Discover Magazine 2016-11

3 Days to Pluto, and on to the Nearest Star?

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SCIENCE FOR THE CURIOUS

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NOVEMBER 2016

Final days of the Ice Age giants p.38

PLUS A Checkmate for Cancer

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Hunt for Missing Moon Data Why You Can't Resist the Office Doughnuts

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Contents NOVEMBER 2016 VOL. 37, NO. 9

Astronaut Alan Bean removes the fuel element of the Lunar Module during the Apollo 12 mission on the moon. See page 68 for related story.

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3 Days to Pluto, and on to the Neares

tar?

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SCIENCE FOR THE CURIOUS

FEATURES

32 Alpha Centauri or Bust The nearest star system is 4.37 light-years away. But an ambitious and innovative new idea — involving lasers and nanospacecraft — could get us there in the next 40 years. BY STEVE NADIS

38 Mammoth Island In the middle of the Bering Sea, off the coast of Alaska, sits an island that was once home to a special population of mammoths. Now, researchers are digging deep to reconstruct the past and unearth the cause of the creatures’ demise.

ON THE COVER

BY JESSICA MARSHALL

3 Days to Pluto, and on to the Nearest Star? p.32

46 Checkmate Most doctors ight cancer from the outside with radiation and chemotherapy. But James Allison is ighting it from the inside by hacking patients’ immune systems. The results are changing the cancer game. BY KENNETH MILLER

Mystery on Mammoth Island p.38 A Checkmate for Cancer p.46 Hunt for Missing Moon Data p.68 Why You Can’t Resist the Office Doughnuts p.28

52 Trailblazers Etched into stone in the Canadian province of Newfoundland are the earliest traces of trails made by a living organism. Those irst steps may have set an evolutionary course that changed everything. BY ROBERT MOOR

Photo of the Milwaukee Public Museum Hebior Mammoth by Bill Zuback/Discover. Background: Vibrant Image Studio/Shutterstock; Starshot illustration by Roen Kelly/Discover

COLUMNS & DEPARTMENTS 6

EDITOR’S NOTE

Making Tracks, Leaving a Trail Although we humans tend to focus on ourselves, other species made their marks on Earth long before us.

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PROJECT APOLLO ARCHIVE/NASA

The tree of life sprouts some new branches, a herpetologist recalls the inspiration for a conservation program that gives frogs a leg up, a grad student calculates a new answer for a classic physics problem, and more.

20 VITAL SIGNS Low Blow A young woman goes to three different hospitals because of severe

abdominal pains. Scans come up short. Could the answer lie in her past? BY TONY DAJER

24 BIG IDEA Brewing Life Scientists are cooking up early-Earth conditions to igure out how life got its start. BY JONATHON KEATS

28 MIND OVER MATTER Siren Song of Food If you’re trying to shed some pounds, take a look around. Your environment is more important than you think. BY TAMAR HASPEL

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ORIGIN STORY

Trading Places Long before the Chinese Silk Road, the Indian Ocean was teeming with seafarers creating a sophisticated trading network. BY ADRIANNE DAGGETT

64 PROGNOSIS he Heart of Mississippi Why are African-Americans more likely to experience heart disease? Doctors are turning to the Magnolia State to ind out. BY JEFF WHEELWRIGHT

68 HISTORY LESSONS he Missing Moon Files Researchers race against the clock as they try to recover long-lost lunar data before it disappears for good. BY JULIA ROSEN

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20 THINGS YOU DIDN’T KNOW ABOUT . . .

Bridges They connect our world, on both large and small scales. The Romans built ones that have stood the test of time. And they can even entertain us, in a sense. BY GEMMA TARLACH

November 2016 DISCOVER

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Discover SCIENCE FOR THE CURIOUS

Editor's Note

®

BECKY LANG Editor In Chief DAN BISHOP Design Director

Making Tracks, Leaving a Trail The track was huge. The creature’s hoof had left troughs in the putty of mud along the trail. This was not from some wandering horse. I bent down and studied the prints left by a moose in the Wyoming foothills. Just a few feet away, the comparatively dainty wedged tracks of a deer were a little crustier, crumblier, older. And leaning down closer to the trail, I could barely make out the faded doggy-like paw prints from a coyote. As a 13-year-old, learning animal tracking — among other biology, ecology and hydrology lessons in the wilderness at the Teton Science School — I remember feeling how small, yet integral, humans are in the history and biology of the planet. We’re a blip among creatures that came before us. Two stories in this issue touch on this concept. We delve into why a mammoth population persisted on a remote island in the Bering Sea (see page 38), surviving for thousands of years longer than other mammoth groups. We’re there as a multidisciplinary team of scientists seeks to solve the mystery of what inally doomed the giant mammals. And we take you to the coast of Newfoundland as one writer follows the fossilized footprints of what are considered the Earth’s earliest nomads (see page 52). It’s stories like these that remind me of the eons of life that have populated this Earth before us. And we’ve got the luxury of being able to delve into the science and interpret that natural history.

EDITORIAL KATHI KUBE Managing Editor GEMMA TARLACH Senior Editor BILL ANDREWS Senior Associate Editor MARK BARNA Associate Editor ERIC BETZ Associate Editor LACY SCHLEY Assistant Editor DAVE LEE Copy Editor ELISA R. NECKAR Copy Editor AMY KLINKHAMMER Editorial Assistant BRIDGET ALEX AAAS Mass Media Fellow Contributing Editors

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The Latest Science News & Notes

MATHEMATICAL BEAUTY These branching columns, seen from below, were conceived by Spanish architect Antoni Gaudí to support the complex vault of his worldfamous La Sagrada Familia Basilica in Barcelona, Spain. Gaudí drew inspiration from natural structures, such as trees, and mathematical concepts, like U-shaped hyperbolas and parabolas. He knew the results would not only look mesmerizing, but also would make for strong arches; they don’t need internal bracing or external buttresses. Gaudí, who worked on the basilica from 1883 until his death in 1926, was among the first to use these equilibrated structures as design elements.  ERNIE MASTROIANNI; PHOTO BY SYLVAIN SONNET/HEMIS/ALAMY

November 2016 DISCOVER

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Tree of Life Bacteria branch out on this updated phylogenetic diagram.

Bacteria Actinomyces odontolyticus: Found in the human mouth; hosts a parasitic CPR bacterium, TM7x, that has such a small genome it cannot synthesize amino acids on its own.

Jillian Banfield never meant to reinvent the tree of life. But after two decades of studying microbial communities, the University Chlamydia: of California, Berkeley, Culprit of a common geomicrobiologist realized sexually that previous iterations of transferred the tree, which shows how infection. organisms are genetically related, neglected vast swaths of life’s Leptospirillum: diversity. Half the Bacterium found in acidic mine drainage; world’s bacteria provides a habitat were missing, for other organisms that can only survive because they the harsh environment can’t be cultured in its biofilm. in the lab. “They depend on other organisms for many basic requirements,” Banfield says. (She and Helicobacter: her colleagues have Organism shown to identified them only cause by piecing together stomach cancer. fragments of their DNA brought in from the wild.) Informed by more than 1,000 newly sequenced types of microbe, Banfield’s new tree reveals the diversity and long lineage of bacteria, which, along with eukaryotes and archaea, represent the three main domains of life. It also reveals how tightly interconnected many organisms are.  JONATHON KEATS

DISCOVERMAGAZINE.COM

Lactobacillus: Probiotic also used to make yogurt and cheese.

E. coli and Salmonella: Causes of food poisoning.

Archaea Salmonella

The genetic tree of life is divided into three domains: Bacteria, Archaea and Eukaryotes. Bacteria and Archaea, while genetically distinct, are both Prokaryotes, single-celled organisms lacking a membrane-bound nucleus. Eukaryotes include plants and animals and have more complex cells with a nucleus and other organelles enclosed in a membrane.

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Staphylococcus: Causes a common hospital-acquired infection.

Methanogens: Archaea that make the potent greenhouse gas methane.

Lokiarchaeota: Recently discovered on the floor of the Arctic Ocean; shows an unprecedented degree of genetic overlap with eukaryotes; may therefore be a descendent of our common ancestor with simple microorganisms.

Branch of bacteria announced only in 2015; represents about half of the domain’s diversity — and a third of the diversity of life on Earth.

Saccharibacteria: Only CPR member that has been successfully grown in isolation in a lab.

Woesebacteria: Named after Carl Woese, who, based on his earlier work, created the first modern tree of life in 1990 by separating life into the three domains.

Bacteria

Archaea

Eucarya

The first genetic tree establishing the three domains.

Carl Woese

Eukaryotes

Deep-sea vents where Lokiarchaeota was found.

CLOCKWISE FROM TOP: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES; RON SUMNERS/DREAMSTIME; TOMONORI KINDAICHI ET AL./FEMS MICROBIOLOGY ECOLOGY, 2016, VOL. 92, NO. 6; ALISON MACKEY/DISCOVER; CARL R. WOESE INSTITUTE FOR GENOMIC BIOLOGY/UNIVERSITY OF ILLINOIS; CENTRE FOR GEOBIOLOGY (UNIVERSITY OF BERGEN, NORWAY) BY R.B. PEDERSEN; CDC/BETTE JENSEN; CDC/JANICE CARR; TREE OF LIFE: LAURA HUG AND JILLIAN BANFIELD. RIGHT COLUMN FROM TOP: NASA, ESA, J. HESTER, A. LOLL (ASU); PROJECT APOLLO ARCHIVE/NASA

Candidate Phyla Radiation (CPR):

A nearby star went supernova in the year 1054 and created the Crab Nebula. But even closer supernovas could have changed history entirely.

Supernovas Close to Home The death throes of nearby stars might have influenced evolution on Earth. Humans have observed supernovas — the violent explosions that herald death for massive stars — for millennia. Now, using precise chemical measurements of seafloor rock and moon samples, scientists have shown that nearby supernovas rained down radioactive iron and potentially influenced life on Earth. Anton Wallner of the Australian National University led a team that measured 60Fe — a kind of iron ejected by supernovas — in sediment and rock samples from the bottom of the Indian, Pacific and Atlantic oceans. The team found that 60Fe levels spiked some 40 times higher in seafloor material that was roughly 2 million years old, with another significant rise 7 million years ago. The researchers suspect each iron spike happened when the fallout from a supernova explosion hit Earth. Another team of researchers led by Leticia Fimiani of the Technical University of Munich also found 60Fe in lunar soil samples collected by Apollo astronauts. Fimiani’s team suggests that the iron isotopes originated from the same supernova events. Both supernovas occurred beyond the maximum distance, roughly 25 light-years, for a supernova to have catastrophic effects on life on Earth. However, even these distant explosions might have ionized the planet’s atmosphere and produced an uptick in the frequency of lightning. Similar supernovas almost certainly hit the early Earth. Lightning from these events might have assembled new chemical compounds from the atoms and molecules already present Alan Bean and Pete Conrad in the atmosphere, altering evolution. (reflected in visor) collect  KATHERINE KORNEI

samples during Apollo 12.

November 2016 DISCOVER

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ReDISCOV ER W he

BUDreD’s Y? BY JEFF

Buddy Lost and Found As a lonely wolverine approaches his maximum life expectancy, this could be his last winter.

WHEELWR

IGHT ILLUST RATION

BY ERIC

Tracking a wolverine lost odyssey on his through

grazing were curtailed, Canada. wolverines Perhaps stole down 300 live Wyoming from and the Casca today in Mont ana, Idaho ton. The de range young male and in northern surprise, that Washingbut the distan reached Califo rnia was Scientists ce he travele have d isn’t unhea a big radio transm captured wolve rd of. rines and itters attach let them revealed go with beeline migra ed. This kind of tracki males movin tions of ng has hundreds g farther of miles covering and faster with 20 miles than female in a day. s, often Young male wolverines — often typically older males leave their kick them females set birthplaces out up verine, testos shop close to home. — while young terone spikin A 2-year where the -old male g in his blood females are, wol, does not he’s lucky, but he takes he his best shot know two or three. lands in a territo Robert Inman ry where he can and if mate with , a resear cher for the Wildli fe

Sometime OCK the Americ in 2008 a young male the moun an West. tains of wolverine Idaho. No went west left his home one and then south, keepin saw him go. He proba in powering the agenc over obstac y was g bly a major les, as wolve to the highest groun listing should in the process river, of determ rines tend d and be inaliz ining if the smooth sailingthe Snake, and a analysis, ed. Accor major highw to do. He forded issued last federal ding to the through Traversing year, the ay, its curren the empti agency’s wolverine a t habitat ness of easter I-84, then had may lose by the middl near Truck distance of 500 miles, predicted n Oregon. a third of ee, Calif., that reduce e of the centur in the centra he inally reache had been dennin d snowpacks y. The agenc g; that d a forest decad l Sierra Nevad y more isolate home ranges would would hurt female As the larges es since a wolverine a s’ d spaces roamed these range. It be presse t terrest (weasel) retreating as anima d into tighte woods. family, wolve rial members of ls moved snow; that r, the Muste higher with peaks, but rines are physiologica warmer tempe lidae creatures especially l stress. ratures would the of snow, of snow. ball bodies Of cold course Their thickl cause are perfec and , y furred, blizzards. tly constr snowpacks, long before climat bowlingucted to Their e change unbridled retain legs, let them paws, seemingly threatened most wolve trapping too big for heat during the and poison rines from bound over through. their stubby on in the ing had driven the contin the snowp Snifing a northern ental U.S. ack witho dead deer Rockies, a wolverine Colorado, buried benea ut breaking but the thin Wolverines hung bores down Michigan, th an avalan throttle. populations gone by Minnesota like a tunne (Wolverines the middl che, in ling machi e of the 20th and the North are was alive.) southernmo ne on full east were Since female scavengers, eating century. st group, Wolverines late in winter anything by a chang s bear their those in that once the Sierra in the e in time, the young in maintain Nevad sites they sheep. Biolog their food supply snow chamb their snow select for — deer, elk a, were hurt ers ists think denning cover long by livesto In short, those anima and have to into spring ck grazin no snow, ls were pushe bighorn g in the no wolve change’s to protec Sierra. When rines. On threat t the kits. winter came high summer meado d out the basis Service found to snow levels, to lower of climat ws of the and the the U.S. range, little wolverines e Fish and species in carrion remai livestock were herded Although warranted Wildlife the contin a furtive ned for wolve listing as ental U.S. few 1930s, a threatened rines. the last conir probably surviv in 2010. As of this ed throug med Sierra specimen January, h the in 1922. wolverine 46 was shot But over as a the past 50 years, as trappi ng and high-e levation HANC

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Eight years ago, a young male wolverine from Idaho surprisingly showed up near Truckee in California’s Sierra Nevada range. Wolverines had been absent there for 80 years. Discover profiled the animal in March 2014, in the article “Where’s Buddy?” “Buddy” was the nickname given by wildlife biologist Amanda Shufelberger, who works for Sierra Pacific Industries, a lumber company. Young wolverines migrate to empty territories to find mates and start new populations. Buddy set up shop on a snowy mountaintop owned by the timber company. It turned into an odd kind of love triangle. Each winter, Shufelberger kept tabs on Buddy with motion-sensitive trail cameras, which she set near trees baited with raw chicken. She never saw him during the summer or, for that matter, in the flesh. Also, she never recorded a female wolverine. The media ran stories about “the lonely wolverine.” People DISCOVERMAGAZINE.COM

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felt sorry for Buddy. He grew middle-aged, then old. Each winter, when she’d bait her cameras, Shufelberger feared she might not see Buddy again. After all, why would he stick around? Besides, as a predator living near humans, he risked being injured, poisoned, trapped or shot. She spotted him as usual in February 2015. Then a whole year passed. Last March, to Shufelberger’s relief, her camera caught him once again as he snuffled about his “magic chicken tree.” Buddy was now approaching 10 years old, an age most wolverines never reach. “I hope there’s a female,” Shufelberger says. “Is she just shy and not coming on camera?” Most likely there isn’t a hidden female. “We’re getting to the point where I won’t expect to see him next winter,” she says.  JEFF WHEELWRIGHT

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California’s lonely wolverine was caught on camera last winter.

Do you know what this is? Pop over to page 18 for the answer.

TED KINSMAN/SCIENCE SOURCE

W H AT THE...?

November 2016 DISCOVER

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The Lazarus Frog A small frog in a dark rainforest gives one scientist hope for endangered amphibians. Jonathan Kolby knows extinction is final. The James Cook University herpetologist studies global frog populations and their decline from the widespread and deadly chytrid fungus. Now Kolby hopes to give endangered frog populations a leg up by allowing them to develop natural resistance against chytrid in temporary captivity. An unusual brown frog in Honduras’ Cusuco National Park inspired his approach. He first spotted it while surveying amphibians with students back in 2007.

Researcher Jonathan Kolby goes vertical at Cusuco National Park in search of tree frogs.

IN HIS OW N WOR DS

Jonathan Kolby’s discovery image of Craugastor milesi, the Miles’ Robber Frog, showed this amphibian wasn’t all the way gone.

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It was Craugastor milesi, the Miles’ Robber Frog. At that time, only two species of frogs had been declared extinct in Honduras, and this was one of them. It was an amazing moment. I study amphibian chytrid fungus, and this was one of the species we believe has disappeared likely because of this disease back in the ’80s as it swept through Central America. Five years later in 2013, I found a second one. This was on the other side of the park. Something caught the corner of my eye. I knew there was a frog watching me. I started staring at this big muddy puddle, waiting for another movement. Then I saw the little nose come above and look at me. It was another Miles’ Robber Frog, miles away from the last one. Neither one tested positive for chytrid, although I know it’s highly prevalent throughout this park. There may have been a very dramatic population crash when this disease swept through, but some animals were hanging on. There’s still hope. It’s exciting for me because I’m establishing the Honduras Amphibian

Rescue and Conservation Center. If we keep these species alive in the wild over many, many years, by captive breeding and reintroduction and head-starting, we could have these strong survivors begin to come back and repopulate the environment.  AS TOLD TO ASHLEY BRAUN

Frog rescue labs went up in the summer at the Honduras Amphibian Rescue and Conservation Center.

