Outrun This

A human won a Welsh town's annual Man versus Horse race for the first time in its 25-year history, BBC News reports. Huw Lobb finished the 22-mile course in 2 hours, 5 minutes and 19 seconds -- almost two minutes faster than the quickest equine. He takes home a 25,000-pound prize as well as bragging rights. Odds against a human victory were set at 16 to 1.

Excerpts below are from, Born To Run, By Ingfei Chen
DISCOVER Vol. 27 No. 05 May 2006 Biology & Medicine
http://www.discover.com/issues/may-06/features/tramps-like-us/?page=1
http://www.discover.com/issues/may-06/features/tramps-like-us/?page=2

Late one night over beers in the Welsh hamlet of Llanwrtyd Wells, an innkeeper got into an argument with a foxhunter about who could run faster, man or horse. The innkeeper insisted that over many miles, a human runner would have greater stamina, and prevail. Thus was born a tradition: Every year since 1980, Llanwrtyd Wells has hosted the Man Versus Horse Marathon, which pits hundreds of runners against dozens of horses with riders. On two legs or four, contestants take on 22 miles of challenging trails laced across a dazzling green countryside. They trot through fragrant pine forests, scramble up mountainous rock-strewn sheep trails, cross rolling moorlands, and ford rivers. In June 2004, for the first time ever, the human won. The innkeeper was delighted—and so were University of Utah biologist Dennis Bramble and Harvard University paleoanthropologist Daniel Lieberman. That summer the two scientists were putting the finishing touches on a theory with a new view on how conditions millions of years ago molded the way humans move today. The standard explanation among physical anthropologists has long been that early hominids left life in the trees to forage on the open savanna and that walking upright was the key to surviving in that new environment. Bramble and Lieberman do not dispute this general theory, but they have identified a suite of traits in the human anatomy that add a dramatic twist to the story line.

Unlike many mammals, not to mention primates, people are astonishingly successful endurance runners, "and I don't think it's just a fluke," Lieberman says. He and Bramble argue that not only can humans outlast horses, but over long distances and under the right conditions, they can also outrun just about any other animal on the planet—including dogs, wolves, hyenas, and antelope, the other great endurance runners. From our abundant sweat glands to our Achilles tendons, from our big knee joints to our muscular glutei maximi, human bodies are beautifully tuned running machines. "We're loaded top to bottom with all these features, many of which don't have any role in walking," Lieberman says.

A marathoner himself, David Carrier began to wonder about the role of endurance running in human evolution. People, he noted, can shed heat quickly—not by panting, like most animals, but by perspiring through millions of sweat glands. A lack of fur also helps dissipate heat more quickly. Carrier suspected that these traits were more relevant for handling physical exertion. The human body generates six times more heat when sprinting at top speed than when sitting in the sun. Most animals, humans included, must stop trotting when they overheat, or they die. (In one legendary experiment, Harvard biologists stuck a rectal thermometer into a cheetah, put the cat on a treadmill, and found that it refused to move once its temperature hit 105 degrees Fahrenheit, even though it was loping well below its top speed.) Given that humans excel at releasing heat and distance running, he speculated that we were built to run far and wide.

From the perspective of a vertebrate morphologist, humans lack one of the most obvious features of animals adapted for serious speed: a tail. In creatures that cover ground bipedally, such as kangaroos, kangaroo rats, and roadrunners, "the tail is the major balance organ," Bramble says. "In the whole history of vertebrates on Earth—the whole history—humans are the only striding biped that's a runner that's tailless." Still, Bramble eventually came to realize that people turn in remarkable performances. He once filmed a horse cantering, with Carrier running alongside at the same pace. The movie showed that Carrier's legs were churning more slowly than the horse's, which meant that the student's strides had to be spanning more distance per step than the horse's.

To glean insights into how bones grow—and thus to better interpret fossilized human jaws and skulls—the student wanted to see whether the repeated impact of running would spur a thickening of the pig's skull. "You know," Bramble said, "that pig's not holding its head still." He went on to explain that adept runners like horses, dogs, and rabbits keep their noggins remarkably steady as they lope, thanks to an obscure bit of anatomy called the nuchal ligament. It's a tendonlike band that links the head to the spine. People, he said, have a version of this band.

Rummaging through a collection of replicas of fossilized primate bones in a nearby lab, Bramble pointed out that the nuchal ligament leaves a trace—a delicate ridge—where it attaches at the base of the human skull. Then the scientists noticed the ridge in a pitted, yellowed skull of our 2-million-year-old relative Homo erectus—but not in older hominids known as australopithecines, who walked the earth as far back as 4.4 million years ago. "Holy moley!" Lieberman thought. "There's something going on here, and what's more, we might be able to study it in the fossil record."

