Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen

by Christopher McDougall

  “That’s what led me, like others, to dismiss the idea that humans evolved as running animals,” Bramble said. “And I would have bought into the story and remained a skeptic, if I hadn’t also been trained in paleontology.”

  Dr. Bramble’s secondary expertise in fossils allowed him to compare how the human blueprint had been modified over the millennia and check it against other designs. Right off the bat, he began finding things that didn’t fit. “Instead of looking at the conventional list, like most morphologists, and ticking off the things I expected to see, I began focusing on the abnormalities,” Bramble said. “In other words, what’s there that shouldn’t be there?” He began by splitting the animal kingdom into two categories: runners and walkers. Runners include horses and dogs; walkers are pigs and chimps. If humans were designed to walk most of the time and run only in emergencies, our mechanical parts should match up pretty closely to those of other walkers.

  Common chimps were the perfect place to start. Not only are they a classic example of the walking animal, but they’re also our closest living relative; after more than six million years of separate evolution, we still share 95 percent of our DNA sequence with chimps. But what we don’t share, Bramble noted, is an Achilles tendon, which connects the calf to the heel: we’ve got one, chimps don’t. We have very different feet: ours are arched, chimps’ are flat. Our toes are short and straight, which helps running, while chimps’ are long and splayed, much better for walking. And check out our butts: we’ve got a hefty gluteus maximus, chimps have virtually none. Dr. Bramble then focused on a little-known tendon behind the head known as the nuchal ligament. Chimps don’t have a nuchal ligament. Neither do pigs. Know who does? Dogs. Horses. And humans.

  Now this was perplexing. The nuchal ligament is useful only for stabilizing the head when an animal is moving fast; if you’re a walker, you don’t need one. Big butts are only necessary for running. (See for yourself: clutch your butt and walk around the room sometime. It’ll stay soft and fleshy, and only tighten up when you start to run. Your butt’s job is to prevent the momentum of your upper body from flipping you onto your face.) Likewise, the Achilles tendon serves no purpose at all in walking, which is why chimps don’t have one. Neither did Australopithecus, our semi-simian four-million-year-old ancestor; evidence of an Achilles tendon only began to appear two million years later, in Homo erectus.

  Dr. Bramble then took a closer look at the skulls and got a jolt. Holy moly! he thought. There’s something going on here. The back of the Australopithecus skull was smooth, but when he checked Homo erectus, he found a shallow groove for a nuchal ligament. A mystifying but unmistakable time line was taking shape: as the human body changed over time, it adopted key features of a running animal.

  Weird, Bramble thought. How come we acquired all this specialized running stuff, and other walkers didn’t? For a walking animal, the Achilles would just be a liability. Moving on two legs is like walking on stilts; you plant your foot, pivot your body weight over the leg, and repeat. The last thing you’d want would be stretchy, wobbly tendons right at your base of support. All an Achilles tendon does is stretch like a rubber band—

  A rubber band! Dr. Bramble felt twin surges of pride and embarrassment. Rubber bands … There he’d been, thumping his chest about not being like all those other morphologists who “tick off the things they expect to see,” when all along, he’d been just as misguided by myopia; he hadn’t even thought about the rubber-band factor. When David started talking about running, Dr. Bramble assumed he meant speed. But there are two kinds of great runners: sprinters and marathoners. Maybe human running was about going far, not fast. That would explain why our feet and legs are so dense with springy tendons—because springy tendons store and return energy, just like the rubber-band propellers on balsa-wood airplanes. The more you twist the rubber band, the farther the plane flies; likewise, the more you can stretch the tendons, the more free energy you get when that leg extends and swings back.

  And if I were going to design a long-distance running machine, Dr. Bramble thought, that’s exactly what I’d load it with—lots of rubber bands to maximize endurance. Running is really just jumping, springing from one foot to another. Tendons are irrelevant to walking, but great for energy-efficient jumping. So forget speed; maybe we were born to be the world’s greatest marathoners.

