology as a Mary Poppins scenario: A spoonful of lyrical prose helps the data go down. But science writing only feels like medicine when it’s done without consideration for the reading audience. Books filled solely with lyrical ramblings about one’s place in the natural world can be pretty good, depending on who’s doing the rambling. But there are plenty of sickly-sweet examples that leave us wishing the author had bothered to fact-check his species names. And even the best such writing is enriched by thoughtful exploration of the precepts and findings of environmental science. The present wealth of ecological memoirs adds up to a collective learning experiment—one that joins up science, art and human beings’ intuitive responses to the living world. Amy Seidl’s book Early Spring is a fine addition to the genre. Seidl’s passion for scientific detail is matched by her concern for her relationship to the land and for her children’s experience of the natural world. She tells of looking through a microscope at pollen grains from successive periods of history and deftly relates this to the effects of climate change on forests and the culture of maple syrup making in Vermont, where she and her family live. She discusses how warmer temperatures affect seasonal patterns of flower blooming and muses about how this may affect the life cycles of butterflies. In chapter after chapter, we find Seidl’s thoughtful assimilation of data from scientific studies and from individuals who monitor local weather patterns over years, as well as the careful observations of a thinking and feeling human being about the land she lives on. Maybe that’s what allows scientific study and creative writing, so often consigned to their separate corners, to be synchronous—the deep attention that each requires, different in kind but similar in requirements: focus, precision, awareness of context, love. Readers who are
concerned about both landscape and climate change, writers who hope to contribute to the genre, and the land itself will all be beneficiaries of Seidl’s work.—Anna Lena Phillips AM I MAKING MYSELF CLEAR?: A Scientist’s Guide to Talking to the Public. Cornelia Dean. Harvard University Press, $19.95.
Am I Making Myself Clear?, by New York Times science writer Cornelia Dean, is a guidebook for scientists on talking to the public. It expands on a series of science-communication seminars that Dean delivered to a Harvard audience, although she’s careful to say that her small volume is not scholarly, technical or thorough. Rather, she has aimed to create a useful guide, one with helpful pointers for researchers who interact with policymakers, the public and journalists. She succeeds at meeting this important goal: The book brims with insight and expertise based on a career at the pinnacle of science journalism. Dean’s easy style and casual authority are irresistible, and research scientists and engineers will realize quick benefits from such a practical, illuminating guide. But creating something useful was only the first of her two goals in writing the book—and the less important one at that. The greater mission, as Dean lays out in the introduction, was to “convince researchers that communicating their work and the work of others to the lay public is important for society—and a valuable use of their time.” She skillfully marshals facts and narrative to support this proposition, and as part of the choir to whom she is preaching, I found her arguments compelling. There are important reasons to broaden the expectations for scientists so that some form of public engagement becomes a professional obligation. But there are significant obstacles too, including the inertia of the established culture of science and institutional practices that fail to reward—and sometimes even penalize—such engagement. It’s too soon to tell whether her call to action, added to similar calls from Al Gore, Bruce Alberts and Alan Leshner (among others), will tip the balance.—Chris Brodie
2010 January–February
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Sigma Xi Distinguished Lecturers 2010–2011
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or the 72nd consecutive year, Sigma Xi presents its panel of Distinguished Lecturers as an opportunity for chapters to host visits from outstanding individuals who are at the leading edge of science. These visitors communicate their insights and excitement on a broad range of topics. Each year thousands of Sigma Xi members, students and the public have an opportunity to hear exceptional talks and to ask questions of these experts. The 2010–2011 Distinguished Lecturers are available July 1, 2010–June 30, 2011. Each visitor has consented to a modest honorarium together with full payment of travel costs and subsistence. Local chapters may apply for subsidies to support expenses related to hosting a Distinguished Lecturer. Applications must be submitted online by March 1 for funds to be available the next fiscal year. The Committee on Lectureships is pleased to announce the support of the American Meteorological Society, the National Academy of Engineering, the National Academy of Sciences, the National Cancer Institute and the Society for Risk Analysis. These sponsors nominate a member of their society as a lecturer, and provide funding for additional subsidies. Lecturer biographies, contact information, abstracts of talks and additional program information can be found online under the Lecturership Program link at www.sigmaxi.org. For additional information please send an email to
