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In the book, McDougall recounts the Harvard researcher’s eureka moment, which happened on a five-mile jog one summer afternoon with his half-mutt border collie, Vashti: It was hot, and after a few miles, Vashti plopped down under a tree and refused to move… As he waited for his panting dog to cool off, Lieberman’s mind flashed back to his time doing fossil research in Africa…Ethnographer’s reports he’d read years ago began flooding his mind; they told of African hunters who used to chase antelopes 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…but now he started to wonder. So how long would it take to actually run an animal to death?
Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen
By Christopher McDougall; Knopf; Out May 5 | Buy
Drawing on Harvard’s extant cache of locomotion data, Lieberman began crunching numbers comparing speed, body temperature, and body weight of humans and various conceivable prey. A deer and a decently fit man, Lieberman discovered, trot at almost an identical pace, but in order to accelerate, a deer goes anaerobic, while the man remains in an oxygenated jogging zone. The same is true for horses, antelopes, and a slew of other four-legged creatures. Since animals can run anaerobically only in short bursts before they must slow down to recover, a human in pursuit may have the final advantage. And because quadrupeds can’t pant while they run, they also quickly overheat. To run down dinner, Lieberman realized, might simply have been a matter of spurring the poor beast into a sprint enough times to make it collapse from hyperthermia.
“Running an animal to heatstroke is something that most humans can do, and that other animals can’t,” says Lieberman. “It’s a compelling explanation for why these capabilities evolved, and frankly, nobody’s come up with a better idea yet.”
But plenty of skeptics remain, some who doubt that persistence hunting was the reason humans evolved with the capacity for distance running, and some who doubt the ER hypothesis altogether. University of Wisconsin paleoanthropologist John Hawks, who researches the acceleration of human evolution since the advent of agriculture, questions how a trait that is supposedly specific to endurance running could persist today, when tools and farming have long since replaced the old selective pressures of hunting. “If these features really were distinctive to long-distance running, shouldn’t they have disappeared?” he asks.
Hawks also thinks that Lieberman and Rolian’s short-toe findings are essentially more evidence that humans are optimally designed for walking. “That’s exactly what we should expect,” Hawks says of the finding that toe-length variation does not affect walking. “If we see that toe length makes a big difference for running, that’s relatively good evidence that toe length wasn’t selected for.”
Still, ER theory has much on its side. Ultramarathoning is a cross-cultural phenomenon, and persistence hunting can be found in cultures all over the globe: The Kalahari Bushmen of Botswana, the Aborigines of Australia, the Masai of Kenya, and the Tarahumara are but a few examples of tribes whose lore includes the epic hunt. Hawks would argue this is a sophisticated cultural adaptation, but it could also mean that we have a common, fleet-footed ancestor.
Whether scientifically bona fide or not, it’s also hard to discount McDougall’s story of the Tarahumara’s supreme health and athleticism, and his sense of having tapped into something primordial — a feeling doubtlessly reinforced by his own metamorphosis from out-of-shape jogger to efficient ultradistance trekker. “They think it’s just a bunch of us crazy joggers out there who think running is important,” says Lieberman of his critics. The critics may be right about that, but it does seem that the endurance running hypothesis has legs.
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