  “And you’ve got to ask yourself why only one species in the world has the urge to gather by the tens of thousands to run twenty-six miles in the heat for fun,” Dr. Bramble mused. “Recreation has its reasons.”

  Together, Dr. Bramble and David Carrier began putting their World’s Greatest Marathoner model to the test. Soon, evidence was turning up all over, even in places they weren’t looking. One of their first big discoveries came by accident when David took a horse for a jog. “We wanted to videotape a horse to see how its gait coordinated with its breathing,” Dr. Bramble says. “We needed someone to keep the gear from getting tangled, so David ran alongside it.” When they played back the tape, something seemed strange, although Bramble couldn’t figure out what it was. He had to rewind a few times before it hit him: even though David and the horse were moving at the same speed, David’s legs were moving more slowly.

  “It was astonishing,” Dr. Bramble explains. “Even though the horse has long legs and four of them, David had a longer stride.” David was in great shape for a scientist, but as a medium-height, medium-weight, middle-of-the-pack runner, he was perfectly average. That left only one explanation: as bizarre as it may seem, the average human has a longer stride than a horse. The horse looks like it’s taking giant lunges forward, but its hooves swing back before touching the ground. The result: even though biomechanically smooth human runners have short strides, they still cover more distance per step than a horse, making them more efficient. With equal amounts of gas in the tank, in other words, a human can theoretically run farther than a horse.

  But why settle for theory when you can put it to the test? Every October, a few dozen runners and riders face off in the 50- mile Man Against Horse Race in Prescott, Arizona. In 1999, a local runner named Paul Bonnet passed the lead horses on the steep climb up Mingus Mountain and never saw them again till after he’d crossed the finish line. The following year, Dennis Poolheco began a remarkable streak: he beat every man, woman, and steed for the next six years, until Paul Bonnet wrested the title back in 2006. It would take eight years before a horse finally caught up with those two and won again.

  Discoveries like these, however, were just happy little extras for the two Utah scientists as they tunneled closer to their big breakthrough. As David had suspected on the day he peered into a rabbit’s carcass and saw the history of life staring back at him, evolution seemed to be all about air; the more highly evolved the species, the better its carburetor. Take reptiles: David put lizards on a treadmill, and found they can’t even run and breathe at the same time. The best they can manage is a quick scramble before stopping to pant.

  Dr. Bramble, meanwhile, was working a little higher up the evolutionary ladder with big cats. He discovered that when many quadrupeds run, their internal organs slosh back and forth like water in a bathtub. Every time a cheetah’s front feet hit the ground, its guts slam forward into the lungs, forcing out air. When it reaches out for the next stride, its innards slide rearward, sucking air back in. Adding that extra punch to their lung power, though, comes at a cost: it limits cheetahs to just one breath per stride.

  Actually, Dr. Bramble was surprised to find that all running mammals are restricted to the same cycle of take-a-step, take-a-breath. In the entire world, he and David could only find one exception:

  You.

  “When quadrupeds run, they get stuck in a one-breath-per-locomotion cycle,” Dr. Bramble said. “But the human runners we tested never went one to one. They could pick from a number of different ratios, and generally preferred two to one.” The reason we’re free to pant to our heart’s content is the same reason you need a shower on a summe
r day: we’re the only mammals that shed most of our heat by sweating. All the pelt-covered creatures in the world cool off primarily by breathing, which locks their entire heat-regulating system to their lungs. But humans, with our millions of sweat glands, are the best air-cooled engine that evolution has ever put on the market.

  “That’s the benefit of being a naked, sweating animal,” David Carrier explains. “As long as we keep sweating, we can keep going.” A team of Harvard scientists had once verified exactly that point by sticking a rectal thermometer in a cheetah and getting it to run on a treadmill. Once its temperature hit 105 degrees, the cheetah shut down and refused to run. That’s the natural response for all running mammals; when they build up more heat in their bodies than they can puff out their mouths, they have to stop or die.