[email protected] or call 800-243-6534 x206. _________________ The Distinguished Lectureship Program supports the mission of Sigma Xi to promote the health of the research enterprise and the public understanding of science. Willie Pearson, Chair Committee on Distinguished Lectureships
Gary D. Christian, Professor of Chemistry Emeritus, University of Washington A Brief History of Analytical Chemistry: From the Beginnings to Modern Analytical Science (S) • The Ethics of Scientific Writing: How to Write and How Not to Write a Paper (G) • The Physiology and Chemistry of Breath Alcohol Measurement. Or, Are You Too Drunk to Drive? (P)
David W. Frayer, Professor, University of Kansas Neandertals and Us (P,G,S) • The Krapina Neandertals: What They Tell Us About Neandertal Behavior? (P,G) • Homofloresiensis: The Hobbit Tale (P,G) • Teeth: Repositories of Prehistoric Human Behavior (G,S)
S. Douglass Gilman, Associate Professor of Chemistry, Louisiana State University Protein Aggregation and Disease: Is Chemical Analysis up to the Challenge (G,S) • Microfluidics and Chemistry: Why a Bioanalytical Chemist Dabbles in Fluid Dynamics and Magnetics (G,S) • Studying Enzyme Inhibition with Electrophoresis - Migrating Through the Chemist’s Bucket (G,S) P (Public), G (General), S (Specialized)
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Michael F. Goodchild, Professor of Geography, University of California, Santa Barbara Where are we now? An Assessment of GPS (P) • The Spatial Web: Visions for a Geospatial World (G) • Fundamental Spatial Concepts (S)
Paula Hammond, Bayer Professor of Chemical Engineering, Executive Officer - Department of Chemical Engineering, Massachusetts Institute of Technology Nanolayer Assembly Approaches to Biomedical Materials and/or Electrochemical Devices (G,S) • Self Assembly of Responsive Thin Films (G,S) • Nanoscale Assembly for Targeted Drug and Gene Delivery (G,S)
Wesley L. Harris, Professor and Associate Provost, Massachusetts Institute of Technology Fluid Dynamics of Diffusion in Blood Microcirculation (S) • Grand and Not-So Grand Challenges for Engineering (G) • The Face of American Science (P,G,S)
Details available at http://www.sigmaxi.org/programs/lectureships/index.shtml
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Evelyn L. Hu, Professor, School of Engineering and Applied Science, Harvard University Michelangelo’s Laser (G,S) • Creating Solar Cells with Viruses (G,S)
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Laurie E. Locascio, Chief of the Biochemical Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology Biological Applications of Microfluidics (P,G,S)
Terry L. Hunt, Professor in the Department of Anthropology, University of Hawaii-Manoa What (Really) Happened on Easter Island? Ecological Catastrophe and Cultural Collapse (P,G,S) • Theory of Bet-Hedging Points to Ancient Easter Island’s Success (G,S) • Megaliths Made to Move (G,S) • Ancient Human Impacts on Land and Sea in Polynesia (G)
Gregory M. Paoli, President, Decisionalysis Risk Consultants, Inc. Term begins January 1, 2010. Please visit www.sigmaxi.org for a biography, lecture topics and contact information of this speaker
Marc L. Imhoff, Earth Scientist - Aerospace Technology, National Aeronautics and Space Administration
Howard Pinderhughes, Associate Professor and Chair, University of California, San Francisco
Gray Wave of the Great Transformation: A Satellite View of Urbanization, Climate Change, and Food Security (P,G,S) • Planetary Secrets: The Secret Lives of Storms, Deserts, and Fires (P,G,S) • Human Appropriation of Net Primary Production—Can the Earth Keep Up? (P,G,S) • How Has Urbanization Altered the Carbon Cycle in the United States? (S)
Dealing With Danger: How Innercity Youth Cope With the Violence that Surrounds Them (P,G) • Racial Identities, Attitudes and Conflict Among Youth (P,G) • Love Is Blind: Relationship Violence Among Inner City Youth (P,G)
Jessica M. Nunez de Ybarra, Public Health Medical Officer III, California Department of Public Health
William N. Ryerson, President, Population Media Center - Shelburne, Vermont
The Public Health Approach (P,G,S) • The Work of Public Health: A California Example (P,G,S) • The People in Public Health (P,G,S) • The Challenges of Public Health (P,G,S)
Solving the World’s Social and Environmental Problems through Soap Operas (P,G,S) • Sex, Soap Operas and Social Change (P) • Role Modeling by the Mass Media in Shaping Health and Environmental Behaviors (P,G) • Application of Albert Bandura’s Social Cognitive Theory to Practical Issues of Reproductive Health and Population Trends in Developing Countries (S)
American Meterological Society Sigma Xi Lecturer
Francisco J. Samaniego, Professor of Statistics, University of California, Davis
Bette L. Otto-Bliesner, Senior Scientist, National Center for Atmospheric Research
Bayesian vs. Classical Statistics: The History, the Debate and a Recommendation Solution (G,S) • From the X Files (and the Y Files) of the Statistical Laboratory at the University of California, Davis (P,G,S) • Comparing Engineered Systems (G,S) • Statistical Issues in Gambling, Extra Sensory Perception and Lie Detector Tests (P)
Climate Change: What Could Happen and What Can Earth’s Past Tell Us? (P,G) • Warmth at the Poles and Sea Level Rise (G,S) P (Public), G (General), S (Specialized)