"Your center of gravity, which is basically near your belt buckle, r-i-i-i-ses"—he takes a slow-motion step forward with his right leg and pauses, now up on the ball of his right foot—"so that it's over your leg." The body has now stored potential energy. The arch of the foot stiffens, and Lieberman pushes off against it. As he tips forward, potential energy converts to kinetic energy, and he swings his left foot ahead to complete the stride. But in running, he says, the legs become springs. You land on and squash the entire arch and bend your knee. So initially the body's center of gravity falls. "You go down—and then you go up," Lieberman says. Kinetic energy from the crash landing is stored in the many stretchy tendons of the arch and the leg, most notably the huge Achilles tendon connecting calf muscles to the heel bone. Like rubber bands, the tendons extend and then recoil—boing!—to launch you onto the next step.

"So why do we have all these tendons in our legs?" Lieberman asks. "You don't evolve big tendons unless you're a runner." Kangaroos, antelope, and other serious animal runners all have a great set of springs, which do nothing for walking. So our tendons can't be explained as being necessary for walking.

Without the balancing help of a tail, how do we avoid falling over when we run? The butt, it turns out, is crucial—right up there with the chin among traits that make us uniquely human. Chimps and other primates have little buns. Our own rear ends are huge; the upper part of the gluteus maximus is greatly expanded. Although few scholars have studied its role in running, the butt is, according to Bramble, "basically a substitute for a tail."

What that shows, says Lieberman, is that the butt isn't much involved during walking. In running, however, the body leans forward so that each time the leading foot strikes the ground, the trunk wants to topple forward. The gluteus maximus prevents that: It fires just before the foot slams into the floor, creating a braking action that keeps the torso from falling down.

Meanwhile, the way we pump our arms back and forth in a trot helps steady us too. And based on their experiments, the researchers suspect that the motions of our shoulders and arms actually help counterbalance the head, preventing it from pitching forward on each landing. Simultaneously, with each heel strike, certain shoulder muscles contract and put tension on the nuchal ligament, pulling up the skull and keeping it level. Our long neck is also important for running, Bramble says, because it allows the shoulders to twist freely of the head as we gaze forward.

About 2.6 million years ago, our forebears started eating meat and marrow, rich sources of protein and fat that perhaps eventually fueled the growth of larger brains. Bramble and Lieberman find it conceivable that endurance running helped hunters pursue prey to exhaustion.

Back in the 1980s, Carrier had read ethnographers' accounts of indigenous peoples who chased deer, antelope, and kangaroos to exhaustion under the scorching sun. The Tarahumara of the mountainous desert of northwestern Mexico, for example, were legendary runners. But by modern times, their running tradition had turned to sport: Men wearing simple tire-tread sandals bound with leather thongs compete in a 24-hour footrace that involves kicking a ball over about 100 miles of mountainous road. So Carrier, a triathlete in college, took it upon himself to prove his case. He and his younger brother, Scott, went to the desert in Utah and Wyoming to chase pronghorn antelope. The beasts ditched them every time. The sleek, bouncy animals would join up with others, and soon the men would be huffing after a dozen of them. "You wouldn't know which were the animals you started with," Carrier says.

For direct evidence of endurance hunting, Bramble and Lieberman point to the observations of Louis Liebenberg, author of The Art of Tracking: The Origin of Science, who has spent time on the traditional hunts of the Bushmen hunter-gatherers in the central Kalahari Desert in Botswana. Liebenberg ran with them when they chased down kudu antelope on two occasions. For eight other hunts he trailed them in his Land Cruiser, sometimes with a GPS device. The men attempted to run prey to exhaustion only when temperatures neared 100 degrees F, says Liebenberg. Three men would gulp a lot of water and head out together. Two initially did the hard work of tracking and pursuing over the arid grassland and woodland terrain, while the other held back. Eventually, the leaders dropped behind, leaving the third man to hound and spear the antelope when it reached its limit. "The animal will either just completely collapse, or it will actually slow down to a point where it just stands there . . . with sort of glazed-over eyes," Liebenberg says. "Essentially, you're pushing the animal to overheat." The hunters would then walk home with the meat, enough to share—in small portions—with the tribe.

During a chase, Liebenberg noted that the men maintained speeds of around 4 to 6 miles per hour, for anywhere from two to six and a half hours, and traversed up to 22 miles of terrain. These stats fall well within the performance range of the world's fastest competitive marathoners, who set a pace of roughly 12 miles an hour to cover 26 miles, albeit under far less harsh conditions.