CLOCKWISE FROM TOP: KATIE GARRETT; JONATHAN KOLBY (3)

It was about 10:30 or 11 at night. Everyone was getting a little tired. We were about to head back, and I saw a frog. It was this little brown frog, pretty nondescript. I jumped into the mud and totally missed it. For the next half-hour, I proceeded to crawl around in the river. Eventually I gave up. It was gone. In 2008, I had one chance to get back to this same location. I couldn’t believe my eyes when I got there. On that very same rock was a little brown frog. I thought I was hallucinating. I dove down and caught it.

When Mars Tipped Over How a bulge of volcanoes shaped the Red Planet.

TOP: ESA/DLR/FU BERLIN/JUSTIN COWART. BOTTOM: SYLVAIN BOULET ET AL./MACMILLAN PUBLISHERS LTD/NATURE/VOL 531, MARCH 17, 2016

For hundreds of millions of years, lava bubbled up from the depths of Mars, forming a staggering volcano system called the Tharsis Bulge. Its four major volcanoes near the equator — including Olympus Mons, the solar system’s largest — are all taller than Mount Everest. And now, new research reveals that the bulge’s massive size had serious consequences for the Red Planet. According to a French-led team, the bulge made Mars tip over some 3 billion years ago. Its outer layers, the crust and mantle, rotated until the enormous volcanoes traveled about 20 degrees, from the polar regions down toward the equator. The research, published in Nature, rewrites the first billion years of Martian history. The team’s climate modeling contradicts existing theory by showing that the river valleys seen on Mars could’ve flowed while Tharsis was still forming, instead of emerging afterward. And the eruption of waterrich gases would’ve helped fuel Mars’

Four massive volcanoes make up the Tharsis Bulge on Mars. The largest of the four, Olympus Mons, is at bottom right.

early atmosphere for a while, driving precipitation on a wet planet. But by the time the Tharsis volcanoes let out their final breath, the heat was gone, and the planet was abandoned to an endless, dry winter — a world not too different from what we see today.  ERIC BETZ

Valley Networks

Tharsis

20º TPW Tharsis

New research indicates that the load of Mars’ Tharsis bulge caused the planet’s outer layers to rotate. As a result, the planet’s axis reoriented — a phenomenon called true polar wander (TPW) — and tipped about 20 degrees, as this image shows. (Warmer colors denote higher elevations.)

DID YOU Death isn’t the end — at least for some genes. Postmortem studies conducted on mice and KNOW? zebrafish by geneticists at the University of Washington revealed that hundreds of the animals’ genes remain active, continuing to synthesize molecules and perform other tasks, up to 96 hours after the animals’ death.

November 2016 DISCOVER

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Around a Strange Sun

Habitable Zone

Explore the alien landscape of Earth’s nearest neighbor.

To calculate where liquid surface water can exist, astronomers combine a star’s heat with the sunlight reaching a planet’s surface. But even a Goldilocks-perfect orbit is no guarantee of life. Mars is in our sun’s habitable zone and was left barren without an atmosphere.

After decades of failed searches, astronomers from the Pale Red Dot project found a planet around our nearest star, Proxima Centauri. This world, Proxima b, is roughly Earth-sized and nestled in its star’s habitable zone — the region where oceans can exist. But that’s about where the similarities end. Proxima Centauri is a cool, tiny red dwarf star. To stay warm, Proxima b’s orbit is tighter than Mercury’s.  ERIC BETZ

Habitable zone

Mercury’s orbit

Proxima Centauri

Sun

Darkness and Light

Proxima b orbit

Proxima b’s close-in orbit may mean the planet is tidally locked, with one side stuck in sunlight, the other in eternal night. If so, life’s best chance is in the twilight between the two, bathed in a kind of everlasting sunset.

By the Numbers 11. 2

The number of Earth days it takes Proxima b to orbit its sun — that’s a short year!

1.3 The minimum mass of the newly discovered planet, compared with Earth. 4.6 million

Distance (in miles) from Proxima b to Proxima Centauri. Compare that with 93 million miles from Earth to the sun.

SOURCE: NATURE; DOI:10.1038/NATURE19106

Proxima b’s radius might be 10% larger than Earth’s, assuming a rocky composition.

Uranus

Saturn Habitable zone Earth Jupiter

Mars

Mars

Neptune

Earth Mercury Venus

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Proxima b (artistic representation)

Red Dwarfs Everywhere

A Drab Planet

Sun

Proxima Centauri

as it appears in Earth’s sky

as it appears in Proxima b’s sky

Sunset on Earth

If Earth orbited a red dwarf star, its light would make our pale blue dot take on more of a drab, greenish-yellow tone.

Earth around the sun

Earth around a red dwarf

Sunset on Proxima b

Sun

Actual size difference

Proxima b hugs tight to its tiny red dwarf star. So sunsets would look redder and darker, with the sun appearing three times larger than our own. Stranger still: If one side of Proxima b forever faces its star, the sun would never set.

£

LARGE ORBIT DIAGRAM: ALISON MACKEY/DISCOVER AFTER ESO/M. KORNMESSER/G. COLEMAN. SOLAR SYSTEM DIAGRAM: ROEN KELLY/DISCOVER. EARTH, PROXIMA B, PROXIMA CENTAURI: PHL@UPR ARECIBO/NASA EPIC TEAM. SUNSETS: PHL@UPR ARECIBO. SUN: SDO

If the Milky Way had just 100 stars — it’s more like 100 billion — 75 would be red dwarfs. Finding a roughly Earth-sized world in the habitable zone next door means those other small suns might harbor similar planets.

ON THE WEB

Readers respond Proxima b is the nearest exoplanet we’ll ever find. When news hit the web, Discover readers were pumped, to say the least.

“Why go there at all?

Just build a giant kick-ass telescope and look at it.”

— Brian Hurren

“This is as good as it gets, in our own backyard!” — Joanna Leigh

“Although very interesting . . . I believe it will be uninhabitable. Nice dream, though. We should continue trying to find a habitable planet that parallels our own.” — Sharlyn

Proxima Centauri

“Very promising. It would take technology we haven’t invented yet, but it is at least theoretically possible that we could send an unmanned probe to Proxima b.”— Erik Bosma

“Hopefully there is intelligent life on this new planet. They must have it somewhere.” — Michael

Sending an unmanned probe to Proxima b may happen sooner than you think. Read about it on page 32.

November 2016 DISCOVER

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THE

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SCIENCE SM ACK DOW N

Journey Through the Center of the Earth A student calculates a more realistic answer to a classic physics homework problem. Imagine drilling a hole through Earth, hopping on a train powered by gravity alone and traveling through from one end to the other. How long would you spend on that “gravity train” before popping out on the other side? It’s a question physics professors have been asking students for decades, and they always expect the same answer: 42 minutes, 12 seconds. One graduate student claims to have shaved a few minutes off that traditional travel time. In Science Smackdown, we let a prof and the grad student duke it out.  SARAH SCOLES

Alex Klotz, a doctoral student at the time and now a postdoctoral researcher at MIT, doesn’t buy that answer. “I remember just looking at a graph of what the inside of the Earth is like in terms of density and trying to figure out how that would affect the time it takes to fall,” he says. The crust, where we live, is much less dense than the mantle below, which is less dense than the core. When he considered Earth’s true Mantle composition, and the varying accelerations this composition Core created, Klotz found the train’s trip takes just 38 minutes. But, more interestingly, he could also get this new result by ditching density and making his own simplification: Gravity stays

Researcher Alex Klotz reimagined the calculation for this classic problem, altering assumptions about gravity and density.

constant the whole trip. It works because gravity doesn’t change drastically until the train gets halfway to the core. At that point, the contraption is moving so fast that the seconds spent near the center hardly matter. So by this reasoning, Klotz says, the gravity train needs an updated schedule.

DID YOU If you’ve said, “I do,” your heart owes you. Researchers from the University of East Anglia KNOW? found that individuals who are married are up to 14 percent less likely to have a fatal heart attack. Marriage is also associated with a reduced number of hospital stays in general.

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FROM TOP: OMER MEI-DAN; GABRIEL KOCHER; ROEN KELLY/DISCOVER; BENGUHAN/SHUTTERSTOCK

Deceleration

In 1966, physicist Paul Cooper calculated how long the train would spend falling from one side of Earth to the other. People have been thinking about this hypothetical scenario — pondering the motion of mass inside Earth — since Robert Hooke first proposed an earlier, pre-train version of it to Isaac Newton in the 17th century, says Purdue University mathematician Alexandre Eremenko. The traditional solution, based on Cooper’s calculation, simplifies things by pretending Earth is equally dense from crust to core. At the beginning of the ride, gravity is strongest, speeding the train along. As the train descends, gravity will decrease by the same amount for every mile the train falls. At the halfway point at the core, gravity is lowest and begins to act as a brake, slowing the train as it approaches the destination.

Gravity Is the Same All the Way Through

Acceleration

Earth’s Density Is Equal All the Way Through

If Mexico’s Cave of the Swallows cut through Earth, classic physics says that if you dove in, it would take about 42 minutes to pop out the other end. A new approach shortens that trip.

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INBOX Questioning a Star’s Stability A letter to Yvette Cendes, author of “The Weirdest Star in the Universe,” from the July/August issue: As an amateur astronomer, to me the weirdest thing in the article was that a red giant star could envelop a neutron star and continue to exist as a Thorne-Žytkow object (TZO). It would seem to me (I’m not a physicist) that the neutron star, being surrounded by the red giant and as it approached the higher-density center, would rapidly collect enough mass to explode as a supernova or collapse as a black hole. These situations are mentioned as possibilities, but to my simplistic mind, they would be almost certain probabilities within less than “a few thousand (or a million) years.” Perhaps the explanation suggested for the X-ray source 1E161348-5055 is the answer, but it still perplexes me that the system could remain for so long. Could the neutron star’s slow rotation be explained partially by the accretion of mass, emitting X-rays and blowing gaseous mass away, slowing the inevitable event but approaching the critical value for destruction? What do the experts say about this? Ed Jones Friendswood, TX

Wake-Up Call A response to “Everything Worth Knowing: Antibiotic Resistance,” in the July/August 2016 issue: I was unaware and startled by how readily bacteria can become resistant to our antibiotics . . . scary! The amount of antibiotics consumed in the U.S. alone — 7.7 million pounds by people and an additional 29.9 million pounds consumed by farm animals, in 2011 — is astounding. M. Oxford Addison, TX

A high-speed strobe froze the brief, 1/20,000-of-a-second moment of this balloon bursting. The balloon contained a few milliliters of water that turned into vapor during inflation. When the balloon popped, the air inside expanded, cooled and turned the vapor into water droplets inside the balloon’s ragged remains. (See close-up on page 11.)

TED KINSMAN/SCIENCE SOURCE

W H AT THE...?

Yvette Cendes responds: The short answer is no one knows for sure, and how a TZO remains stable is an open area of debate. The current theory is neutrinos are involved — we know they’re responsible for a lot of cooling in “normal” neutron stars. However, others argue neutrino cooling is not sufficient, and some sort of explosion should occur. Ultimately, though, a lot of TZO theory was a bit older when the discovery of the candidate TZO was made, and needs to be updated to explain the details. Sorry I can’t give you a definitive answer — I wish I had one. But if it’s any consolation, lots of experts wish they had one, too.

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Physicist Winkless ofers an easyreading crash course on the engineering and dayto-day operations of our urban centers, and previews what the cities of the future might be like.

More than half of American THE LION IN households have at least one THE LIVING cat or dog, but rarely do we reROOM ally appreciate these furry friends How House Cats as evolutionary masterpieces. Tamed Us and Took Horowitz, who runs Barnard Over the World College’s Dog Cognition Lab in By Abigail Tucker THE New York, focuses on the developALIENS ment and potential of dogs’ most ARE sense: scent. Take a black COMING! impressive Lab mix, for example, that helps The Extramarine biologists collect orca scat ordinary in Puget Sound by sniffing it out Science up to a nautical mile away. In Lion, Behind Our journalist Tucker pulls together the Search for latest research into how and why Life in the cats allowed us to domesticate Universe them. She also explores the By Ben Miller sometimes-disturbing conseIt’s a great big quences of that relationship, universe, and odds from controversial feral are we’re not alone cat colony programs to BEING A DOG in it. An actor and enthusiasts who create Following the comedian armed with new breeds based Dog into a a degree in quantum on deleterious World of Smell physics, Miller makes mutations. By Alexandra a solid case for the Horowitz existence of extraterrestrials. Whether it’s an objective look at UFO encounters, detailing the chalMURDER AND THE MAKING lenges of contacting OF ENGLISH CSI aliens or explaining By Ian Burney and Neil Pemberton how life on Earth can inform our search, his History bufs and forensic nerds alike snappy, conversational style will keep you will delight as science historians turning the pages.

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Pemberton and Burney present a thoughtful analysis of the key players and events that helped crime scene investigation in Britain develop into what it is today.

November 2016 DISCOVER

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Vital Signs

Low Blow Severe belly pain lands a young woman in the hospital not once but three times — yet abdominal scans find nothing. BY TONY DAJER

→

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Overnight, her sodium had tanked from borderline-low to very abnormal. I noticed the scar on the right side of her neck. “That’s where they inserted the central venous line,” the husband explained. “At the irst hospital, to give her concentrated saline solution.” “That’s unusual,” I said, not quite believing him. “Her blood sodium level was very low.” “Did they make a diagnosis?” I asked. Healthy young women don’t see a drop in their blood sodium levels for no reason. “They weren’t sure. But they got it back up.” “We’ll start some pain medication right now,” I said, wrapping up my exam. Her abdomen was tender everywhere. Dilaudid — hydromorphone — is 10 times more potent than morphine, and the top pick among drug-seekers. But it’s what she needed. We were the third hospital she had visited in the three weeks since the pain started. I perused the records our ER had

gathered the day before. At that irst hospital, her sodium level had been critically low, and they kept her a full week; the husband was spot on. After a slew of other tests, they discharged her with oxycodone, a potent oral narcotic. The pain’s origin remained mysterious. Five days later, it surged back. At hospital No. 2, the sodium was also low. During an equally fruitless work-up, more salt and Dilaudid was pumped in. They released her — diagnosis still unknown — three days later. And then she came to us.

WHEN SODIUM TANKS My colleague Louis, compact and engineer-precise, sat down next to me. “I saw her yesterday,” he said. “You think she’s drug-seeking?” I asked, although my own gut feeling at this point said no. “The abdominal scan was negative, so we went with functional pain. Lots of people have abdominal pain we never explain. I’m guessing there’s more, though,” Louis said evenly. “Their doc saw her today and sent her back,” I told him. An hour later, her lab results came up. Overnight, her sodium had tanked from borderline-low to very abnormal. Louis glanced at the screen.

9NONG/SHUTTERSTOCK

“She’s back.” Jackie, our seen-it-all triage nurse, gave me the look. A wave of moaning, a basso profundo, found my body’s frequency and set it vibrating. The source, a 28-year-old woman, lay on the ambulance gurney, clutching her belly. The rumble illed the space around her. The husband, gamely standing by her side, quickly answered the registrar’s questions. Jackie illed me in. “Belly pain. Lots of Dilaudid [an opioid pain medication] last night. Abdominal CT negative.” She raised her eyebrows. “Good luck.” The patient had landed in our hospital the day before in extreme pain, and here she was again. Uppermost in my mind was that 15,000 Americans died last year from narcotic overdoses — most originally hooked by a doctor’s prescription. Ten minutes later, I stood at the foot of her bed and asked, somewhat inanely, “Where does it hurt?” Her hands still cupped gingerly over her abdomen, my patient kept moaning. “You had several doses of Dilaudid last night, no?” I asked. “It helped for a while,” the husband said. “But today it came back hard. Our family doctor did an internal exam and thinks there may be an appendicitis the scan missed.” The eyes swayed me. Her lids were half-closed, her gaze remote, as if the outside world lay far beyond the horizon of her pain. “Oooooh,” she rumbled, dropping an octave.

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Vital Signs

A CLOGGED-UP FACTORY Hemoglobin, the oxygen-carrying essence of blood, is a shape-shifting agglomeration of four heme molecules and four proteins (globins). Heme holds the iron that binds oxygen, which, in turn, colors it scarlet. Protein To make heme, (globin) Hemoglobin eight enzymes work along a molecular conveyor belt. It’s a tightly coupled process, and problems can arise if any Iron enzyme malfunctions bound or gets overwhelmed. to heme Then, partially processed molecules can back up at that enzyme’s station like Red blood cell Model Ts waiting for their wheels. Worse, the absence of inished product at the far end can rev up enzymes at the front to crank out even more half-inished components. Porphyria is the family name for diseases of faulty heme production. Damage any of the eight enzymes, and you get a different type of porphyria. The flaw usually lies in a mutated gene for one of the two copies of the enzyme — which reduces, but does not cancel,

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overall production of heme. Derived from the Greek word for purple, the term porphyria stems from the red or brown color that patients’ urine can turn during an acute attack. Unfortunately, those uninished heme precursors are toxic, especially to nerve cells. Four of the porphyrias are classiied as acute. They attack nerves throughout the body in muscle, skin, brain, intestines and even the heart. The remaining porphyrias are mainly dermatologic, causing rashes. Acute intermittent porphyria (AIP), the most common acute porphyria, affects 1 in 20,000 people. It stems from a defect in the conveyor belt’s third enzyme. Although abdominal pain is its hallmark, it can also provoke anything from psychosis to rapid pulse to anxiety to muscle weakness to chest pain to constipation. The mutation may not cause disease in every carrier, leading to “skips” in the family history. With one good gene and one bad, a functional-enough No. 3 enzyme can handle its share on the conveyor belt until a stressor hits, or related enzyme systems overload. Triggers of acute attacks include carbohydrate starvation (which kick-starts the irst enzyme on the conveyor belt), as well as alcohol, stress and dozens of drugs. Intriguingly, the Atkins diet — all protein, no carbs — caused a raft of new AIP cases. The “intermittent” of AIP doesn’t begin to describe it. The scattershot symptoms are confusing enough, but the syndrome’s timing is downright ridiculous. A patient’s irst attack may not hit until well into his or her 30s. The next may not come for years. Worse, the episodes may not even resemble each other: Last year’s anxiety attack and fast heartbeat might share nothing with this year’s abdominal pain and low sodium. Hyponatremia is thought to stem from toxic effects on the hypothalamus, the central area of the brain that regulates water and salt excretion.