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Society for Risk Analysis Sigma Xi Lecturer
Details available at http://www.sigmaxi.org/programs/lectureships/index.shtml
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National Academy of Engineering Sigma Xi Lecturer
National Academy of Engineering Sigma Xi Lecturer
Maxine L. Savitz, VP, National Academy of Engineering
Alissa Weaver, Assistant Professor, Vanderbilt University
Increasing Energy Efficiency: Expanding the Opportunities (P,G) • America’s Energy Future: Technology Opportunities, Risks and Tradeoffs (P,G)
How Physical Properties of the Extracellular Matrix Affect Cancer Invasion (G,S) • Integration of Experimental Data and Mathematical/Computational Science: The Whole is Greater than the Sum of Its Parts (P,G,S) • In Silico Experiments Provide Insight into Cancer Progression Mechanisms (P,G,S)
Robert Strongin, Professor of Chemistry, Portland State University Striving for the Simplest Possible Means of Detecting Disease (G,S) • How to Design a Molecular Light Bulb and Related Broadband Organic Fluorophores (G,S) • Chemistry, Medicine and Society—Perspective of a Basic Scientist (P,S)
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P (Public), G (General), S (Specialized) Details available at http://www.sigmaxi.org/programs/lectureships/index.shtml
Application Deadline: March 1, 2010 http://www.sigmaxi.org/programs/lectureships/index.shtml
Donate Your Back Issues Sheryl A. Tucker, Associate Dean of the Graduate School and Professor of Chemistry, University of Missouri The Pipeline: Igniting Children’s Interest in Science (P,G,S) • From Having a Pet to Working with a Vet (P,G,S) • Understanding and Harnessing Molecular Containers (G,S)
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January-February 2010 · Volume 19, Number 1
Crosby Elected Sigma Xi President ichael P. Crosby
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was elected the 74th president of Sigma Xi at the Society’s 2009 Annual Meeting in The Woodlands, Texas. He will serve as presidentelect in FY 2011. He is the interim vice chancellor for research and economic development at the University of Hawaii at Hilo and is currently on leave from his position as executive director for the National Science Board. Crosby has more than 30 years of research, teaching, science management and leadership experience. During much of the past 20 years, he has played an active role in leading national and international multi-disciplinary research programs, as well as developing national policy and administrative aspects for our country’s science programs. He has held a number of positions with the National Oceanic and Atmospheric Administration (NOAA), including senior advisor for international science policy. He also served as executive director for the NOAA Science Advisory Board, national research coordinator for ocean and coastal resource management and chief scientist for sanctuaries and reserves. Prior to joining NOAA, he held numerous faculty positions with the Baruch Institute for Marine Biology and Coastal Research at the University of South Carolina, the Department of Marine Science at Coastal Carolina University, the Graduate Program at the University of Charleston, and Salisbury State University. He has also had previous positions with the National Marine Fisheries Service, the U.S. Army Corps of Engineers and the National Cancer Institute. Crosby obtained an M.S. in biology from Old Dominion University and a Ph.D. in marine-estuarine-environmental sciences at the University of Maryland. He is a member of Sigma Xi, National Shellfisheries Association, Estuarine Research Federation and is a fellow of the Royal Linnean Society of London. He is also on the board of governors for the U.S.-Israeli Binational Science Foundation and the board of directors for the Pacific Congress on Marine Science and Technology. • www.sigmaxi.org
American Scientist
From the President The Meaning of Membership What does membership in Sigma Xi mean? The single major issue confronting Sigma Xi today is membership. Like many of our brother scientific societies, we face erosion in our membership, which is fueled by both the aging of our membership base and our inability to induct and maintain the next generation of scientists as members. I serve Sigma Xi today because of my commitment to the value and role that I hold for Sigma Xi, both in the scientific endeavor and in my personal life. However, to deal with the issues at hand, I have attempted to step out of my level of comfort with Sigma Xi and ask the question what does membership in Sigma Xi mean? I don’t pretend to have the answers, but I do hope this will initiate the debate. Sigma Xi was founded as a chapter-based honor society for science and engineering, which grew and flourished on the model that camaraderie and collegiality combined with the desire to improve and support the scientific enterprise would attract and fulfill generations of scientists and engineers. Sigma Xi became known for its recognition of excellence and honor in science, its support of ethics in science, its involvement in promoting the understanding of science, scientific literacy and the appreciation of the scientific method, and for its support of young scientists through its Grants-inAid program and through mentoring of young scientists. Have our values changed so radically that these goals are