  Fantastic! Springy legs, twiggy torsos, sweat glands, hairless skin, vertical bodies that retain less sun heat—no wonder we’re the world’s greatest marathoners. But so what? Natural selection is all about two things—eating and not getting eaten—and being able to run twenty miles ain’t worth a damn if the deer disappears in the first twenty seconds and a tiger can catch you in ten. What good is endurance on a battlefield built on speed?

  That’s the question Dr. Bramble was mulling in the early ’90s when he was on sabbatical and met Dr. Dan Lieberman during a visit to Harvard. At the time, Lieberman was working on the other end of the animal Olympics; he had a pig on a treadmill and was trying to figure out why it was such a lousy runner.

  “Take a look at its head,” Bramble pointed out. “It wobbles all over the place. Pigs don’t have a nuchal ligament.”

  Lieberman’s ears perked up. As an evolutionary anthropologist, he knew that nothing on our bodies has changed as much as the shape of our skulls, or says more about who we are. Even your breakfast burrito plays a role; Lieberman’s investigations had revealed that as our diet shifted over the centuries from chewy stuff like raw roots and wild game and gave way to mushy cooked staples like spaghetti and ground beef, our faces began to shrink. Ben Franklin’s face was chunkier than yours; Caesar’s was bigger than his.

  The Harvard and Utah scientists got along right from the start, mostly because of Lieberman’s eyes: they didn’t roll when Bramble briefed him on the Running Man theory. “No one in the scientific community was willing to take it seriously,” Bramble said. “For every one paper on running, there were four thousand on walking. Whenever I’d bring it up at conferences, everyone would always say, ‘Yeah, but we’re slow.’ They were focused on speed and couldn’t understand how endurance could be an advantage.”

  Well, to be fair, Bramble hadn’t really figured that one out yet, either. As biologists, he and David Carrier could decipher how the machine was designed, but they needed an anthropologist to determine what that design could actually do. “I knew a lot about evolution and a little about locomotion,” Lieberman says. “Dennis knew a shitload about locomotion, but not so much about evolution.”

  As they traded stories and ideas, Bramble could tell that Lieberman was his kind of lab partner. Lieberman was a scientist who believed that being hands-on meant being prepared to soak them in blood. For years, Lieberman had organized a Cro-Magnon barbecue on a Harvard Yard lawn as part of his human evolution class. To demonstrate the dexterity necessary to operate primitive tools, he’d get his students to butcher a goat with sharpened stones, then cook it in a pit. As soon as the aroma of roasting goat spread and the post-butchering libations began flowing, homework turned into a house party. “It eventually evolved into a kind of bacchanalian feast,” Lieberman told the Harvard University Gazette.

  But there was an even more important reason that Lieberman was the perfect guy to tackle the Running Man mystery: the solution seemed to be linked to his specialty, the head. Everyone knew that at some point in history, early humans got access to a big supply of protein, which allowed their brains to expand like a thirsty sponge in a bucket of water. Our brains kept growing until they were seven times larger than the brains of any comparable mammal. They also sucked up an ungodly number of calories; even though our brains account for only 2 percent of our body weight, they demand 20 percent of our energy, compared with just 9 percent for chimps.

  Dr. Lieberman threw himself into Running Man research with his usual creative zeal. Soon, students dropping by Lieberman’s office on the top floor of Harvard’s Peabody Museum were startled to find a sweat-drenched one-armed man with an empty cream-cheese cup strapped to his head running on a treadmill. “We humans are weird,” Lieberman said as he punched buttons on the control panel. “No other creature has been found with a neck like ours.” He paused to shout a question to the man on the treadmill. “How much faster can you go, Willie?”

  “Faster than this thing!” Willie called back, his steel left hand clanging against the treadmill rail. Willie Stewart lost his arm when he was eighteen after a steel cable he was carrying on a construction job got caught in a whirling turbine, but he recovered to become a champion triathlete and rugby player. In addition to the cream-cheese cup, which was being used to secure a gyroscope, Willie also had electrodes taped to his chest and legs. Dr. Lieberman had recruited him to test his theory that the human head, with its unique position directly on top of the neck, acts like the roof weights used to prevent skyscrapers from pitching in the wind. Our heads didn’t just expand because we got better at running, Lieberman believed; we got better at running because our heads were expanding, thereby providing more ballast.