Timely diagnosis isn’t just about pain relief; unchecked, AIP can cause permanent neurological damage or death.

A STRONG CLUE We asked again. “Are you sure no one in your family had an illness, odd attacks, that came and went?” Through her fog of pain, our patient perked up. “Oh. My mother. When she was a teenager, something attacked her nerves and blood vessels.” “Where’s your mother-in-law?” I asked the husband. “Overseas,” he replied. “Call her,” I urged. “Ask if she’s heard the term porphyria.” A few minutes later, he came running over. “Yes.” “Holy cow!” I yelled. Louis ordered the diagnostic test: urinary porphobilinogen (PBG). The result would take a day or two. The deinitive treatment for three of the four acute porphyrias is intravenous hemin — the assembly line’s end product — to shut down runaway production. For starters, we admitted the patient to the intensive care unit to treat the low sodium. The strongly positive PBG came back the next day. She received glucose and a full course of hemin. Complete recovery took a slogging 10 days. I called the ER directors at hospitals 1 and 2 with the diagnosis. Great teaching case, I told them, but wrapped inside that statement was the question: How do you pass up a clue like that ultra-low sodium level? In the end, what most puzzled me was, if the mom knew, and the daughter sort of knew, why hadn’t the porphyria clue popped right up? Maybe, Sherlock, it’s how you ask the question. D Tony Dajer is director of the emergency department at New York-Presbyterian/Lower Manhattan Hospital. The cases described in Vital Signs are real, but names and certain details have been changed.

TIMONINA/SHUTTERSTOCK

“OK, let’s think syndromes.” He logged on to the clinical research website UpToDate.com. “Recurrent abdominal pain? How about porphyria?” he said, ingering the keyboard. “Why not?” I smiled, thinking an answer of “unicorn” was about as likely. He pulled up the page. We read together. “Abdominal pain is the most common symptom. Associated indings include hyponatremia [low sodium].” “Huh,” I said. “I didn’t know that.” “Neither did I,” Louis admitted. “Porphyria?” I said, incredulous. “But it’s inherited. You got the family history yesterday, right?” “Twice. Me and the surgery consult. An aunt had brain cancer. That’s all.”

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Big Idea

Brewing Life Lab-grown comets and hydrothermal vents are helping scientists unravel life’s strange origins on a young, sterile Earth. BY JONATHON KEATS

In Jeffrey Bada’s laboratory at the University of California, San Diego, there’s a cardboard box containing the earliest evidence of how life began on Earth. The box holds hundreds of tiny vials illed with grimy, brown residues collected in the early 1950s by a University of Chicago graduate student named Stanley Miller. Each vial is marked with a page number corresponding to a notebook where Miller recorded an experiment undertaken with his adviser, the Nobel Prize-winning chemist Harold Urey. Their goal was to synthesize amino acids — the building blocks of life — as they might have been created on early Earth. The results launched a hunt for life’s origins that’s now uncovering these building blocks in surprising places, like the surface of comets and in deep-sea hydrothermal vents.

A LABORATORY EARTH The modern origin question has bedeviled scientists since Charles Darwin proposed his theory of evolution in the 19th century. If all modern species evolved from earlier life-forms, the branching must have begun with some common ancestor. Darwin speculated that our microbial Eve arose from a “warm little pond with all sorts of ammonia and phosphoric salts.” Eight decades later, Urey sought to be more precise. He enlisted research on early planetary conditions to show how interactions

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heir goal was to synthesize amino acids  the building blocks of life  as they might have been created on early Earth. between the atmosphere and oceans might have produced an organic “primordial soup.” Inspired by a 1953 lecture in which Urey outlined his ideas, Miller proposed to cook up the soup in a lab. Urey was skeptical. At 23 years old, Miller had scant experience as an experimentalist. Urey gave him one year and a budget of under $1,000. Miller instructed the campus glass

blower to make an apparatus with two interconnected chambers, one representing the ocean and the other standing in for the atmosphere. During the experiment, a flame boiled the ocean water, simulating evaporation. The steam traveled through a tube into the atmospheric flask, which contained hydrogen, methane and ammonia. An electric spark simulated lightning. A second glass tube condensed the vapor, making the humid atmosphere rain back down into the ocean. Within less than a week, the clear liquid darkened. Miller analyzed the brew and found ive amino acids, which are the organic constituents of proteins. Published in the May 15, 1953, issue of Science, the results galvanized scientists and generated global headlines. The New York Times credited Miller and Urey with inventing

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“a laboratory Earth.” Time dubbed the experiment “semi-creation.” And it turns out that Miller underreported the richness of his prebiotic soup. When Bada’s lab inherited the leftover residues after Miller’s death in 2007, Bada examined them using modern instruments. He detected more than eight times the number of amino acids found by Miller. The surprising success of the MillerUrey experiment has made it a classic in many textbooks, but there was also a problem at its core — namely, Urey’s hypothesis that the early atmosphere was flush with methane and ammonia. “In fact, it was carbon dioxide with nitrogen, or carbon dioxide with a little methane,” Bada says. Miller knew about the problem, and when he replicated his experiments in the 1980s using a more plausible mix of gases, most turned up no amino acids.

A 23-year-old Stanley Miller (top) poses with his life-brewing contraption. Decades later, Scripps researcher Jeffrey Bada (middle) made his own primordial soup experiments. He also re-examined Miller’s original samples (bottom).

SEEDING AN RNA WORLD About a decade after Miller’s unsuccessful second attempt, the European Space Agency added a young German chemist named Uwe Meierhenrich to its Rosetta

mission to Comet 67P/Churyumov– Gerasimenko. Meierhenrich helped develop instruments that allowed the Philae lander to probe the comet’s surface for organics. But to test Philae’s abilities, he’d need a comet on Earth.

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Meierhenrich found what he needed at Leiden University in the Netherlands, where astrochemists were making artiicial cometary ice to test how these dirty snowballs form. Their technique was akin to Miller’s simulated primordial soup. The Leiden scientists replicated the frigid vacuum of interstellar space, then introduced the chemicals found in cometary ice and hit them with ultraviolet light like that emitted by stars. This process produced mere micrograms of comet, but it was enough to test Rosetta’s instruments. The equipment worked impeccably — and detected 16 amino acids. Although researchers suspected they’d see amino acids on 67P — having already detected them in certain primitive meteorites — nobody expected that the organics would form instantaneously in a simple ice analog on Earth. As doubt grew over the Miller-Urey experiment, Meierhenrich’s research lent strong support to an alternative hypothesis: that the organic ingredients of life came from outer space. And support for a cometary origin has only grown since Meierhenrich published his initial results in 2002. Twelve years later, the Philae lander descended onto 67P and detected organics that matched the ice from Leiden. Earlier this year, Meierhenrich’s lab at the University of Nice Sophia Antipolis reported another major advance in Science. Analyzing ice analogs with a new technique called multidimensional gas chromatography, they detected the chemical ribose — no ordinary organic. The complex sugar is the chemical backbone of RNA, which is widely acknowledged as the genetic regulator of life before DNA. Many researchers even theorize an “RNA world” that predates our own. These molecules would have evolved into the irst living organisms. Ribose is also dificult to produce. Living cells do it well, but the principal

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Comet 67P (top) holds many building blocks for life. German chemist Uwe Meierhenrich made similar ingredients in a laboratory comet.

inorganic process for making complex sugars is called the formose reaction. It requires careful lab preparation of concentrated formaldehyde. Meierhenrich thinks that a similar reaction naturally takes place in interstellar space — without the fussy chemistry. “You see this in cometary ice,” he says. “You do not see this on the surface of early Earth.”

CHEMICAL GARDENS However scientists do see the formose reaction in at least one terrestrial environment. In 2011, researchers at the Max Planck Institute of Colloids and Interfaces synthesized ribose

in conditions simulating a hydrothermal vent. Alkaline hydrothermal vents are found on the seafloor near where tectonic plates meet. Hot water seeps up from beneath the Earth’s crust, transporting a rich mix of minerals that provide chemical sustenance to communities of microbes. Explorers irst saw a cluster of these white chimneys near the Mid-Atlantic Ridge in the early 2000s. Ever since, researchers have theorized that such vents could have nurtured the earliest life on Earth. “You have a kind of one-stop shopping,” observes Linda McGown, a chemical biologist at Rensselaer Polytechnic Institute. The vents provide the energy source, raw materials and environment for chemicals to concentrate and reactions to take place. McGown’s lab is testing this idea by growing mineral chimneys in glass vessels and seeding them with organics. Last year, her team showed that vent-dwelling ribonucleotides — molecular RNA precursors — can form into short chains of RNA. Placing her “chemical gardens” under

high pressure, to simulate conditions on the ocean floor, only improves the eficiency of RNA formation. And while McGown’s bench-top experiment required lab prep of the chimneys’ raw materials to obtain RNA linkages, her newest research shows that unprepared minerals will do the trick in pressurized conditions. Nevertheless, McGown refuses to conclude that Darwin’s “warm little pond” must have actually been a hot hydrothermal vent. Given ongoing uncertainty about early Earth conditions, she believes in keeping an open mind. Her pragmatism is shared by Carnegie Institution mineralogist Robert Hazen, one of the most widely respected researchers in the study of life’s origins. Instead of seeing alternate theories as competitive, he contends that “the organic molecules come from many sources.” Space and Earth both contributed to life. New possibilities are even percolating inside the old Miller apparatus. Revisiting Miller’s unsuccessful experiment from the 1980s, Bada discovered that high acidity inhibits the formation of amino acids in a carbon dioxide atmosphere. By increasing the realism of the early Earth simulation with the addition of carbonate minerals, he’s managed to boost the pH and make amino acids in abundance. All these potential pathways to life on Earth might mean we’ll never reach a deinitive solution to Darwin’s original conundrum. However, the wealth of opportunities helps resolve a related question that is equally profound. “The universe is pregnant with molecules ready to form and organize,” Hazen says. Searching for the source of life on Earth, Miller and Urey discovered the plausibility of life throughout the cosmos. D Jonathon Keats’ latest book is You Belong to the Universe: Buckminster Fuller and the Future (Oxford University Press).

November 2016 DISCOVER

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Mind Over Matter

Siren Song of Food To lose that extra weight, think less about food and more about environment. BY TAMAR HASPEL

One pound a week. It’s a common weight-loss goal thought by experts to be reasonable. By that reckoning, I should have lost 780 pounds in the 15 years I tried to lose weight. But I didn’t. Instead, I lost a paltry 25 — an inglorious rate of a half-ounce per week. Or that would’ve been the rate, had I used the entire 15 years to shed those 25 pounds. But that’s not how it happened. I couldn’t lose them, I couldn’t lose them, I couldn’t lose them. And then, suddenly, I could. What flipped the switch wasn’t a diet or an exercise plan. It was a book contract. Because the day I signed it, I quit my job. Working from home, I’d be out of reach of the doughnuts in the conference room or the jar of mini Snickers on my colleague’s desk. I igured that might make it easier to lose weight. And it did. Turns out there’s a body of research on just that subject — the siren song of food — and I’m not alone in my inability to navigate temptation successfully. One 2011 study of collegeage women found that overweight participants tended not to overeat when they weren’t actively tempted. However, according to the study’s authors, “the probability of overeating … increased rapidly as the number of good-tasting high-calorie foods increased.” Don’t I know it. So what makes some of us all but powerless in the presence of a cruller?

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I’m not sure we humans like to think of ourselves as inhabiting the same evolutionary plane as slobbering dogs, but we’re not so diferent. Just like them, yes, we need food, but we also like it. A SLAVE TO THE SYSTEMS Hedy Kober, who runs Yale University’s Clinical and Affective Neuroscience Lab and co-authored a 2016 research review on how we respond to food, sums it up: “Food cues. They make you eat more.” Those cues run the gamut. There’s the sight of food, the smell of it, even just a picture of it — they all make us want it. Just like the classic example of dogs drooling at the ring of a dinnertime bell, it’s out-and-out Pavlovian — a conditioned response to a stimulus. If Ivan Pavlov himself rose from the dead to check our salivary glands as

we walk past a Cinnabon, there’d be no surprises. I’m not sure we humans like to think of ourselves as inhabiting the same evolutionary plane as slobbering dogs, but we’re not so different. Just like them, yes, we need food, but we also like it. And that’s what makes food so tempting. “It’s true in your life, it’s true in my life, and it has a neurobiological explanation,” Kober says. Two different systems in the brain govern our food decisions. Our homeostatic system regulates our need for food and is controlled mainly in the hypothalamus (in the lower region of the brain). It regulates hormones that make us feel hungry or full and responds primarily to internal signals about our energy balance. The other — our hedonic reward system — is all about the liking. It’s complex and involves many parts of the brain, and it’s not even close to completely understood. But research has clearly shown that it makes us want to eat, even when we’re not hungry. The two systems aren’t completely separate, and hunger can amp up our hedonic reward system. Yet no amount of satisfying that hunger will shut it down.

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I’ve been there. I remember afternoon meetings when there was no earthly reason I should be hungry, staring down the damn cruller. The meetings were long. I stood no chance. I am Pavlov’s dog. We’re all Pavlov’s dogs. Or maybe we’re Pavlov’s secretaries. One workplace study, done about a decade ago, involved 40 secretaries and jars of candy. Researchers put candy jars, some clear and some opaque, either right on the secretaries’ desks or about 6 feet away. When clear jars were on the desk, the participants ate an average of 7.7 candies. When the jars were opaque, or far away, they ate fewer. But when the jars were both opaque and out of reach, consumption dropped 60 percent. A 60 percent drop, just by rejiggering the jar. Out of sight, out of reach, out of mind. A 2016 study published in the journal Appetite looked at this concept as well, but in Google’s millennialfriendly workplace where food and drink are available at any time. Before collecting data, the researchers saw that most people who came into the break room took a drink. So in half the break rooms, they put snacks next to the drinks. In the other half, the snacks were farther away. When the food was alongside the drinks, twice as many men and one-third more women helped themselves to the treats. Even when food is right in front of you, other cues also matter. You know that chocolate-chip-cookie smell? In one 2008 study, people trying to eat less actually ate 50 percent more cookies in the presence of the scent. Which brings up an important caveat. Some of us, myself included,

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I remember afternoon meetings when there was no earthly reason I should be hungry, staring down the damn cruller. he meetings were long. I stood no chance. I am Pavlov’s dog. We’re all Pavlov’s dogs. are more susceptible to food cues than others. And there’s good evidence that heightened responses to those cues can predict whether we put on a few pounds. In one 2015 study, researchers gave adolescents chocolate milkshakes and used fMRI scans to see how their brains reacted. “Elevated” responses — those that indicated a higher afinity for chocolate milkshakes — predicted fat gain three years later. But it’s not limited to just teens and milkshakes. Over and over, neuroimaging studies ind correlations between patterns of response to food cues and BMI or weight gain.

A DIET-FRIENDLY ENVIRONMENT So where do we go from here? Maybe we manipulate those food cues — not just our diets — to try and make a dent in our obesity epidemic. A head-slappingly simple way to tackle the issue? “Changing your environment is one potent solution,” Kober says. Boy, have I changed mine. Step into my kitchen, and all you’ll ind are ingredients. No pastries, no crackers and absolutely no crullers. On those rare occasions when I do have dangerous foods in the house — you can’t say no when your neighbor is selling Girl Scout cookies — I’ve been known to ask my husband to hide them and bring them out in limited quantities when my back is turned. It’s embarrassing, but it works. (Except when I ind the forgotten sleeve of Thin Mints, months later, in the ile drawer with the taxes.) Once you step outside the domain where you have control, though, it gets more complicated. It’s not a coincidence that the barbecue joint has a smoker going, or that the grocery store gives out samples, or that there’s an entire profession — food styling — dedicated to making food look delicious in pictures. So who decides whether — or how — we should limit exposure to food cues like advertising? Kober believes these are the kinds of hard questions we should be asking. Despite the temptations out in the world, in the nearly 20 years since I’ve had a J-O-B, I’ve kept the weight off — but it’s been a ight. So if you see me, do me a favor. Hide the jar. D Tamar Haspel writes about food, health and science.

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A H P I L R A NTAU T S E U C B r o

A fleet of tiny probes could reach the nearest star system within our lifetime. BY STEVE NADIS ILLUSTRATIONS BY ROEN KELLY

November 2016 DISCOVER

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Milner, a Russian native, was named after cosmonaut Yuri Gagarin, who exactly 55 years earlier became the irst man in space and the irst to orbit Earth. Milner was hoping to bring another historic irst to fruition. At a press conference held atop New York City’s One World Trade Center, he unveiled Breakthrough Starshot, a program with a bold agenda: to launch, within 20 years, a fleet of spacecraft that would within another 20 years reach the nearest star system, Alpha Centauri, 4.37 light-years away. Milner wasn’t just talking a good game; he was backing it with his own money, $100 million in research and development funding to demonstrate the feasibility of this wild idea. It might take another $10 billion to pull off the actual mission, but the main point Milner stressed during the press conference was that such an endeavor is within our grasp, assuming reasonable improvements in existing technology. He also brought along some heavy hitters to help make this case, including cosmologist Stephen Hawking, former astronaut Mae Jemison, Harvard University astrophysicist Avi Loeb and former head of the NASA Ames Research Center Pete Worden.

Russian entrepreneur Yuri Milner wants to launch tiny probes to the nearest star system.