no longer relevant to the next generation of scientists, or have we simply not delivered on the promise of Sigma Xi? Is it the model or the implementation of the model that is causing our membership problem? While the model for Sigma Xi was built around chapter membership, it is clear that we each have our own personal reason for accepting and continuing our relationship with Sigma Xi. For example, the fastest growing constituency in Sigma Xi is the members-at-large category, where there is no chapter association at all. Furthermore, many members will remain active after leaving even a successful chapter without moving their affiliation to a new chapter in their area. Finally, we see that many members retain their active status even if their own chapter fails to meet the basic standards required to remain in good standing. This dichotomy between chapter association and membership is striking and raises a number of questions. What are the personal benefits that keep members active outside of chapters? Is it our belief in the mandates of Sigma Xi, regardless of the presence of a chapter to support our values, that fulfills our needs? Is it, as our Executive Director Jerry Baker points out in his report to the annual assembly of delegates, because of what membership in Sigma Xi says about you? Membership in Sigma Xi doesn’t define your area of scientific research but rather speaks to the values you hold as a person and as a scientist and of your personal commitment to science and engineering. The personal, tangible value of membership in Sigma Xi is very real for each of us, and therefore we must look at the sustainability of the Society we have chosen to represent our goals and values. This brings us full circle to a discussion of membership. Membership is generally considered a chapter activity and for the most part it is. We induct students and honor them with membership to initiate their growth toward becoming committed scientists and engineers. However, I would like to encourage the concept of the individual’s role and responsibility in sustaining Sigma Xi. I further encourage you to personally reach out to kindred spirits and honorable colleagues to bring them into a society that you value and support. Share your reasons for supporting Sigma Xi and share not only your values with the next generation of scientists and engineers but also the opportunity for them to become involved and make a difference. Howard Ceri 2010 January-February 93
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Awards Recognize Outstanding Sigma Xi Chapters
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ertificates of Excellence were awarded to six Sigma Xi chapters at the 2009 Annual Meeting and International Research Conference. The annual awards recognize exceptional chapter activity, innovative programming and community leadership during the past fiscal year. Nominees are chosen by the Constituency Directors based on chapter annual reports, and winners are selected by the Committee on Qualifications and Membership. Award-wining chapters for 2009 included Charleston, Duke University, Ohio State University, Purdue, Research Triangle Park and University of California, Merced.
Program Awards Also presented at the Annual Meeting, Chapter Program Awards recognize chapters for a single outstanding program, especially one that other chapters can emulate. Nominees are chosen by the Regional Directors based on chapter annual reports, and winners are selected by the Committee on Qualifications and Membership. 2009 Program Awards went to Rice University-Texas Medical Center for creating the DREAM (Designing with Rice Engineers) STEM Diversity through Mentorship Outreach Program, in which Rice University STEM undergraduates mentor and teach students at three Houston public schools. Research Triangle Park was honored for its Science Café program; Duke University, for partnering with WiSE to
sponsor a Women’s Networking Event at ScienceOnline’09; and the Mayo Foundation, for developing a promotional video to showcase the founding of its chapter, the mission and the benefits of Sigma Xi membership. Also receiving Program Awards were the Claremont Colleges, for hosting an
ice cream social designed to increase student involvement in the chapter and to foster communication between the members at the five colleges; Northwestern University, for its Junior Science Café program, geared toward middle and high school students and their parents, teachers and grandparents.
Diversity Awards Diversity Program Awards are presented annually to chapters that have organized outstanding programs to promote diversity within the science, engineering and research communities. Nominees are chosen by the Regional Directors based on Chapter Annual Reports and Diversity Award applications. Winners are chosen by the Society’s Diversity Committee. This year the committee singled out Rockefeller University for its efforts to increase awareness in the sciences, especially in the under-resourced and underrepresented sections of our society. The chapter has been working closely with the Harlem Children Society over the past several years with outstanding results. The aim of these efforts is to increase awareness in the sciences, engineering and mathematics and provide opportunities for students (grades 7-12) and their families living in under-resourced and under-served communities in the U.S. and around the globe.