  “Your head works with your arms to keep you from twisting and swaying in midstride,” Dr. Lieberman said. The arms, meanwhile, also work as a counterbalance to keep the head aligned. “That’s how bipeds solved the problem of how to stabilize a head with a movable neck. It’s yet another feature of human evolution that only makes sense in terms of running.”

  But the big mystery continued to be food. Judging by the Godzilla-like growth of our heads, Lieberman could pinpoint the exact moment when the caveman menu changed: it had to be two million years ago, when apelike Australopithecus—with his tiny brain, giant jaw, and billy-goat diet of tough, fibrous plants—evolved into Homo erectus, our slim, long-legged ancestor with the big head and small, tearing teeth perfectly suited for raw flesh and soft fruits. Only one thing could have sparked such a dramatic makeover: a diet no primate had ever eaten before, featuring a reliable supply of meat, with its high concentrations of calories, fat, and protein.

  “So where the fuck did they get it?” Lieberman asks, with all the gusto of a man who’s not squeamish about hacking into goats with a rock. “The bow and arrow is twenty thousand years old. The spearhead is two hundred thousand years old. But Homo erectus is around two million years old. That means that for most of our existence—-for nearly two million years!—hominids were getting meat with their bare hands.”

  Lieberman began playing the possibilities out in his mind. “Maybe we pirated carcasses killed by other predators?” he asked himself. “Scooting in and grabbing them while the lion was sleeping?”

  No; that would give us an appetite for meat but not dependable access. You’d have to get to a kill site before the vultures, who can strip an antelope in minutes and “chew bones like crackers,” as Lieberman likes to say. Even then, you might only tear off a few mouthfuls before the lion opened a baleful eye or a pack of hyenas drove you away.

  “Okay, maybe we didn’t have spears. But we could have jumped on a boar and throttled it. Or clubbed it to death.”

  Are you kidding? With all that thrashing and goring, you’d get your feet crushed, your testicles torn, your ribs broken. You’d win, but you’d pay for it; break an ankle in the prehistoric wilderness while hunting for dinner, and you might become dinner yourself.

  There’s no telling how long Lieberman would have remained stumped if his dog hadn’t finally given him the answer. One summer afternoon, Lieberman took Vashti, his mutty half border collie, for a five-mile jog around Fresh Pond. It was hot, and after a few miles, Vashti
plopped down under a tree and refused to move. Lieberman got impatient; yeah, it was a little warm, but not that bad….

  As he waited for his panting dog to cool off, Lieberman’s mind flashed back to his time doing fossil research in Africa. He recalled the shimmering waves across the sun-scorched savannah, the way the dry clay soaked up the heat and beamed it right back up through the soles of his boots. Ethnographers’ reports he’d read years ago began flooding his mind; they told of African hunters who used to chase antelope across the savannahs, and Tarahumara Indians who would race after a deer “until its hooves fell off.” Lieberman had always shrugged them off as tall tales, fables of a golden age of heroes who’d never really existed. But now, he started to wonder….

  So how long would it take to actually run an animal to death? he asked himself. Luckily, the Harvard bio labs have the best locomotive research in the world (as their willingness to insert a thermometer in a cheetah’s butt should make clear), so all the data Lieberman needed was right at his fingertips. When he got back to his office, he began punching in numbers. Let’s see, he began. A jogger in decent shape averages about three to four meters a second. A deer trots at almost the identical pace. But here’s the kicker: when a deer wants to accelerate to four meters a second, it has to break into a heavy-breathing gallop, while a human can go just as fast and still be in his jogging zone. A deer is way faster at a sprint, but we’re faster at a jog; so when Bambi is already edging into oxygen debt, we’re barely breathing hard.