“Today,” Hawking said, “we commit to the next great leap into the cosmos, because we are human and our nature is to fly.”

REACHING FOR THE STARS The enterprise got a boost on Aug. 24 when astronomers at the European Southern Observatory in Chile announced the discovery of an Earthlike planet orbiting Proxima Centauri, one of three stars in the Alpha Centauri system. “This announcement provides even more motivation for our mission,” claims Worden, who left NASA in 2015 to become executive director of the Starshot program. “Today we can make

The Breakthrough Starshot announcement included a bevy of space celebrities. From left to right: Yuri Milner, cosmologist Stephen Hawking, physicist Freeman Dyson, Cosmos Studios CEO Ann Druyan, astrophysicist Avi Loeb, astronaut Mae Jemison and NASA researcher Pete Worden.

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a better case for Starshot than we could have just a month ago.” While the excitement among Milner, Worden and their peers is palpable, they are not ignoring the immense technological issues that lie ahead. Yet two key ideas at the heart of this plan make the sci-i dream of interstellar travel scientiically plausible. The irst is limiting the spacecraft’s size so it weighs just a gram or two, allowing it to accelerate to unprecedented speeds. That strategy would, of course, require leaving people behind and going strictly robotic. The second idea is to leave the fuel behind as well, and propel the spacecraft solely with light. (Although photons are massless, they can still impart momentum.) This approach contributes to the goal of attaining speeds far beyond what conventional, chemicalpowered rockets could ever muster. The general concept of sail-bearing spacecraft — akin to the clipper ships of old, hurled across the seas by wind — is not new. Johannes Kepler alluded to this prospect in a 1610 letter to Galileo: “With ships or sails built for heavenly winds, some will venture into that great vastness.” While the physicist and sci-i writer Robert Forward further developed the idea in the 1960s, it remained far from practical implementation. During the media announcement, Milner cited recent critical advances that make sailing to the stars conceivable. Thanks to the dramatic decrease in the size of microelectronic components, researchers can now create suitably tiny space probes equipped with cameras, a power supply and navigational and communication capabilities. These “nanocraft” would be attached to ultrathin sails about a few square meters in area and weighing a few grams. A conventional rocket would carry hundreds to thousands of these nanocraft into space, releasing them into high-Earth orbit. Then a ground-based laser array with a combined capacity of 100 gigawatts of peak power, spread out over a dry, high-altitude site like Chile’s

BREAKTHROUGH INITIATIVES (2)

“For the first time in human history, we can do more than just gaze at the stars,” declared philanthropist and high-tech entrepreneur Yuri Milner on April 12. “We can actually reach them.”

A ground-based laser array in a high-altitude site like Chile’s Atacama Desert, shown in this artist’s rendering, could send 100 gigawatts of power to orbiting space probes, enough to accelerate them to a significant fraction of the speed of light.

Atacama Desert, would zap each sail, one at a time, for a few minutes. This would cause each wafer-like probe to accelerate to 20 percent of the speed of light (or about 134,000,000 mph) — about 1,000 times faster than today’s fastest space vehicles. The diminutive space probes would be inexpensive and, therefore, expendable; some could be lost due to technical glitches or collisions with space junk without jeopardizing the entire mission. It may sound crazy, but this plan might work. The stars could be within our grasp, as Starshot enthusiasts claim

— although it will still take tremendous progress to get there.

FROM DREAM TO REALITY So how close is this project to an actual liftoff ? Of the three technologies central to the effort, the space probe is the furthest along. At the April announcement, Milner held up a small wafer — less than 2 square inches in size and roughly 4 grams in mass — that can already meet many of the critical speciications. Designed by Harvard researcher Zachary Manchester, about half the wafer consists of a solar cell

for generating electricity, and the rest includes a small microprocessor, a radio transceiver and magnetometer, and a gyroscope for navigation and orientation. It’s all built from off-theshelf components at a cost of about $25. “The world’s smallest satellite,” Manchester calls it, “and probably the cheapest, too.” He hopes to get 100 of his satellites into space later this year, courtesy of a NASA educational program, to test radio communication methods in space. For future experiments, he wants to add more functionality to the probes

HOW TO REACH INTERSTELLAR SPACE

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3

A conventional rocket carries nanocraft into high-Earth orbit. Once in space, a launcher releases thousands of the tiny probes.

The accelerated probes then coast through interstellar space toward . . .

Alpha Centauri star system

TOP: BREAKTHROUGH INITIATIVES

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fee

D OORT CLOU

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A ground-based laser array zaps each sail, one at a time for a few minutes, causing each probe to accelerate to 20 percent of the speed of light (about 134,000,000 mph).

November 2016 DISCOVER

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The tiny probes could reach Pluto in three days, rather than the 9.5 years it took New Horizons to get there.

Gyroscope

Radio

Solar cell

Antennas

Microcontroller

Harvard researcher Zachary Manchester designed the “chipsat,” a tiny probe that may reach the nearest star system.

using cameras, while eventually trying out laser communications techniques. “Zac’s work was one of the key things that convinced Yuri and me that this might be feasible,” says Worden. Other aspects of this venture, however, are further from realization. That includes the proposed laser array, consisting of a large number (thousands, if not millions) of modest-sized ground lasers all pointed at a minuscule target, thousands of miles in the sky. “No one has ever done this on the scale we’re talking about,” says Philip Lubin, a physicist at the University of California, Santa Barbara. But there are no fundamental physics barriers, Lubin adds, “and there is now a credible path forward.” It’s a tricky problem, nevertheless. “For an array of one or several square kilometers, a laser on one side would see a different atmospheric density than a laser on the other

side,” explains Harvard astrophysicist James Guillochon. “We would need to correct for all of those differences.” Furthermore, Guillochon notes, the laser light hitting the sail has to be exactly on target. “You want an even distribution of energy on the sail so it doesn’t deform.” This leads to what may be the plan’s foremost challenge: coming up with a sail of a few square yards that’s suficiently strong, thin and lightweight. It also has to be highly reflective and absorb less than 1/100,000 of the incoming light so that it doesn’t melt. While no material yet devised meets all of the technical requirements, researchers have made progress on individual parts of the problem. After being sped up with laser beams, the Starshot probes would coast for the next 20 years, although it wouldn’t be smooth sailing. The nanocraft would face additional obstacles, primarily in the form of dust and gas encountered en route to the Alpha Centauri system. Princeton astrophysicist Bruce Draine estimates that the small spacecraft would sustain about a million collisions per square centimeter with dust grains during the journey — each one potentially a disaster at those speeds. Fortunately, there are ways of mitigating the damage. A beryllium

or graphite coating could protect the electronics, and as another precaution, researchers could reduce the number of collisions by folding up the sail after the nanocraft is beyond the reach of Earth-based lasers. The craft could also be directed to fly sideways, led by its thin edge to present less of a target. Worden hopes to sponsor a series of space experiments of increasing complexity in the coming years. Early experiments would involve solar sails, pushed strictly by sunlight, which have flown before. Others would involve pushing sails with lasers, which has not yet been done. “There’s a whole range of things we hope to do,” Worden says, “and we’ll build up gradually over time.”

SEEING THE SIGHTS There will be a lot to see along the way. Rather than being focused on a single destination — Alpha Centauri’s stars — this program, says Worden, “is really about a journey.” We’ll start by exploring our own backyard, the solar system, and move on from there, says Loeb, who heads the Starshot advisory committee. After all, he notes, the tiny probes “can reach Pluto in three days, rather than the 9.5 years it took New Horizons to get there.” The program could sacriice some of the multiple probes, he says, sending them “very close to targets we’re interested in. For example, we could fly through the plumes [of Enceladus] and see if we could detect the ingerprints of life.” The probes could also fly through the rings of Saturn or other harsh environments. “With cheap, fast spacecraft,” says Guillochon, “we could send one out to every asteroid in the asteroid belt or to every Pluto-like object in the outer solar system. With these small craft ready

HOW FAR AWAY IS ALPHA CENTAURI? Earth 1 AU

Jupiter 5.2 AU

Neptune 30 AU

Beginning of Oort Cloud 2,000 AU

Voyager 1 136 AU

Beginning of Oort Cloud 2,000 AU

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K U I P E R B E LT

End of Oort Cloud 50,000 AU

ZACHARY MANCHESTER

Magnetometer

OUR STELLAR NEIGHBORS Saturn

Uranus Jupiter

Neptune Starshade

KUIPER BELT

TOP RIGHT: NORTHROP GRUMMAN CORP.

Nearest star, Proxima Centauri: 24.7 trillion miles

Alpha Centauri A

1.2 t

r illi

To Proxima Centauri

on m

OORT CLOUD

iles

“Edge” of the solar system, the Oort Cloud: 4.6 trillion miles

Alpha Centauri B

1.0 billio mile n s

to launch, we could have hundreds of missions, each of them to a brand-new, never-before-seen world.” Speaking of new worlds, he says, “If Planet Nine exists, this would be one way to get there quickly.” There is no timetable set for missions like this, but if all goes according to plan, after 20 years of practice within the solar system, scientists may inally be ready for the irst extra-solar target, the Alpha Centauri system. It has three separate stars to survey. Proxima Centauri is the nearest, and the other two, Alpha Centauri A and B, are similar to our sun in mass and luminosity. What might a space probe see when it gets there? Proxima’s planet, dubbed Proxima b, is an obvious target. The rocky world of roughly Earth’s mass is in a tight orbit around its dim star, located in its “habitable zone.” Liquid water, and thus possibly life, might exist on its

Researchers at the McMath-Pierce Solar Telescope in Arizona test a 4-inch starshade, designed to precisely block out a star’s light, but not the light of orbiting planets.

surface. There’s also an unconirmed planetary sighting near Alpha Centauri B. University of Colorado astrophysicist Webster Cash, meanwhile, is trying out an innovative technique to see such planets directly. Cash, who participated in a Starshot workshop in April, is reflecting light from a telescope on Arizona’s Kitt Peak to a smaller, secondary telescope 1.5 miles away. In between, he’s placed a screen called a starshade to block the light of a test star to detect dimmer planets orbiting it. “The Starshot mission,” he says, “helps motivate those of us who want to look for planets; if and when we ind planets, that will really motivate the mission. And that’s the whole idea — to get everything moving forward.” So, barring any setbacks, the irst Starshot spacecraft would hopefully approach the Alpha Centauri system sometime around 2056. It would keep flying past, having no means of slowing

down. Ideally, the probe’s instruments will gather information about the newly found planet and relay it back to Earth, using the sail as an antenna to facilitate transmission. Even traveling at light speed, that data would take more than four years to arrive, a wait that no amount of technology can lessen. It’s an ambitious undertaking, to be sure, and success is not guaranteed — but where space travel is concerned, when is it ever? “We’re kind of where we were 40 years ago with gravity wave detectors,” Worden says. “People wondered if we could ever do this. It took decades, but they gradually made it work.” Starshot could be similar, he hopes. It wouldn’t be the irst time a giant leap began with a seemingly small step. D Steve Nadis, a contributing editor to Discover and Astronomy, is co-author of From the Great Wall to the Great Collider.

It’s a long way to the nearest star system. Humanity’s current distance record belongs to the Voyager 1 probe, launched in 1977, and that’s still only about 136 times the distance between Earth and the sun. Proxima Centauri’s almost 2,000 times farther.

Voyager 1 136 AU

OORT CLOUD

Astronomical Unit (AU) = 92,956,000 miles

Proxima Centauri 266,000 AU

Alpha Centauri A 279,000 AU

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MAMMOTH ISLAND The Ice Age giants of St. Paul Island outlived those on the mainland for millennia. What finally drove them to extinction? TEXT AND PHOTOS BY JESSICA MARSHALL

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An iconic example of the Ice Age megafauna of North America, the mammoth went extinct soon after humans arrived on the continent — except for isolated populations. WOOLLY MAMMOTH PHOTO BY STEPHEN WILKES, COURTESY OF THE ROYAL BC MUSEUM AND ARCHIVES, VICTORIA, BC, CANADA

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ST. PAUL ISLAND

Lake Hill

Cave where mammoth tooth was found in 2003

St. Paul Island, like the rest of the Pribilofs, was once part of the North American mainland. It was cut off from the continent beginning 11,000 years ago as the sea level rose.

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Pribilof Islands

Bering Sea

on this wind-battered speck of land for so many millennia after mainland populations perished, what inally killed them off ? Back in the 1960s, Paul Colinvaux, a British-born ecologist, had collected a sediment core from a lakebed on St. Paul. The preserved layers in the core revealed that the site held a sediment record stretching back at least 14,000 years — and the spot, Lake Hill, was only a quarter of a mile away from the cave where Graham had made his discovery. The answers to Graham’s questions might well lie in the dark mud of that lakebed. A decade after he found the tooth, Graham returned to St. Paul with his team of experts, ready to glean clues from new sediment cores about the intertwined history of the island and its mammoths.

GETTING TO THE BOTTOM OF A MYSTERY Weather complicates the early spring expedition to the largest of the Pribilofs, a cluster of volcanic islands poking up from the Bering Sea. Upon the team’s arrival to St. Paul, rain quickly turns to snow and they’re forced to stay in the island’s lone town. It’s home to most of St. Paul’s 500 residents, the majority of them Aleuts whose ancestors were brought here by Russian traders more than two centuries ago to work the northern fur seal killing ields. The team waits for the clouds to lift over the town’s skyline: the Russian Orthodox church’s onion dome, the brightly colored houses and the seafood processing plant. Blue-gray Arctic foxes native to the 40-squaremile island appear without fear outside home base, a research station run by the National Oceanic and Atmospheric Administration. At last, a bright morning arrives and the researchers head to Lake Hill, a crater lake encircled by a snowcovered rim. Graham’s team drills a hole through a foot of ice. Members thread together meter-long sections of pipe attached to a tube, or corer. With a splash they drive the assembly through the water and push it into the lakebed. Minutes later, the pipe is retrieved, the inal meter plugged with sediment layers preserved just as they were deposited. Within the muck lies a ALASKA forensic record of what fell, washed or otherwise Anchorage settled onto the bottom of this lake: fungal spores, fragments of plants, ancient pollen, volcanic ash, the remains of tiny crustaceans — and maybe even DNA from the mammoths themselves, shed while wallowing in the water. The

SATELLITE IMAGE: USGS/NASA LANDSAT. MAP: JAY SMITH

O

ne day thousands of years ago, on a tiny island in the middle of the Bering Sea, a woolly mammoth made a fatal misstep. It fell into a pitlike cave with no escape, and there it died. In 2003, another animal entered the cave — with a ladder. As he explored the space with his colleagues, Russell Graham, a paleontologist from Pennsylvania State University, lifted a rock near the back. There he found a single, pristine tooth from the mammoth, oblong and bumpy and as big as a loaf of bread. “It looked like you had just taken it out of the animal’s mouth,” says Graham, a tall, broad-shouldered man. With a beard and a slightly shuffling gait, he seems a bit of mammoth himself. He had handled hundreds of mammoth teeth in his career, but this tooth, from the Alaskan island of St. Paul, was special. It would send Graham and a multidisciplinary team of experts on a quest to reconstruct the animal’s environment and solve a mystery — one that has implications for species facing climate-induced extinction today. The mystery began when carbon dating established the tooth was just 6,500 years old. That’s several millennia fresher than any mammoth ind on the North American mainland. The date made Graham Paleontologist Russell Graham returned to St. Paul in 2013, a decade wonder: After the after finding an unexpected tooth. animals persisted

A resident of St. Paul holds a mammoth tooth found on the island (top left). The main settlement on St. Paul stands out in the snow on an early spring morning (top right). Things get messy drilling to obtain sediment cores at Lake Hill with researchers Nancy Bigelow, Matthew Wooller, Soumayha Belmecheri and Kyungsheol Choy (above, from left). The coring process is tricky in the extreme environment: Joints of the equipment freeze quickly, requiring the use of a blowtorch to maintain functionality (above, right). The research team treks through the snowscape of St. Paul Island to Lake Hill (below). The ice-covered crater lake has layers of sediment deposited over millennia that the scientists will use to reconstruct the mammoth’s environment, from the vegetation to the climate. By understanding the circumstances in which the animals lived, the team hopes to solve the mystery of why they died.

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University of Wisconsin-Madison guides the sixth segment into a tube, he notices the mud changes from a warm brown with a pudding-like texture to a blacker, irmer consistency. The team estimates it corresponds to deposits from roughly 6,000 to 8,000 years ago, spanning the period when Graham’s mammoth died in the cave. That means this segment could include the period of extinction, if mammoth DNA is present in its lower, older layers but absent from the top. “There’s mammoth in there,” Williams predicts.