Top Electing Chapters The following chapters were recognized for initiating the most new members in 2008-2009: Princeton, Brown University, Claremont Colleges, Union College, Amherst College, Washington University, Oberlin College, Smith College, Carleton College, Loyola Marymount University, Mount Holyoke College, Denison University, Swarthmore College, Williams College, Lafayette College and McGill-Montreal. •
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Frank Gilmore Elected Treasurer
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lso at the 2009 Sigma Xi Annual Meeting, W. Franklin (Frank) Gilmore
was elected Society treasurer. He is chancellor and the 10th campus CEO of Montana Tech, an institution started 100 years ago as the Montana School of Mines. Prior to coming to Montana Tech, he was the executive vice president and vice president for academic affairs at West Virginia University Institute of Technology. For 26 years he was a professor, chair and research professor in the Department of Medicinal Chemistry at the University of Mississippi. A native of Mississippi, Gilmore earned a B.S. in chemistry at Virginia Military Institute and a Ph.D. in organic chemistry at the Massachusetts Institute of Technology. As a graduate student at MIT, he was elected to full membership in Sigma Xi in 1960. After service in the Army, he spent a postdoctoral year with DeLos DeTar at the Institute of Molecular Biophysics at Florida State University. He also attended law classes at the University of Missouri at Kansas City while working for the Midwest Research Institute and later attended the Institute of Educational Management at Harvard University. He is a charter member of the University of Mississippi Chapter of Sigma Xi and served as chapter president on two occasions. He has served Sigma Xi in many capacities including President (2002-2003), regional director and committee chairs. He is a life member of Sigma Xi and currently a member of the Montana Tech of The University of Montana Chapter. •
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American Scientist Pizza Lunch Talks Now Available Online
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merican Scientist magazine’s Pizza Lunch lectures are now available online as podcasts. The series features compelling talks by scientists to science journalists and science communicators at the Sigma Xi Center in Research Triangle Park, North Carolina. The goal of these informal talks is to expand scientific understanding among people professionally engaged in explaining science to others. In September, American Scientist editors expanded the audience for the talks by posting them as podcasts, along with speakers’ slides when possible, on the magazine’s Web site at www.americanscientist.org. “The American Scientist Pizza Lunch series has been popular among science communicators locally for more than a decade,” says David Schoonmaker, the magazine’s editor. “We are pleased to offer these talks to a much wider audience via the Internet.” The first podcast is of a talk titled “Everything Is Dangerous: A Controversy” by S. Stanley Young, director of bioinformatics at the National Institute of Statistical Sciences. In his presentation, Young critiques statistical analysis by some epidemiologists, especially their multiple testing of data sets obtained from observational studies. A talk called “From Cloning to Stem Cells: How Can Pigs Help Us Solve Problems in Human Medicine?” is by Jorge Piedrahita, professor of genomics at the North Carolina State University College of Veterinary Medicine. He describes his research with cloned swine and how their abnormal growth provides insight into human placental defects, the ways transgenic pigs may help grow human tissue and
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Comment on Energy Crisis White Papers
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s part of its Year of Energy, Sigma Xi invited members and the public to share their energy expertise by submitting white papers that present solutions to some aspect of the energy crisis. We had an excellent response, and all accepted white papers are posted online at http://energy.sigmaxi.org where readers can download, rate and comment on the papers. how pigs could help advance stem cell therapies. The first scheduled talk in the 2009-2010 season was by University of North Carolina at Chapel Hill chemist Thomas J. Meyer, who leads a new research center that this year landed a $17.8-million federal grant to develop solar fuels and nextgeneration photovoltaic technology. The center’s vision is that solar fuels one day could use the sun’s energy to make fuels from water and carbon dioxide for heating, transportation and energy storage. The center also expects that nextgeneration photovoltaics could generate electricity by inexpensive “solar shingles” on the roofs of buildings. In the October lecture, Steven E. Churchill, an associate professor of evolutionary anthropology at Duke University, discussed the prehistoric origins of projectile weapons. Using forensic experiments on pig carcasses, Churchill has gathered evidence that anatomically modern humans may have deployed their projectile weaponry against Neanderthals. The 2009-2010 season of the American Scientist Pizza Lunch series is sponsored by the North Carolina Biotechnology Center. •