At Lake Hill, researchers collect sediment cores by hand in a cold, messy process. Each meter-long core is placed in a tube for transport and then in a sleeping bag so the millennia-old mud won’t freeze, which could compromise the fine layers laid down over time.

team will use these bits of evidence to build a picture of how the island changed over millennia and, potentially, determine when the mammoths went extinct. Team members draw the sediment from below, meter by meter, extruding it into plastic tubes. The tubes are then sealed and tucked into a sleeping bag so they don’t freeze, which could distort the layers’ ine resolution. The work is messy, cold and physical. By day’s end, frozen mud crusts on the researchers’ clothing and clumps in their hair. Each meter of cored sediment reaches further back in time. As team member Jack Williams of the

MAMMOTHS’ LAST STAND St. Paul’s landscape of treeless tundra has likely changed little since the end of the last ice age, some 12,000 years ago. It’s easy to imagine where mammoths would have stood on the gentle slope, using their tusks to clear the snow while browsing for vegetation. In the summer, they would have trampled tiny tundra wildflowers as they lumbered to the lake, one of the main freshwater sources on the island. Researchers estimate that mammoths disappeared from North America’s mainland 10,000 to 14,000 years ago. But they persisted on St. Paul for millennia after that. The animals also survived — for even longer — on Wrangel Island, deep in the Russian Arctic. Researchers there have found teeth that are only 4,000 years old; the Wrangel mammoths were alive as Egypt erected its great pyramids. Like Wrangel, St. Paul hasn’t always been an island. At the peak of the last ice age, around 21,000 years ago, it was a volcanically active spot on the southern edge of the Bering Land Bridge. Mammoths, saber-toothed cats,

NORTH AMERICAN MEGAFAUNA EXTINCTION based upon direct radiocarbon dates on bones or teeth Woolly mammoth

12,397 – 12,016

Mammuthus primigenius

Columbian mammoth

12,919 – 12,189

Mammuthus columbi

American mastodon

12,800 – 12,687

Mammut americanum

*Beautiful armadillo

13,017 – 12,728

Dasypus bellus

*Stag moose

13,276 – 13,011

Cervalces scotti

Giant beaver

12,823 – 12,673

Castoroides ohioensis

Jefferson’s ground sloth

13,180 – 13,034

Megalonyx jeffersonii

Harlan’s ground sloth

14,128 – 14,788

Glossotherium harlani

*Flat-headed peccary

13,070 – 12,775

Platygonus compressus

Short-faced bear

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0 00 11 ,

00 12 ,

0 00 13 ,

0 ,0 0 14

00 ,0

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*not pictured

0

12,971 – 12,725

Arctodus simus

short-faced bears and other large animals, or megafauna, roamed the passage between North America and Eurasia. Then, around 11,000 years ago, the climate began to warm and sea level rose, swallowing the land bridge and turning the area into an island over the next 2,000 years. The mammoths were trapped, but their very isolation may have protected them — at least for a while. Researchers debate what caused the mammoths to die out on the mainland at the end of the last ice age. Some say it was the changing climate, while others argue that humans were the culprits, hunting mammoths to extinction. Even within Graham’s team, there’s a friendly difference of opinion. “To me, one of the telling patterns is that the timing of extinction around the world roughly corresponds to the timing of human migration dispersion around the world,” says Williams, who sees humans as the major culprits. On the mainland of North America, the arrival of humans, climatic changes and the mammoth’s extinction happened at roughly the same time. But mammoths weathered many other climatic shifts over the hundreds of thousands of years they roamed Earth, Williams notes. Graham, on the other hand, thinks climate was the driving force. Humans may have sped things up, he says, but mammoths and other Ice Age megafauna were on their way out anyway. “I think the extinctions would have occurred whether humans came or not,” he says. He believes each climate shift that the mammoths

survived actually weakened the species, pushing them closer to extinction. The cores of sediment from Lake Hill won’t settle the general megafauna extinction debate: St. Paul’s isolation likely sets it apart from whatever influence humans had on the mainland mammoth population. There’s no evidence that humans ever made it to this dot of an island before Russian fur traders arrived in the late 1700s. On St. Paul, at least, the more likely suspect is climate change, though it’s also possible that the inal straw for mammoths here was habitat loss: With increasing sea levels, the island may have become too small to sustain its megafauna population.

Researchers estimate that mammoths disappeared from North America’s mainland 10,000 to 14,000 years ago. But they persisted on St. Paul for millennia after that. Determining what happened to St. Paul’s mammoths isn’t purely a historical exercise. Many species worldwide currently face the same pressures: changing climate, human encroachment, rising seas. “This is hugely relevant to today,” Williams says. “Can climate change alone cause species to go extinct? Or is the story that climate change is a stressor that makes populations more susceptible to extinction when combined with other stressors?” The most recent major die-off event, at the end of the Pleistocene some 11,000 years ago, “has direct carryover to how we think about the current wave of extinctions and how to minimize them,” Williams says. The end of the last ice age was a dynamic time in North America. Glaciers melted, opening up new land corridors, but sea levels rose, shrinking land mass. Humans arrived from Siberia, and North America’s massive animals went extinct. Researchers still debate why the megafauna died off: Hunting by humans and climate change are the main suspects.

0

to present

5, 00

0 00 6,

0 7,

00

00 0 8,

00 9, 0

10 ,0 0

0

Age of mammoth tooth found on St. Paul Island in 2003

Years before present ALISON MACKEY/DISCOVER; DATA COMPILED BY RUSSELL W. GRAHAM, THOMAS W. STAFFORD JR. AND H. GREGORY MACDONALD; SCALE REFERENCE: PREHISTORIC-WILDLIFE.COM

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After four days of coring — interrupted at one point by a blizzard — the team has 400 pounds of mud in 45 meters of tubing to ship to a Minnesota lab, where the next chapter in the mystery unfolds.

THE DETECTIVES It’s May in Minneapolis when the team is reunited with their mud at the University of Minnesota’s National Lacustrine Core Facility — as the name suggests, a repository for lake-based sediment cores. Staff at LacCore have already sliced the cores in half and taken high-resolution photos. Graham and colleagues from various disciplines will spend three days cutting the cores into tiny pieces using stainless steel spatulas. They’ll divide the thousands of samples among little plastic boxes to take back to their respective labs, which spread across North America, as the mammoths once did. Beth Shapiro at the University of California, Santa Cruz, gets irst dibs on the samples since her team will take on the most sensitive test, at greatest risk of contamination during handling: the search for ancient mammoth DNA in the layers of sediment. With the help of a graduate student, Williams will look for a kind of mammoth proxy: sporormiella, a fungus that lives in the dung of large herbivores, and grains of ancient pollen that can reveal what kind of vegetation once grew around the lake. At the University of Alaska Fairbanks, Matthew Wooller and colleagues will analyze the mud for the remains of diatoms, water fleas and other tiny life to learn about the water temperature and clarity over time.

the African elephant. It’s a match. Even better: In 2015, they’re able to compare the sediment DNA with newly-sequenced mammoth DNA from a separate team of researchers. It was another match in all core samples from 5,650 to 10,850 years old, the oldest sediment they’d collected on St. Paul. To rule out a random match, the team compares the sediment DNA with that of a two-toed sloth, an animal with zero chance of being found in the Arctic in the last 12,000 years. As a further check on their work, they also compare the unclassiied sediment DNA to that of the animals most likely to contaminate a sample, including humans. The DNA sequences don’t align, which makes Shapiro and her team conident that what’s in the sediment really belonged to a mammoth. Meanwhile, Williams’ team inds the sporormiella they are looking for, as well as two other fungal spores associated with dung that can serve as additional proxies for an actual mammoth. “Of the three spore types, two disappear from the core’s sediment layers within 2 centimeters of each other, which would be the equivalent of a few decades,” Williams says of the mammoth dung-loving fungus. The ancient mammoth DNA disappears at the same point. “Having the proxies match that well is what you always hope for but rarely attain,” he says. When Froese’s lab identiies a core sample layer of volcanic ash from a known eruption in the area 3,595 years ago, it gives added conidence to the teams’ timeline. The multidisciplinary effort establishes that the

With the mud distributed, the researchers disperse. hey will spend more than two years analyzing and discussing the muck as they try to pinpoint when the mammoths went extinct, and to understand why. Duane Froese at the University of Alberta will look for layers of volcanic ash in the sediment that can be linked to known eruptions in the region. This, along with carbon dating of tiny plant pieces found in the mud, will allow the team to put irm dates at points along the mud core, calibrating it in time. Ash layers may also implicate or rule out a volcanic eruption as the cause of the mammoths’ extinction. With the mud distributed, the researchers disperse. They will spend more than two years analyzing and discussing the muck as they try to pinpoint when the mammoths went extinct, and to understand why.

IT’S A DATE Shapiro’s team irst compares unclassiied DNA sequences found in the sediment samples with the genome of the mammoth’s closest surviving relative,

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At the National Lacrustine Core Facility in Minnesota, samples from the St. Paul Island sediment cores are divided into plastic containers that will be sent to labs at institutions across the country (left). Researcher Peter Heintzman (middle) is one of the team members involved in the effort. Not everything from St. Paul Island is muddy: The team collected vegetation (right) to compare it with ancient pollen and other clues to the environment stored in the sediment cores to learn how the island has changed over time.

mammoth’s extinction occurred 5,600 years ago, plus or minus a century. “We have one of the best constrained times of extinction for mammoths anywhere — and maybe for any prehistoric extinction,” Williams says. With the end-date for the St. Paul mammoths now conidently established, the researchers can use it to solve the biggest part of the mystery: What inally killed the animals?

THE FINAL BLOW Graham and several of the other team members begin by ruling out possible causes, such as a change in vegetation to something less mammoth-friendly. Pollen in the core samples reveal that herbaceous plants on the island gave way to shrubs, but only after the mammoths’ extinction. It’s possible that a climate shift changed the composition of the plant communities — or the shrubs may have become dominant simply because the mammoths were no longer stomping around, keeping their growth in check. The data does show a modest rise in temperature that predates extinction. With the melting ice and rising seas of the End-Pleistocene, the island began to shrink rapidly until about 9,000 years ago. At that point, the rate of land loss slowed until St. Paul reached its current size, smaller than the city of San Francisco, around 6,000 years ago. The shrinking island would have downsized the mammoth population, too, as resources grew scarce. But the inal straw, the team concludes, is something of a surprise. Beginning about 7,850 years ago, the variety and number of diatoms and water fleas found in the sediment change in a way that indicates the water was becoming shallower and murkier. The lake began to dry

up — the modest bump in temperature was apparently enough to increase evaporation. The mammoths were losing their main watering hole. “Elephants need fresh water every day,” Graham says. “They drink 70 to 200 liters per individual. There’s no reason to think mammoths were different.” Thanks to a combination of diminished island size, rising temperature and perhaps the animals themselves causing erosion and fouling their own water, the mammoths died of thirst. The team solved the mystery of the St. Paul mammoths’ demise. But why they persevered may, paradoxically, be harder to answer. It’s reasonable to propose that their isolation protected them from human activity — but that idea is dificult to prove, and Graham suggests mainland vegetation may have changed in ways St. Paul’s didn’t. Either way, their isolation eventually came with a downside: When environmental changes made the island less habitable, they had nowhere to go. It’s a cautionary tale about the vulnerability of island populations today. “Usually we’d say this was an insigniicant climate change, but on St. Paul, it turned out not to be,” Graham says. While water was the crucial factor there, it could be other limitations — habitat or availability of food — for other species in other places. Graham adds: “This research suggests that many island populations, not just in the Bering Strait but throughout the world, could be jeopardized by coming climate change.” D Jessica Marshall is a writer based in Seattle.

Explore more of Mammoth Island through our writer’s eyes at DiscoverMagazine.com/MammothIsland

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James Allison of MD Anderson Cancer Center in Houston has figured out how to defeat cancer at its own game.

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SCOTT DALTON

CHECK

How an iconoclastic cancer researcher gamed the immune system and unleashed a potent new weapon against the disease.

By the middle of her senior year at West Virginia University, Sharon Belvin knew something was wrong. The slim, blond 22-year-old was growing increasingly short of breath during her daily runs, but doctors couldn’t pinpoint the cause. Then, shortly before graduation, she discovered a hard lump beneath her left collarbone. A biopsy identiied it as melanoma — the deadliest form of skin cancer, killing 10,000 Americans annually. Worse, a CT scan showed masses scattered throughout her chest. Belvin faced a crushing prognosis: For Stage IV metastatic melanoma, average survival is measured in months. Still, she was determined to ight. In May 2004, she returned home to New Jersey, married her high school sweetheart and started chemotherapy at Memorial Sloan Kettering Cancer Center in New York City. The treatment caused debilitating nausea and neuropathy, but the shadows on her scans continued to multiply. That December, Belvin’s oncologist informed her that the cancer had spread to her brain. After surgeons used radiation to burn away the tumor, she was switched to interleukin-2, a naturally occurring protein that, in high doses, sends the body’s immune defenses into overdrive. Although IL-2 triggers remission in a small percentage of patients, its side effects are often horriic. Belvin endured violent vomiting, peeling skin and episodes of delirium, but she didn’t get better. As the cancer illed her chest cavity with fluid, her hope began to drain away. That’s when the oncologist told her about a clinical trial just getting underway, of a medication called ipilimumab. The drug’s mechanism of action was entirely new: Instead of attacking cancer cells (like chemo), or indiscriminately revving up the immune system (like IL-2), ipilimumab blocked a single receptor on one type of immune cell. “Would you like to try it?” the doctor asked. “The choice was to do nothing and die, or take a chance,” Belvin recalls. “It was the easiest decision I ever had to make.” In September 2005, she received the irst of four 90-minute infusions, spread over a 12-week period. The only adverse effect was a daylong spell of shaking and sweating. Soon, she felt well enough to walk her dog again. Her tumors were shrinking dramatically, and they kept doing so for months after her inal session.

MATE BY KENNETH MILLER

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KIERAN KESNER

certain lung cancers. Dozens more are in development. At oncology conferences, speakers use the phrase “paradigm shift” when discussing these therapies. Checkpoint inhibitors already produce unprecedented rates of long-term remission for a handful of hard-to-treat cancers, but their potential is even greater: Because such drugs modify the body’s response to cancer, rather than the cancer itself, they could theoretically be effective against almost any kind of malignancy. Allison’s brainchild — and the pioneering research that led to its birth — has brought him a renown that’s rare among his peers. “He’s one of our rock stars,” says Jaffee. Yet at 67, he remains true to his bar-band roots — literally. Allison has played in blues-rock groups since his 20s, and he currently fronts an all-cancer-researcher combo called the Checkpoints. Round-faced and rotund, with long, gray hair and a scruffy beard, he blows harmonica and contributes occasional vocals, belting out classics like “Big Boss Man” in a gravelly baritone. In his day job, at the University of Texas MD Anderson Cancer Center in Houston, Allison serves as chair of the immunology department, deputy director of the David H. Koch Center for Applied Research Sharon Belvin of Genitourinary Cancers and executive director of the immunotherapy division of By September 2006, they’d vanished. After declaring the Moon Shots Program, a multidisciplinary effort Belvin in remission, the oncologist introduced her to the tackling cancer mortality. In his cluttered ofice, a Willie man behind ipilimumab, immunologist James P. Allison. Nelson poster hangs amid the diplomas and trophies Belvin burst into tears. Then she hugged him so hard, she — a memento of a long-ago jam with the master. In nearly knocked off his glasses. conversation, Allison can seem shy and distracted until he gets onto a topic that excites him. Then, his eyes MOON SHOT MAN sparkle, and the words come at warp speed. That was Allison’s irst encounter with a patient whose “I just like to have fun with it,” he says when asked life he’d helped to save, and he still chokes up when he about his music, and he speaks of his scientiic pursuits recalls the moment. Over the past decade, he’s been in almost identical terms. As with any good bluesman, the recipient of many such embraces — as well as an however, Allison’s sense of fun is informed by tragic array of honors, including the 2015 Lasker-DeBakey experience. To grasp the passion that drives his work, it Clinical Medical Research Award, often a precursor helps to glimpse the pain that shaped his youth. to a Nobel Prize. The class of medications that he CONFRONTING CANCER AT AN EARLY AGE conceived, known as immune checkpoint inhibitors, Allison grew up in the small oil town of Alice, Texas, works counterintuitively: By turning off one of the the youngest of three brothers. His father was a country immune system’s built-in safeguards, the inhibitors doctor, his mother a homemaker. She was seriously ill allow T cells — the system’s foot soldiers — to attack for several years, but no one mentioned that she had tumors more effectively. lymphoma until shortly before she died — with Allison, “Jim’s work has really allowed immunotherapy to who was 11, holding her hand. “I saw the burns on her become a game changer for patients with cancer,” says neck from radiation treatment,” he recalls, “but I didn’t Elizabeth Jaffee, deputy director of the Sidney Kimmel know what they were. Back then, people didn’t talk Comprehensive Cancer Center at Johns Hopkins. Since about cancer.” approving ipilimumab ive years ago, the Food and Over the next few years, Allison watched an uncle die Drug Administration has OK’d two similar drugs — of melanoma, and another of lung cancer. Meanwhile, pembrolizumab and nivolumab — for melanoma and

he began showing an obsessive interest in science — as well as a rebellious streak. He got in trouble for talking out of turn and playing hooky. When he learned that his high school biology teacher refused to teach evolution for religious reasons, he boycotted the class. A counselor suggested he take a correspondence course from the University of Texas instead. Studying solo in a room near the gym, Allison stoically bore the taunts of jocks and coaches. He graduated early, at 16, and enrolled at UT Austin as a premed. Soon, though, he realized that he didn’t want to follow in his father’s footsteps. “I thought how scary it was to be a physician and have someone’s life in your hands,” he says. “In medicine, you have to be right all the time. In science, you learn by being wrong.” He wound up with a bachelor’s degree in microbiology, and he went on to earn a Ph.D. in biological science. Allison didn’t set out to be a cancer researcher; he dreamed of solving some of the basic mysteries of biochemistry. But in graduate school, when he was assigned to tinker with the formulation of a common chemotherapy for leukemia, his family history prompted him to try an experiment of his own, one that would deeply influence his career direction. Allison wondered what would happen if he injected mice with tumors after they were cured. To his astonishment, the animals didn’t get leukemia again. Somehow, he surmised, their immune systems had learned to kill the tumors.

By 1973, when Allison inished his doctorate, the mechanics of immunity were somewhat better understood than in Coley’s day. For example, researchers had recently identiied T lymphocytes, white blood cells that destroy pathogens in several distinctive ways. Each T cell, scientists believed, was programmed to recognize a particular snippet of protein, or peptide, unique to invaders such as bacteria, viruses or tumor cells. These bits of protein are categorized as antigens, substances capable of triggering an immune response. When a T cell detects one, it morphs into a ighting machine, zapping invaders with lethal chemicals, multiplying into an army of identical killers or signaling other immune-system troops to join the attack. Yet exactly how T cells are activated remained largely a matter of conjecture. Those leukemia-resistant mice spurred Allison to explore the immune system’s uncharted territory. He did a postdoctoral fellowship in molecular immunology at the Scripps Clinic and Research Foundation in La Jolla, Calif. Then, in 1977, he headed back to Texas, as an assistant biochemist at MD Anderson’s new Cancer Center Science Park in Smithville. One of immunology’s great unknowns was how T cells recognized the antigen that marked an invader for destruction. Researchers presumed that each T cell bore a receptor on its surface, shaped to it a foreign peptide like a lock its a key. But no T cell antigen receptor (TCR) had yet been identiied.