There are also several guest blog entries and other energy resources at the site. Below is a list of white papers available online: Renewable and Sustainable Production of Practicable Fuel, J. A. Van Vechten Technology to Reduce Energy Demand in Steel Plants, Saurabh H. Mehta Potential Applications of Hydrogen Generation from Cheap Forms of Aluminum Reacting With Water, Solomon Zaromb and
Joseph R. Stetter Systems Analysis and Recommendations for R&D and Accelerated Deployment of Solar Energy, Kevin DeGroat, Joseph Morabito,
Terry Peterson, and Greg P. Smestad Combined Thin Film Photovoltaic and Reflective 3D Parabolic Panels for UtilityScale Solar Dishes, James C. Townsend and
Francis C. W. Fung Fuels from Municipal Waste, David W. Emerson, Jacimaria R. Batista, Samir F. Moujaes, Thomas A. Nartker, and Spencer M. Steinberg Cradle to Cradle: Turning Nuclear “Waste” Into Nuclear Fuel, Marilyn Waite Where is the Concern for Ecology in the Energy Debate?, Norman D. Meadow,
William H. Biggley and Ajax Eastman Fungi in Bioremediation of Oil Polluted Environments, Omokaro Obire and
Ramesh R. Putheti Renewable Energy: How Much of an Option Is It?, Stan Jakuba •
www.sigmaxi.org
American Scientist
2010 January-February 95
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Science Festival, Affinity Programs and More
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igma Xi has joined more than 200 organizations to participate in the Inaugural USA Science & Engineering Festival. The festival will be the country’s first national science festival and will be held in Washington, D.C., in the fall of 2010. Its mission is to re-invigorate the interest of our nation’s youth in science, technology, engineering and math by offering a multi-cultural, multi-generational and multi-disciplinary celebration of science in the United States. The culmination of the festival will be a two-day expo in the nation’s capital that will give more than 500 science and engineering organizations from all over the country the opportunity to present a hands-on, fun science activity to inspire the next generation of scientists and engineers. Keep an eye out for more information on the Sigma Xi exhibit booth that will be hosted by the District of Columbia Chapter.
Affinity Programs
Automatic Dues Renewal
Sigma Xi offers a number of affinity programs that include stimulating opportunities for travel and reduced rates on auto insurance and car rentals, among other benefits. For example, Sigma Xi Expeditions offers special trips at special prices for Sigma Xi members. Recent destinations have included China, South Africa, Sicily, New Zealand, Nepal and Costa Rica.
Many Sigma Xi members are opting for the convenience of automatic membership renewal. You can now have your annual dues paid automatically every year via credit card or bank draft. An e-mail notification of the dues deduction will be sent to you after your credit card or bank account has been charged.
Sigma Xi Clothing Don’t miss our new collection of Sigma Xi and American Scientist clothing that we have launched in association with ______________ NonprofitWebstores.com. From embroidered polo shirts to a variety of T-shirts with favorite American Scientist covers, our new online store offers a great selection of branded apparel.
Wealth Preservation Over the past 10 months, Sigma Xi has created an online resource center called Wealth Preservation & Philanthropic Planning that provides regular updates on impending changes in the U.S. Tax Code. Our resource partner is Crescendo Interactive. If you are unfamiliar with the projected changes, we encourage you to visit sigmaxi.giftlegacy.com and explore the archive of both the public debate and the private sector analysis. •
Society Directors Elected
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uring the 2009 Sigma Xi Annual Meeting in The Woodlands, Texas, chapter delegates elected members to the Society’s Board of Directors. The following directors of geographic regions and constituency groups will serve three years beginning July 1, 2010.
North Central Region
Canadian/International
Lynn Elfner Ohio State University
Paul Kettler Nordic Chapter
Southwest Region
Comprehensive Colleges & Universities
Carter Tiernan University of Texas at Arlington
Area Groups, Industries, State & Federal Laboratories
Thomas Sasek University of Louisiana at Monroe (Election to fill vacancy; term begins immediately and ends June 30, 2011)
The following associate directors will also serve three years beginning July 1, 2010.
Mid-Atlantic Region
Comprehensive Colleges & Universities
Baccalaureate Colleges
Northeast Region
Regina McClinton Grand Valley State University
Joanne Tillotson SUNY at Purchase
Pamela K. Kerrigan College of Mount Saint Vincent
Kelly Sullivan Tri-Cities, Washington
Geraldine Twitty Howard University
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