THE UNIVERSITY OF TEXAS/MD ANDERSON CANCER CENTER

Allison didn’t set out to be a cancer researcher; he dreamed of solving some of the basic mysteries of biochemistry. But in graduate school, his family history prompted him to try an experiment of his own, one that would deeply influence his career direction. The notion of harnessing immune defenses to ight cancer dates back to the 1890s, when a New York surgeon named William Coley learned that some patients with sarcomas went into remission after contracting a Streptococcus infection. It seemed the body’s attack on the microbes wiped out the tumors as well. Coley began inoculating cancer patients with the same strain of strep; a few died of the infection, but others emerged tumor-free. When he switched to dead bacteria, patients’ survival rates improved. Coley’s Toxin, as it became known, was widely used for 40 years. But its results were unpredictable, and the concept of cancer immunotherapy fell out of favor as the ield focused on chemotherapy and radiation. Although a few scientists continued to probe the potential of immune-based approaches, their work was mostly ignored.

James Allison, late 1970s

Allison decided to go hunting. If a TCR was a hidden lock, he reasoned, the logical way to ind it was to fashion a key and poke around until something clicked. The kind of key he had in mind had only recently been developed: a monoclonal antibody. Researchers had discovered how to custom-manufacture antibodies — naturally occurring molecules that target speciic antigens — through cloning. These designer antibodies could be used, among other things, to detect and manipulate cellular receptors. Allison began by injecting a mouse with lymphoma tumors to trigger an immune response. He and two colleagues then used spleen cells from the animal to grow 43 cell lines. Next, Allison’s team exposed the cell lines to the mouse tumors. One of the 43 began producing a new protein, which the researchers took to be an antibody to

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Checkpoint Inhibitors at Work A new class of drugs turns off the immune system’s safeguards in a couple of different ways, so T cells — the foot soldiers — can attack tumors more effectively.

KILLING A KILLER Over the next few years, immunologists learned that it took more than an encounter between a TCR and an antigen to trigger a T cell’s killer mode. In the late 1980s, researchers began to suspect that a second signal, from an unidentiied player, was required before activation could occur. It was Allison’s team that identiied a T cell protein called CD28 as the crucial co-stimulator — the gas pedal to the TCR’s ignition switch. But controversy arose in 1991, when a team led by pharmaceutical researcher Peter Linsley identiied another protein molecule, CTLA-4, which closely resembled CD28 and was found only on activated T cells. Linsley theorized that CTLA-4 was another co-stimulator. Immunologist Jeff Bluestone, at the University of Chicago, disagreed: His experiments suggested that CTLA-4 subdued T-cell activation. Allison, using different methods, came to a similar conclusion. The molecule seemed to function as a checkpoint, turning off the T cell after a period of activity — perhaps to prevent collateral damage to healthy tissue. That got Allison thinking about the disease that took his mother. Why didn’t the immune system nip every cancer in the bud? Sometimes, he speculated, it was because CTLA-4 deactivated T cells before they could inish off a clump of tumor cells. If that were the case, simply stomping on the gas, with immune stimulators such as Coley’s Toxin, or the IL-2 initially used to treat Sharon Belvin, would be of limited use. Inhibiting the checkpoint — releasing the T cell’s metaphoric brakes — might be a more productive approach, Allison thought. In 1995, Allison’s team created a monoclonal antibody designed to block the CTLA-4 receptor, effectively shutting down the checkpoint. They injected it into tumor-bearing mice. In the untreated control group, the animals died; in the treated group, 90 percent rejected their tumors and survived. “It was too good to be true,” Allison later wrote. “I didn’t believe the initial results.” He repeated the experiment. For two weeks, the tumors in all the mice continued to grow, and Allison braced himself

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antigens

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blocks the checkpoint antigenpresenting cell activation molecule

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Two of the drugs act to block the inhibitory checkpoint on T cells, boosting T cell responses against tumor cells.

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One molecule drug blocks an inhibitory molecule on T cells. This allows activation molecules to function so that T cells can attack cancer cells.

for disappointment. Then the tumors in most of the treated mice again melted away. Allison’s team went on to test anti-CTLA-4 against a variety of cancers, both alone and in combination with vaccines and chemotherapy. The responses continued to be encouraging — and enduring. Because the checkpoint inhibitor targeted T cells rather than tumor cells, cancers didn’t readily respond by mutating and developing resistance, a common problem with chemotherapy. Meanwhile, each mouse retained an immunological memory of the tumor it had vanquished, which curbed recurrence. After publishing his indings in 1996 in Science, Allison went looking for a pharmaceutical company to develop a CTLA-4 inhibitor for humans. He ran into a wall. Since the demise of Coley’s Toxin, several types of immunotherapy had showed promise in animal models, only to fail in people. The few that worked either had narrow applications or marginal success rates. For two years, Allison got nothing but rejections, but his old stubbornness kept him going. At last, a small New Jersey-based company called Medarex said yes.

JAY SMITH

the tumor antigen. Chemical analysis showed that its structure resembled that of a protein found on T cells. In 1982, Allison published a paper in The Journal of Immunology suggesting “the possibility” that the look-alike protein on T cells might be a TCR. Soon afterward, other researchers conirmed that it was. Armed with his irst big discovery, Allison won a full professorship at the University of California, Berkeley, where he became co-chair of the department of molecular and cell biology and director of the cancer research lab.

Its scientists began working with Allison to develop the new medication. And by 2001, ipilimumab was ready for testing.

TRIALS AND TRIBULATIONS In Allison’s ofice, there’s a drawing of him playing harmonica, captioned “The Cancer Immunotherapy Clinical Trial Blues.” The trials for ipilimumab involved about 5,000 patients who had received the drug. In 2004, Allison moved from Berkeley to Memorial Sloan Kettering to work with the scientists leading the study — including Sharon Belvin’s oncologist, Jedd Wolchok. The following year, Allison underwent a prostatectomy for prostate cancer, and his middle brother died of the disease. The return of the family curse underscored the urgency of his research, and made its deliberate pace harder to bear. At irst, the trials went badly. Few patients made progress by 12 weeks, the point at which chemotherapy is usually assessed. But clinicians eventually found that with ipilimumab, many tumors began shrinking later. In fact, ipilimumab proved to be the irst medication to signiicantly expand median survival rates in patients with advanced melanoma — from six months to 11.

with different characteristics respond to different immunotherapies: She would treat patients before their growths were surgically removed, then analyze the tissue in her lab. “We did some grants together, and then we started going together,” Allison recalls. “At some point, we decided we might as well get married.” They tied the knot in 2014. Sharma emigrated from Guyana as a girl; a driven personality formed during early struggles with poverty and a serious injury, along with her obsessive brilliance, made her an ideal match for Allison. “We both live and breathe science and medicine,” she says with a laugh. “Jim gives entire lectures on T cells in his sleep.” Since Allison hatched the idea of blocking CTLA-4, several more immune checkpoints have been identiied. “What he showed us is turning the immune system on isn’t enough; the crucial step is to make sure it doesn’t turn itself off,” says Antoni Ribas, director of the tumor immunology program at UCLA’s Jonsson Comprehensive Cancer Center. “Now we’re trying to understand which brakes need to be taken out and which gas pedals stepped on to achieve the maximum beneits.” Pembrolizumab and nivolumab, for example, the newest inhibitors to win FDA approval, target a checkpoint

Sharma had developed a new method for studying how tumors with diferent characteristics respond to diferent immunotherapies: She would treat patients before their growths were surgically removed, then analyze the tissue in her lab.

NICK DE LA TORRE

Padmanee Sharma

More important, nearly a quarter of patients survived for more than three years. Most of that group was still alive a decade later. And although some patients experienced serious side effects, such as colitis or hepatitis, these could usually be controlled with relative ease. In 2011, the FDA approved ipilimumab for melanoma, and the pharma giant Bristol Myers-Squibb — which had acquired Medarex — began marketing it as Yervoy. (Approval was later expanded to non-small-cell lung cancers.) Soon afterward, Allison returned to MD Anderson, lured by the opportunity to launch the center’s $30 million Moon Shots immunotherapy research program. He was also attracted by the prospect of working more closely with the program’s scientiic director, Padmanee Sharma, an oncologist and researcher with whom he’d collaborated in the past. Sharma had developed a new method for studying how tumors

called PD-1, through which tumors can induce a T cell to deactivate. Studies show that PD-1 inhibitors are effective for a larger proportion of melanoma patients than ipilimumab alone — and, in combination with that drug, they achieve a two-year survival rate of 80 percent. More than 500 clinical trials are underway to explore the impact of these and other checkpoint inhibitors on a dozen varieties of cancer, alone or with other immunotherapies, as well as conventional treatments. For thousands of patients, Allison’s passion and persistence have already paid off. “I owe Jim so much,” says Belvin, now a personal trainer, health educator and a mother of two. “As far as I’m concerned, he deserves the world.” D Kenneth Miller is a Los Angeles freelance writer who contributes frequently to Discover.

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Like pictographs from an alien world, some of Earth’s earliest animals appear as subtle marks on Newfoundland’s Mistaken Point.

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BY ROBERT MOOR

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BARRETT & MACKAY/GETTY IMAGES; ILLUSTRATIONS BY DAVID A. JOHNSON

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Half a billion years ago, a creature slithered across the seafloor for the first time. It may have launched an evolutionary arms race.

November 2016 DISCOVER

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(Dickinsonia)

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But this hike was a mere diversion, a side trip. My ultimate destination was a yet more baffling and inaccessible wilderness: the distant past. I was making my way to a rocky outcropping on the island’s southeast corner, where I hoped to ind the oldest trails on Earth. These fossil trails, which are roughly 565 million years old, date back to the dimmest dawn of animal life. Now fossilized and faint, each one is roughly a centimeter wide, like a ingertip’s errant brush across the surface of a drying clay pot. I had read all about them, but I wanted to touch them, to trace their runnels like a blind man. I hoped that encountering them up close would resolve a question I’ve long harbored: Why do we, as animals, uproot ourselves rather than maintaining the stately ixity of trees? Why do we venture into places where we were not born and do not belong? Why do we press forward into the unknown?

CARDINAL CRAWLERS The world’s oldest trails were discovered one afternoon in 2008 by Alex Liu, now a researcher at the University of Bristol. He and his research assistant were scouting for new fossil sites out on a rocky promontory called Mistaken Point, where a series of well-known fossil beds overlook

TOP: BARRETT & MACKAY/GETTY IMAGES. BOTTOM: SCOTT LESLIE/MINDEN PICTURES

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It is impossible to fully appreciate the value of a trail until you have been forced to walk through the wilderness without one. There is a practical reason why, for more than a thousand years, after the fall of Rome and before the rise of Romanticism, little was more abhorrent to the European mind than the prospect of a “pathless” or “tangled” wilderness. Pathless wildernesses still exist in the modern world, and at least some have retained their power to elicit dread. I have visited one such place. It lay on the northern rim of a glacial fjord called Western Brook Pond, on the island of Newfoundland, in Canada’s easternmost province. If you want to be taught (however harshly) the blessing of a well-marked trail, go there. To cross the fjord’s stygian waters, I had to hire a ferryboat. On the far side of the fjord, the captain dropped me and four other hikers off at the base of a long ravine, where a series of animal trails led through a dense fern jungle and up a granite cliff face bisected by a waterfall. At the top of the ravine, I found a vast green tableland. The trail I had been following vanished altogether. Soaked in sweat from the hike up, I took a moment to rest, my feet dangling over the cliff’s edge. At the ragged western edge of the tableland, it abruptly dropped hundreds of feet to the fjord’s indigo water.

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This rugged Newfoundland outcrop (above) is a hotbed of research into the mysterious Ediacaran creatures. A hiker explores Mistaken Point (left) where, 565 million years ago, Ediacarans left imprints in the coastal rock.

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the North Atlantic. Bordering one surface, Liu noticed, was a small shelf of mudstone that bore a red patina. The red was rust — an oxidized form of iron pyrite, which commonly appears on local Precambrian fossil beds. They scrambled down the bluff to inspect it. There, Liu spotted what many other paleontologists before him had somehow missed: a series of sinuous traces thought to be left behind by organisms of the Ediacaran biota, the planet’s earliest known forms of animal life. The ancient Ediacarans, which likely went extinct around 541 million years ago, were exceedingly odd creatures. Soft-bodied and largely immobile, mouthless and anusless, some were shaped like discs, others like quilted mattresses, others like fronds. One unfortunate type is often described as looking like a bag of mud. We can envision them only dimly. Paleontologists don’t know what color they were, how long they lived, what they ate or how they reproduced. We do not know why they began to crawl — perhaps they were hunting for food, fleeing a mysterious predator or doing something else entirely.

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project, then I’d have been trying to answer questions that people have looked at for hundreds of years,” he said. “Whereas I knew that Ediacaran stuff was new, uncertain. And that was more enticing, really, because the questions are bigger.” Of all the manifold questions surrounding these elusive, soft-bodied organisms, the biggest might concern the origins of animal movement. Some paleontologists theorize that the irst Ediacaran trail-maker may have set off a series of morphological changes. This led animal life, in its and starts, from a serene garden of swaying anemone-like creatures to today’s violent, skeletonized kingdom of sprinters, jumpers, fliers, swimmers, diggers and walkers. It is rare in science to run across a big new question, and harder still to answer it, but Liu seemed to have this one by the scruff of its neck. For a respectable scientist, wading into the murky world of the Ediacarans is a treacherous endeavor. Information about that distant era is extremely limited, and even the most basic assumptions often prove unreliable. For instance, we still do not know for certain which kingdom of

Soft-bodied creatures are rare in the fossil record (above). And that makes Mistaken Point a key site for paleontologist Alex Liu (right), who’s trying to understand the origins of animal movement.

(Swartpuntia)

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A PATH LESS TRAVELED As a boy, Liu loved dinosaurs, particularly those in Jurassic Park. The romance of those craning beasts, which he never fully outgrew, coupled with his love of ieldwork and knack for geology, drew him to fossil hunting. When he was pursuing his master’s degree at Oxford, he had planned to study ancient mammals, but he found the ield crowded; his thesis project was spent studying the teeth of Eocene-era elephants in Egypt. For his Ph.D. work, he turned to the much older and largely unstudied Ediacaran biota. “If I had taken on a mammal

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life the Ediacarans belonged to. At various times, it has been proposed that they could have been plants, fungi, colonies of single-celled organisms or, according to the trace fossil expert Adolf Seilacher, a “lost kingdom” called Vendobionta. While most Ediacaran researchers tentatively agree that they were animals, recently, some have begun arguing that lumping all the known Ediacaran species into one kingdom or another may be too reductive, and each fossil must instead be re-assessed one by one.

ALIEN EARTH As I sat next to him at dinner one night in the Newfoundland town of Trepassey, it seemed odd to me that Liu, a soft-spoken and exceptionally careful researcher, was drawn to such a ield. Liu told me he irst became interested in Ediacarans

LEFT: ALEX LIU. RIGHT: EMMA LIU

Despite all these uncertainties, what Liu’s trails undoubtedly suggest is that 565 million years ago, a living thing did something virtually unprecedented on this planet — it shivered, swelled, reached forth, scrunched up and, in doing so, began to move across the seafloor, leaving a trail behind it.

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this theory. Around 530 million years ago, like a symphony warming up, the fossil record began teeming with a cacophony of different fossil types. Further back than that was nothing: silence. Some scientists, like Roderick Murchison, a geologist and devout Christian, believed that this lack of evidence was geologic proof of a biblical genesis. (“And God said, ‘Let the water teem with living creatures ...’ ”) Charles Darwin cautioned against this interpretation, writing in On the Origin of Species that, “We should not forget that only a small portion of the world is known with accuracy.” He saw the entire geologic record as a history book stretching across multiple volumes. “Of this history we possess the last volume alone, relating only to two or three countries,” he wrote. “Of this volume, only here and there a short chapter has been preserved; and of each page, only here and there a few lines.” The truth, it now seems clear, is that Precambrian animals had existed in great numbers but, being soft-bodied, had not lent themselves to fossilization. They crop up exceedingly rarely, in places like Mistaken Point, where the geologic conditions were just right.

CONQUERORS AND DEMONS Liu’s plan was to begin our tour at a prominent fossil site called Pigeon Cove, and then work our way forward in time, covering about 10 miles on foot and by car. We would visit each of the area’s most impressive fossil beds, culminating at the surface where Liu had discovered the fossil trails.

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during a class in his second year at Oxford with a professor named Martin Brasier, who spoke inspiringly about the mysteries of Precambrian fossils. Brasier — who died in a car accident in 2014, at the age of 67 — was a Shiva-like igure among Ediacaran paleontologists, slashing down flimsy theories and widening the domain of that which cannot be deinitively stated. In his 2009 book, Darwin’s Lost World, Brasier briskly disassembled the principle of uniformity, which broadly says that, natural laws being uniform, fossils can be best understood by studying living animals. Uniformitarianism has proved a powerful tool in many ields, Brasier admitted, but it ignores an organism’s profound interdependence with its environment. The theory breaks down in the Precambrian era, when the oceanic ecosystem was radically different. “The world before the Cambrian was, arguably, more like a distant planet,” Brasier wrote. To us land dwellers, even the present-day deep sea is foreign, a crushing black space haunted by spectral oddities: glass squids, carnivorous jellyish, a fever dream of fluorescence. But in the time when Ediacarans thrived, the oceans were stranger still. The irst Ediacaran to begin crawling around would have discovered a world devoid of predatory animals, with a seafloor covered either in thick bacterial mats or toxic sediment and, possibly, a climate thawing from a worldwide glaciation event known as “Snowball Earth.” If that pioneering Ediacaran could see, it would have discovered an underwater desert patchily carpeted with gelatin. Here and there it may have spotted other, nonmobile Ediacarans, which resembled fleshy leaves, many-tendriled sea anemones or low, round blobs: a whole world populated by brainless, jellyquivering do-nothings. The mystery Liu was trying to unravel — regarding the origins of animal movement — is central to solving the larger mystery of how that alien planet transformed into the natural world we all know. Muscular locomotion could have allowed animals to graze on the beefsteak-like bacterial mats and to attack other stationary organisms. The invention of violence might then have kicked off a biological arms race, prompting organisms to evolve hard shells and sharp teeth, the shields and swords that characterize the Cambrian fossil record. This hardening of animal bodies eventually led to the rise of trilobites and tyrannosaurs and Eocene-era Egyptian elephants — and us. Before the discovery of Ediacaran fossils, and even for a while afterward, many prominent scientists argued that complex life began at the dawn of the Cambrian Period. Looked at from a certain angle, the fossil record seemed to support

Paleontologists gather around fossil traces left by some of the first creatures to move themselves across Earth’s surface.

a fungus,” Matthews said. “They’re actually biologically really close, but they just ‘decide’ to stick their cells together slightly differently. And just because one evolved to stick its cells together differently than another, one mainly just grows on dead trees, and the other has conquered the Earth.” What, then, makes a conqueror? We have sex. We eat life, not sunlight. We contain multiple cells, which, in turn, contain nuclei, but lack rigid walls. And, in almost every case, we grow muscles. Muscles, I learned, are a crucial component of Liu’s big question. While many kinds of organisms (even single-celled ones) can swim, reach, float, squirm and even roll, only animals have developed muscle iber, which has allowed us to move in a wider variety of ways and heave around vastly more weight. Liu’s trails, then, could help unravel the question of when animal life began. Because if something was big and strong enough to create those trails 565 million years ago, it must have had muscles, which means it must have been an animal. In a neat coincidence, the same summer Liu discovered the fossil trails, he also unearthed a brand-new Ediacaran species with noticeable muscle ibers — at 560 million years old, by far the earliest muscles in the fossil record. While he doesn’t believe it was responsible for making the trails, it does provide evidence that musculature was developed earlier than anyone had previously thought. The new species was a ghastly looking thing, a webbed, cupped hand reaching up from a slender stalk, as if waiting to trap a passing foot. Liu named it Haootia quadriformis, drawing from the language of the island’s indigenous inhabitants, the Beothuk. Haoot means, simply, “demon.”

HOMEWARD BOUND Our rise through geologic time ended at the bedding plane that bore Liu’s fossil trails. On a rock wall facing the sea there protruded a waisthigh shelf. We hovered over the shelf, looking down. Once again, I saw only a flat expanse of

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TOP: RUTH SCHOWALTER. BOTTOM: JACK MATTHEWS/UNIVERSITY OF OXFORD

Liu examines fossils at Mistaken Point by creating a string grid on the rock surface. More than half a billion years ago, this site held a seafloor ecosystem teeming with strange life forms.

Windows open to the hard sea wind, we raced across a landscape of stooped trees and yellowing grass to Pigeon Cove, where we got out and hiked down a dirt path to the seaside. There lay a flat slab of rock, the size and texture of three cracked concrete tennis courts, which sloped down into the sea. Its surface was a swirl of gray, chalkboard green and dusty eggplant. Impressed into it were faint but distinct symbols. One looked like a fleshy frond. Another looked like an arrowhead, but in life probably resembled one of those conical corn snacks sold at gas stations, with its narrow end stuck into the ground. A third, which paleontologists call a “pizza disc,” was just a big, bubbly mess. A few hours later, we made our way over to the area’s most famous fossil bed, the blandly named E Surface, which cantilevers out high over the ocean. Before we stepped out onto the bedding plane, we removed our shoes and put on polyester booties to protect the fossils from erosion. The Pigeon Cove surface had held about 50 fossils; E Surface held 4,000. They were everywhere, a vast fossilized garden of fronds and blobs and spirals, some bigger than a large hand. Of course, it was not an actual garden; plants would not appear in the fossil record for another 200 million years. For some reason, I was stuck on this point. They looked like plants, I kept saying. Oxford postdoc Jack Matthews, the youngest member of Liu’s research group, explained that this was because, this far in the past, the lines between the kingdoms grow fuzzy. We, and every organism currently living on Earth, he said, are at the crown of the tree of life. Down at the base of the tree lie the very irst single-celled organisms, from which everything else sprang. So the further down the trunk of the evolutionary tree you look, the more organisms resemble one another. “That’s when you get into the nitty-gritty deinitions of what deines, say, an animal and

ALEX LIU

stone until Liu pointed out the trails subtly etched into the rock. Here, inally, was what I had come to see: the world’s oldest trails. They were easy to miss; it looked as if someone had lightly dragged a pencil eraser through drying concrete. Matthews opened his canteen and poured some water over the rock, so the trails would stand out in starker relief. Even still, I came to understand how dozens of other paleontologists had failed to notice them. All around were large, distinct body fossils impressed into grand sweeping surfaces. Liu’s trails were like a poem carved onto a handrail in a stairway of the Louvre. We worked our way along the shelf, inspecting yet more trails. Some were larger than others, but none was wider than a thumbprint. Most were relatively straight, but one peculiar trail looped back on itself, like a snake in agony. Liu believed that it provided further evidence that the marks were not, as some had argued, produced by a rock or shell being dragged by a current along the seafloor. I lightly ran my ingers over the trails. They bore the distinct texture of life. Their surface was

These trace fossils hold evidence of Earth’s earliest known muscles, which ultimately led to an evolutionary explosion.

(Tribrachidium)

patterned with a series of nesting arcs that looked like repeating parentheses: ((((((( Liu thinks each arc was made by the creature’s circular foot as it inflated with water and extended forward, smearing the front edge of the previous impression. At the end of some of the trails was a small dimple called a “terminal impression,” which might indicate the organism’s inal resting place. Modern sea anemones creep along the seafloor using a similar system of hydrostatic inflation. And this, Liu thought, could provide a clue as to why the irst animals made trails. Many of the Ediacarans found on Mistaken Point were believed to have lived their lives secured to the ground by suction cup-like feet, with their fleshy bodies extending out into the water column to gather food. Modern animals with similar body types typically prefer to latch on to a hard substrate, like stone or, when available, glass. In his lab, Liu had observed that when sea anemones were forcefully pried loose from the aquarium’s glass, they would creep across the tank’s sandy bottom until they encountered another hard, flat surface. Liu’s best guess was that his fossil trails were similarly formed: An Ediacaran was washed from its rock and, mired in loose sediment, struggled through the muck to regain its perch. I had come to Mistaken Point hoping to gain some understanding of why the irst animals began to roam. I would have assumed the trail-maker was propelled either by food, sex or imminent danger. I hadn’t accounted for this counterintuitive but perhaps equally primal need: the desire for stability. There is no sure way of knowing what the ancient Ediacarans felt, or if they even could feel. But here, written in stone, was a clue. In the end — or rather, in the beginning — the irst animals to summon the strength to venture forth may simply have wanted to go back home. D

From ON TRAILS: AN EXPLORATION by Robert Moor. Copyright © 2016 by Robert Moor. Reprinted by permission of Simon & Schuster, Inc.

Origin Story

Trading Places Long before the Silk Road or the Roman Empire, the Indian Ocean was awash with commerce. BY ADRIANNE DAGGETT ADDITIONAL REPORTING BY GEMMA TARLACH

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An early 20th century painting captures a dhow sailing along the East African coast. These traditional boats plied the waters of the Indian Ocean for millennia, connecting continents.

During its peak, the trade network connected places as far-flung as China, Rome and southern African kingdoms such as Great Zimbabwe. of earlier regional networks. By 3000 B.C., travelers in small canoes and rafts moved between towns and trading ports along coastlines from Arabia to the Indian subcontinent. By 2000 B.C., millet and sorghum — grains imported from the East African coast — were part of the cuisine of the Harappan civilization, which stretched across today’s Pakistan and northern India. Archaeological evidence and genetic studies suggest that the irst major settlement of Madagascar came not from Africa — a short hop across the Mozambique Channel — but from Indonesia, 4,000 miles away.

During its peak, the trade network connected places as far-flung as China, Rome and southern African kingdoms such as Great Zimbabwe. In terms of the sheer amount of goods moved, the maritime trading system rivaled its more famous inland relative, the Silk Road. A irst-century Greek manuscript, The Periplus of the Erythraean Sea, recorded trading depots and ports’ locations, goods and populations with enough accuracy that researchers today are able to match archaeological sites with the text’s descriptions. For example, using the text, one team has determined a site in present-day Eritrea was Adulis, an important city in the early Christian empire of Aksum. For more than a millennium, farmers, shepherds and merchants went there from surrounding villages to exchange raw materials such as ivory, salt and animal skins for Persian glassware, Arabian spices and other exotic products. Many of these goods made their way far inland. Archaeologists today regularly recover small items like glass beads, spindle whorls or Chinese

TOP: MARY EVANS PICTURE LIBRARY. BOTTOM: LCSWART/SHUTTERSTOCK

It’s a chapter of history nearly forgotten: Intrepid merchants and explorers traveled thousands of miles, not along storied caravan routes, but across the great blue expanse of the Indian Ocean, exchanging goods and ideas, forming bonds and challenging our notions about the ancient world. “People think that it must have taken a long time to get anywhere, that it must have been dificult to travel long distances, but that is not true,” says archaeologist Marilee Wood, whose research focuses on the network’s glass bead trade. “This [ield of study] is about opening that all up.” In fact, by the time Marco Polo set out to explore East Asia in the 13th century, communities across Africa, Asia and the Mediterranean had been exchanging their wares for thousands of years in a vast network driven by the monsoon winds of the Indian Ocean. Early scholars presumed that the Indian Ocean network had developed to supply the Roman Empire’s demand for exotic goods. However, new evidence shows that the network predates the Romans by generations. The Indian Ocean system developed out of the gradual The ancient grain millet. integration

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4 Researchers found Ming Dynasty porcelain from China among artifacts of Great Zimbabwe, capital city of a massive southern African kingdom.

8 Rhapta

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4 56

Not only owning, but also giving away such exotic items appears to have been critical in gaining political power and building trust.

MOVERS AND SHAPERS Archaeologists still have many questions about the Indian Ocean exchange network. Tracing the movement of goods from place to place is relatively easy. With pottery, for example, members of a single community tend to repeat the same decorative styles over time. 5 Many types of Stone, clay and other glass beads found raw materials, used in Africa, such as garden roller to produce objects beads (left) and ranging from anchors Mapungubwe Oblate beads to gold bullion, (right), were made have unique thousands of miles chemical away, in Europe and Asia.

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Southwest monsoon, May – October Established trade routes ca. 1st to 3rd century AD

signatures that vary by geographic location and can be traced back to their source. Figuring out how the goods were moved is a little harder. Ships are rare inds, and inland caravans even rarer. One thing scholars know for certain is that the very nature of the ocean trade made prolonged periods of interaction necessary: The currents of the Indian Ocean change seasonally, and traders had to wait for months until currents shifted in favor of the return voyage. For many seafarers, these foreign ports became a second home. However, outside of the ports mentioned in a handful of ancient texts, it’s unclear just how merchants, and their goods, traveled inland. Keilwe Rammutloa, a graduate student at the University of Pretoria,

MAP: RICK JOHNSON/DISCOVER. FROM TOP: DAVID STANLEY/CREATIVE COMMONS 2.0; GRANGER, NYC; DEA/A. DAGLI ORTI/DE AGOSTINI/GETTY IMAGES; SHADRECK CHIRIKURE, S. AFR ARCHAEOL REVIEW (2014) 31: 705. DOI:10.1007/S10437-014-9171-6; MARILEE WOOD (2)

2 This bust of a “priest king” from the Indus Valley site of Mohenjo-Daro is about 4,000 years old. Its carver may have eaten millet imported from Africa via the Indian Ocean trade network.

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3 The Persian daric, a gold coin minted in Asia Minor, was widely used in trade about 2,500 years ago.

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1 As trade flourished along the network’s routes, so did construction, such as this massive fifth-century basilica in Adulis, a port city in what’s now Eritrea on the Red Sea coast.

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Less famous than the Silk Road — its land-based parallel — the maritime web of commerce and cultural exchange operated on seasonal monsoon winds. The network grew out of ancient regional routes and, by 2,000 years ago, connected Western Europe with East Asia.

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6 This exquisite gold rhino is one of many grave goods from burials at the site of Mapungubwe in southern Africa. In the 12th and 13th centuries, the city was a nexus for local, inland commerce and Indian Ocean gold trade.

7 Glass beads, filling a clay cup found in southern India, served as currency along some maritime and inland routes associated with the Indian Ocean trade network.

8 Modern tourists walk in the footsteps of traders and sailors who, a thousand years ago, stopped to worship at the Great Mosque of Kilwa Kisiwani, on Africa’s east coast.

9 On the Indonesian island of Sumatra, a hoard of Chinese coins found in a river estuary attest to regional commerce routes combining to create the greater Indian Ocean network.

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CLOCKWISE FROM TOP LEFT: STEFAN HEUNIS/AFP/GETTY IMAGES; DEA/G. DAGLI ORTI/GRANGER, NYC; REYNOLD SUMAYKU/ALAMY STOCK PHOTO; MARILEE WOOD

SOURCE: PHILIPPE BEAUJARD

is building a database to trace the distribution of exotic goods at sites across southeastern Africa. She’s inding evidence that suggests members of indigenous communities exchanged these items, often as gifts, rather than professional merchants establishing trade between towns. Like Wood, Rammutloa has uncovered a social aspect to the items. Mapungubwe, for example, the irst indigenous kingdom of southern Africa, was rich in ivory and gold — but bodies found in its cemeteries were interred with glass beads from Persia and porcelain from China. “People used the materials to create relationships,” says Rammutloa. “We’re talking about humans here. Someone gives you a gift, they’re negotiating a role in your life. It creates a network.”

Indian Ocean trade never truly disappeared. Beginning in the 15th century, however, with the expansion of European exploration and China’s withdrawal from international affairs, the world’s economic focus shifted westward. In the centuries that followed, few researchers studied this early and extensive trade network. Says Wood: “It’s the European background of the people writing the histories, including our own. There’s more work being done now, but part of the problem is that we depend on written documents, and there are a lot less [for the Indian Ocean trade network]. It’s also a question of language. I’m sure there are a wealth of documents on it hidden away in China, but someone’s got to translate them.”

Other forces, from unstable governments to international sanctions, have also stymied research in the past. “The political past of South Africa has left a huge gap,” says Rammutloa. “It’s only now, after apartheid, that we’re able to get involved in international projects.” Over the past decade, dozens of regional research programs have developed in coastal Africa, and connected with peers in Europe and Asia, in a way re-creating the trade routes they study. Only now they’re exchanging information rather than goods. D Adrianne Daggett received her Ph.D. in anthropology from Michigan State University and currently works for the South Carolina State Historic Preservation Office.

November 2016 DISCOVER

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Prognosis

The Heart of Mississippi Environment? Genetics? Why does heart disease strike so many more African-Americans? BY JEFF WHEELWRIGHT

When you hear that Mississippi is a red state, you think politics, but red also applies to the toll of its cardiovascular disease. Look at the Centers for Disease Control and Prevention’s map of the death rates from heart disease down to the county level across the U.S. Colors range from a healthy pale pink to deep red — those areas are the sickest. Mississippi is bathed almost entirely in crimson. Among Americans 35 and older, Mississippians have the highest mortality from heart disease in the nation, ranging between 450 and 850 deaths per 100,000.

By no coincidence, this state also has the greatest portion of AfricanAmerican residents, close to 40 percent of the total population. Ervin Fox, a Harvard-trained cardiologist and epidemiologist, knows these statistics from multiple perspectives. Fox, 49, grew up in the Mississippi Delta region, where the soil is rich and cotton was king. He treats patients at the University of Mississippi Medical Center (UMMC)

Heart Disease Death Rates, 2011–2013 Adults, Ages 35+, by County

Mississippi has the the nation’s highest mortality rate from heart disease. DATA SOURCES: NATIONAL VITAL STATISTICS SYSTEM; NATIONAL CENTER FOR HEALTH STATISTICS

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Age-Adjusted Average Annual Rates Per 100,000 103.6 – 291.0 291.1 – 334.6 334.7 – 373.9 374.0 – 427.5 427.6 – 1094.1 Insuficient Data

in Jackson, and he also does research for the Jackson Heart Study, the African-American version of the older, more famous ongoing Framingham Heart Study. Since 1948, thanks to thousands of health histories collected from the mainly white residents of Framingham, Mass., epidemiologists have learned how blood pressure, smoking habits, cholesterol and a few other quantiiable factors can forecast heart disease and stroke, two general conditions comprising cardiovascular disease (CVD). The Jackson study, starting in 2000, was meant to determine if the same variables applied in the same way to black people. The same factors do apply, says Fox, but the weighting of them is different, and the outcomes are worse. African-Americans die disproportionately from CVD. If you are black,

Ervin Fox (left) treats patients at the University of Mississippi Medical Center. He also conducts research for the Jackson Heart Study, directed by Adolfo Correa (right).

CLOCKWISE FROM TOP: JPC-PROD/SHUTTERSTOCK; UMMC PUBLIC AFFAIRS; MEGAN BEAN/MISSISSIPPI STATE UNIVERSITY. MAP: CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC)

→

U.S. Stroke Death Rates, 2010

U.S. Incidence of Heart Attack or Fatal Coronary Heart Disease, 2005–2010

60

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ALISON MACKEY/DISCOVER AFTER HEALTH DISEASE AND STROKE STATISTICS – 2014 UPDATE: A REPORT FOR THE AMERICAN HEART ASSOCIATION

DATA SOURCES: NATIONAL CENTER FOR HEALTH STATISTICS; NATIONAL HEART, LUNG, AND BLOOD INSTITUTE

your risk of having a stroke is twice that of a white person, and your relative risk of dying from that stroke is even higher. Although life expectancy for both blacks and whites has improved in recent decades because of better awareness of CVD risk factors and better treatments, the gains have been greatest among whites — and black progress has slowed or stopped. It’s almost a truism in medicine that men have more heart disease than women. “Yet today,” Fox tells me, “CVD in black women is as high as in non-Hispanic white males. Deaths in African-American women exceed those of white males.” He gives a grim chuckle. “It’s so bad it’s almost something to laugh at. Is it environmental, or genetic, or related to [public health] funding? The Jackson Heart Study was established to help answer these questions.”

ENVIRONMENT VS. GENETICS Some 5,300 people from Mississippi, who ranged in age from 21 to 84, signed up for the study, the largest enrollment ever of African-Americans in a research project. About 70 percent of the group is still being monitored 16 years later. Their health picture relative to whites’ starts to head south when they reach 45

African-Americans die disproportionately from CVD. If you are black, your risk of having a stroke is twice that of a white person, and your relative risk of dying from that stroke is even higher. or 50. “That’s the most productive time of life,” Fox observes, “and that’s when the disparity in blacks goes up to three times as high for cardiovascular events like heart attacks and strokes.” Fox had named two biological actors, the environment and genetics, which oppose each other like feuding siblings yet often ind themselves interacting. I ask the Jackson study director, Adolfo Correa, which one he thought was the more influential in creating the health disparity. Was it blacks’ and whites’ subtle genetic differences? Or were the social, environmental and behavioral factors of health — smoking, diet,

access to care, psychological distress, racism — more powerful? Stress, too, makes patients’ blood pressure rise, at least temporarily, the Jackson studies have found. “The answer to that,” says Correa, “depends on the objective. If you want to change the risk proile of people, you need to work on the environment. The one thing you can work on is the environment.” He went on to describe efforts to educate Mississippians in healthier living. “But also you need to understand the genetics.” Correa points me to a gene known as APOL1. In Africa, those who have two speciic variants of the gene gain some protection against sleeping sickness, which is caused by an environmental parasite. But APOL1 carriers living in the U.S. are more susceptible to CVD and chronic kidney disease. The inding stems from an analysis of 1,959 participants in the Jackson Heart Study. While Mississippi has no sleeping sickness, it does have lifestyle factors leading to obesity, hypertension and diabetes, which damage the heart and kidneys. The Delta thus may host an unfavorable synergy between evolutiondriven DNA and the 21st century environment. Similarly, carriers in the

November 2016 DISCOVER

65

Jackson study of one copy of the genes that cause sickle-cell disease — a useful trait against malaria in Africa — appear to be more at risk for kidney disease.

READING THE HEART Overall, scientists have linked dozens of genes to cardiovascular conditions, but organizing the indings by race or ethnicity has barely started. Take, for example, a condition called cardiac hypertrophy, in which the left ventricle, one of the two major chambers of the heart, increases in size and thickness, usually in concert with weight gain and hypertension. Hypertrophy raises the risk of heart attacks and strokes, and it affects African-Americans more frequently than whites. But the relationships between the moving parts — race, blood pressure, obesity, enlarged heart mass and bad outcomes — haven’t been clear. Fox’s specialty is to read echocardiograms, basically ultrasound movies of beating hearts. The sound waves pass through the muscle walls and provide a gauge of left ventricular mass (LVM). Some 5,300 Jackson study participants took two echocardiograms, eight years apart. In succeeding years, as the group on the whole put on weight and grew hypertensive, there came an unfortunate

Normal heart

Right ventricle

Cardiac hypertrophy

Left ventricle

Enlarged left ventricle

Hypertrophy raises the risk of heart attacks and strokes, and it afects African-Americans more frequently than whites. But the relationships between the moving parts — race, blood pressure, obesity, enlarged heart mass and bad outcomes — haven’t been clear.

Jackson Heart Study researcher and cardiologist Ervin Fox watches as Shari Cook (foreground) and Audrey Samuels take readings from a woman participating in the Mississippi heart study.

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cascade of “events” such as heart attacks, heart failure, strokes, arterial blockage and chest pain. As lead author on a 2015 paper, Fox described the mathematical correlation between body mass index, blood pressure and ventricular mass during the initial phase of the study. Later in life, those who had shown the greatest change in their LVM were more likely to experience a cardiac event. With LVM on the radar screen, investigators funded by the American Heart Association are looking at genes that control the growth of the heart. Normally the genes shut off in adulthood, but they appear to start up again in CVD patients. Investigators will check the stored samples of the Jackson population for a particular DNA pattern, then check for the pattern in the Framingham population as well. If the LVM growth mechanism for blacks isn’t the same as for Caucasians, this might be another window into the health disparity. Although aging isn’t talked about much in cardiovascular research, age of course is an important risk factor for CVD. The initial Jackson cohort included many who were over 65, and that was 16 years ago. When does normal mortality, I ask Fox, interfere with studies of abnormal mortality? Shouldn’t the focus shift to the sons and daughters of participants, as in Framingham? “People are living longer,” he replies. “It’s good to follow the disease in aging. But technology has changed, our awareness of risk factors has changed, medications have changed. Yes, it would be great to follow a young cohort, growing up in the current environment and strategies in medicine, and see how they do.” If funding from the National Institutes of Health is renewed in 2018, the Jackson Heart Study hopes to enlist another generation. D Jeff Wheelwright is a contributing editor at Discover.

TOP: MONICA SCHROEDER/SCIENCE SOURCE. BOTTOM: UMMC PUBLIC AFFAIRS

Prognosis

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History Lessons

The Missing Moon Files Researchers scour old labs and archives, looking for invaluable lunar data before it’s too late.

→

Seiichi Nagihara began to sweat too late. The last scientists who worked as he dug through long-forgotten on the Apollo missions are aging fast, boxes in a cluttered basement as are the fragile magnetic tapes on storeroom at a Columbia University which the data were recorded and the outpost in Palisades, N.Y. But the trim machines that can read them. 54-year-old kept working. It was June Nagihara’s motivation to ind the 2013, and he had come all the way information is simple: We’re not going from Texas to search for decades-old back to the moon anytime soon. clues about the moon. “Until then,” he says, “that’s the only Nagihara pawed through the dataset we’ve got.” yellowing iles of Marcus Langseth, a Columbia geologist who died in 1997. Between the late 1960s and mid ’70s, Langseth was in charge of a project to study how heat escaped from the moon’s interior, using sensors deployed by astronauts during the Apollo missions. This experiment was just one part of the Apollo Lunar Surface Experiments Package (ALSEP), the only comprehensive set of moon-based studies humans have ever conducted. Nagihara, a geophysicist at Texas Tech University, hoped to reanalyze Langseth’s heat data with modern analytical techniques on computers that scientists back then could only dream of. But as much as half of the ALSEP data had gone missing since Congress Apollo 15 astronaut James Irwin (above), pulled the plug on the helped deploy an project’s funding in 1977. Apollo Lunar Surface Experiments Package Now, Nagihara and (ALSEP) dust scanner a band of researchers(bottom). Alan Bean of Apollo 12 deploys turned-detectives are one of the first ALSEP racing to recover the experiments (top right), a kind of ion detector. lost data before it’s

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DATA ACQUISITION Apollo 12 astronauts Charles “Pete” Conrad and Alan Bean installed the irst set of ALSEP instruments on the moon in 1969. More followed on every mission (except Apollo 13), until the inal moon landing in 1972. This equipment monitored the moon’s meager atmosphere, listened for the faint rumbles of moonquakes and asteroid impacts and measured lunar

PROJECT APOLLO ARCHIVE/NASA; BACKGROUND: VALENTIN AGAPOV/SHUTTERSTOCK

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History Lessons

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Marcus

The technology used to handle ALSEP data now seems ancient. Computer rooms (above) would store data on actual tapes, such as this seven-track, half-inch-wide reel (right). Yet that data, like the seismic plot (far right), can still lead to new lunar insights.

he last scientists who worked on the Apollo missions are aging fast, as are the fragile magnetic tapes on which the data were recorded and the machines that can read them. as NASA was running out of money, researchers at the University of Texas at Galveston — where Nakamura worked at the time — took over the task of producing archival tapes. These remained at the university after ALSEP ended, although some thought they didn’t hold much value, Nakamura says. “Some people were saying, ‘Those are old data, they are of no use.’ ” Nakamura disagreed; he foresaw a day when future researchers could unlock new insights in the old data.

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So, in the early 1990s, he sought support from NASA to preserve the tapes he saved from Galveston. NASA, again citing a tight budget, turned him down, but the Japanese Aerospace Exploration Agency eventually gave Nakamura a grant to condense about 9,000 tapes into just 80 cassettes. These data, which include a full record of the passive seismic experiments as well as everything from the last 19 months of the project, remain the most complete record of raw ALSEP data in existence.

MOON-SHAKING FINDINGS Without seeing the missing data, it’s impossible to say how valuable they might be. But the ALSEP data we do have offer some hints. When lunar seismic data were irst collected and analyzed in the 1970s, researchers like Nakamura interpreted them by eye, holding the jagged lines of seismograms over a light table. “During the mission, all we had was a big computer with 24 kilobytes of memory — a very small fraction of what you have on your cell phone,” Nakamura says. Recently, he and other researchers have reanalyzed the data with great

CLOCKWISE FROM LEFT: HAMISH LINDSAY; LAMONT-DOHERTY EARTH OBSERVATORY/COLUMBIA UNIVERSITY; NASA; YOSIO NAKAMURA

heat flow. All together, the 14 experiments operating across ive landing sites threw open a window into the workings of our lonely natural satellite. As the years wore on, some of the instruments winked out, but most outlasted their budget, and eventually the program lost support from Congress. In 1974, NASA began to dismantle ALSEP’s network of scientists and engineers, and in 1977, the agency shut down the range stations that received radio data from the lunar instruments. After the project ended, much of the data got lost despite preservation efforts. For every experiment, NASA made copies of the data: The agency kept one version and sent the other to project scientists like Langseth. Most of the surviving ALSEP data comes from researchers, who processed the raw data and archived the results with NASA. However, many of these records end in 1974 and are often incomplete. Langseth’s contribution, for example, contained only what he needed for his work — one out of every seven measurements collected by the heat flow sensors, and no raw data. That was ine, in principle, because NASA had backup copies of everything. However, scientists now cannot ind most of these archival tapes. NASA records show they were sent to the National Archives, but the space agency withdrew most of them again in 1980. That’s where the paper trail ends. Yosio Nakamura, a retired geophysicist at the University of Texas at Austin who worked on ALSEP’s seismic experiments, suspects NASA recalled them for possible reuse during a tape shortage, then lost track of them. Fortunately, data from the inal years of the project survived intact, thanks largely to Nakamura. In 1976,

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TIME’S CHANGES Because no one has returned to the moon since the Apollo program, many young researchers like Weber began to seek out data for the other ALSEP experiments, only to realize how much was missing. But nobody made a serious effort to igure out what happened, or ind the tapes, until Nagihara stumbled onto the mystery while searching for Langseth’s raw heat-flow data.

Because no one has returned to the moon since the Apollo program, many young researchers began to seek out ALSEP data, only to realize how much was missing. Fueled by curiosity and concern, he and two dozen other scientists oficially formed the ALSEP Data Recovery Focus Group in 2010. NASA gave the group, chaired by Nagihara, its blessing and provided funds to help the team hunt down and archive the lost tapes, as well as make the existing ALSEP data more accessible to today’s researchers. The recovery effort got off to a promising start. Just months after the group formed, Pamela Baker at the Johnson Space Center Records Ofice found paperwork that led to the discovery of 450 tapes at a national records center in Maryland. When

Nagihara went to collect them, he was delighted to ind that they were archival tapes containing a full record of ALSEP data for a three-month period in the spring of 1975. But then the trail went cold. With no leads on the remaining 4,550 archival tapes, Nagihara tried to ind some of the tapes NASA had sent to the project scientists for analysis — like the ones containing Langseth’s heat data — in hopes that they hadn’t been thrown out. In addition to that dusty Columbia basement, he also visited the University of Maryland to scour the records of the late physicist Joseph Weber, who oversaw ALSEP’s gravimetry experiments. Although he found some useful documentation, neither of those visits yielded any tapes. A recent tip from NASA’s Astromaterials Acquisition and Curation Ofice also proved to be a false alarm. Now, Nagihara fears that time is running out. The tapes themselves are quickly degrading, as is the archaic equipment needed to extract the data. “If we ind more tapes 10 years from now,” he says, “we may not be able to read them. The clock is ticking.” D Julia Rosen is a freelance journalist in Portland, Ore.

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Apollo 12 astronaut Alan Bean carries two ALSEP packages on the lunar surface (left). A different ALSEP experiment, this time from Apollo 16 (above), measures seismic waves on the lunar surface: moonquakes.

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Seiich Nagiha i ra

FROM LEFT: COURTESY OF YOSIO NAKAMURA; PROJECT APOLLO ARCHIVE/NASA (2); JEFFREY LATKA

success. One of those researchers, Renee Weber, a lunar and planetary scientist at NASA’s Marshall Space Flight Center, detected hundreds of new moonquakes in the old data. She and her colleagues then studied how these quakes reverberated through the moon’s interior to probe its structure. In 2011, they published a paper in Science presenting a new look at the moon’s core. Weber thinks more discoveries will follow as scientists bring increasingly sophisticated analytical techniques to bear on the ALSEP data. “It’s invaluable,” she says.

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The Thulean Route land bridge once connected North America with Eurasia; remnants are still visible on the seafloor today (top). The Kazarma bridge in Greece (above) may be the world’s oldest man-made bridge still in use.

BY GEMMA TARLACH

1 The most important bridges on Earth have nothing to do with engineers and masons: Through the ages, land bridges have allowed species to reach new territories. Some are better known than others. Ever heard of the Thulean Route? 2 Also known as the North American Land Bridge (NALB), the volcanic Thulean plateau arose around 56 million years ago. It stretched from Greenland to the British Isles, connecting North America with Eurasia. 3 While we often think of land bridges as animal migration highways, they also help plants disperse. A 2013 study found the NALB allowed hickory, native to northeastern North America, to spread to Europe and Asia. 4 Recent genetic studies have conirmed the irst humans to arrive in the Americas traveled via Beringia. The land bridge connected Siberia and North America beginning 38,000 years ago, during the Last Glacial Maximum. 5 Beringia was probably at its greatest size 20,000 years ago, when sea levels were as much as 400 feet lower than they are today. Within 9,000 years of its peak, however, the last dry bits of Beringia slipped beneath the waves. 6 Beringia will rise again! Well, maybe. The land bridge has appeared periodically for the past 70 million years during times of extensive glaciation. 7 Before it was sliced open by a shipping canal in 1914, the Isthmus of Panama united a land mass stretching from the Arctic Circle to subantarctic southern Patagonia. Not united: researchers debating how long the land bridge was around. A 2015 study in Science claims at least 13 million years, but a paper published in August says no more than 3 million. 8 When it comes to bridges we’ve built, even the most elaborate can be reduced to two components: supports and a deck. Among the basic bridge types (beam, arch, truss and suspension), the simplest is the beam. It’s a single deck across two supports, like a plank across a stream. 9 In addition to load — the weight of the deck and whatever is crossing the bridge — engineers worry about the forces of compression and tension. 10 Think about standing at the center of that plank

crossing the stream. The plank bows downward from your weight; the top of the plank shortens (compression) while the underside stretches (tension). Too much of either creates a weak area that could leave you all wet. 11 Want to stabilize your beam bridge? Try adding trusses. The triangular supports, a common feature of shorter-span railway bridges, give the deck greater rigidity, which dissipates, or distributes, both compression and tension forces. 12 For longer spans, engineers may turn to suspension bridges. The deck is suspended by cables (stretched with tension), which hang from towers (compressed into the ground). 13 Arch bridges, popular since antiquity, are more stable than the beam variety. The entire bridge is under compression, which is dissipated out and down from the center — right into the supports. 14 Bridges need to be stable, but bridges themselves can also provide stability. Disulide bridges, for example, hold together the different protein chains that make up an antibody. You can think of them as the glue in immunoglobulin molecules, the warriors of the immune system. 15 A different bridge keeps people glued to their seats: the card game. Today’s Bridge evolved from earlier games such as Whist. Some of its predecessors date to the 16th century. 16 The game’s name is an Anglicization of the word biritch, which some historians believe has Russian origins. Its roots may be in Turkey, however, where it was a popular diversion among expats, including Russians, nearly two centuries ago. 17 Some bridges still in use today have even older roots. The sturdily built Pons Fabricius arch bridge has connected Tiber Island to the heart of Rome since 62 B.C. 18 You can thank those industrious Romans for building the world’s oldest reliably dated bridge, too: They erected a stone arch span over the Meles River in Izmir, Turkey, in the ninth century B.C. 19 The Meles bridge is used even now, as is the Kazarma, or Arkadiko, bridge in southern Greece. Built from unworked limestone boulders and rocks, the basic arch, though never conclusively dated, may be from the 14th century B.C. 20 Can’t credit the Romans with this one, though. The 22-meter-long Kazarma is an example of Mycenaean Bronze Age masonry. In your face, Romans! D Gemma Tarlach is a senior editor at Discover.

DISCOVER (ISSN 0274-7529, USPS# 555-190) is published monthly, except for combined issues in January/February and July/August. Vol. 37, no. 9. Published by Kalmbach Publishing Co., 21027 Crossroads Circle, P.O. Box 1612, Waukesha, WI 53187-1612. Periodical postage paid at Waukesha, WI, and at additional mailing offices. POSTMASTER: Send address changes to DISCOVER, P.O. Box 62320, Tampa, FL 33662-2320. Canada Publication Agreement # 40010760. Back issues available. All rights reserved. Nothing herein contained may be reproduced without written permission of Kalmbach Publishing Co., 21027 Crossroads Circle, P.O. Box 1612, Waukesha, WI 53187-1612. Printed in the U.S.A.

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