Elite human runners, however, can sustain speeds up to 6.5 meters per second. Even run-of-the-mill joggers typically do between 3.2 and 4.2 meters per second, which means they can outrun dogs at distances greater than two kilometers.
Our "sustainable distance" is also hard to beat. African hunting dogs typically travel an average of 10 kilometers a day. Wolves and hyenas tend to go about 14 and 19 kilometers, respectively. In repeated distance runs, horses can cover about 20 kilometers a day. Vast throngs of human runners, by comparison, routinely run 42.2-kilometer marathons in just a few hours, and each year tens of thousands of people complete ultra-marathons of 100 kilometers and longer. (A few animals can match that under special circumstances. Huskies can trot up to 100 kilometers in Arctic conditions when forced to by people. But in warmer climes—no way.)
Given all this, you might wonder why it took so long for a human to win the Man vs. Horse Marathon. For one thing, the world’s top runners rarely compete in oddball races in rural Wales. And the 22-mile run (the Welsh race is shorter than the standard 26.2-mile marathon) through a damp, shady landscape doesn't usually heat-stress horses much, thus largely negating the human runners’ edge. (Not surprisingly, the weather has been notably warm when men prevailed.) Human runners, by the way, have also sometimes won the annual Man Against Horse Race in Prescott, Ariz., in which contestants clamber up and down a mountain on 50 miles of rocky trails.
But how did we get this way? After all, our brainy, tool-using ancestors could have just sneaked up on prey animals and brought them down with a spear or arrow. Why did evolution shape us as great distance runners?
The answer, argue Lieberman and Bramble, is that snares, nets, and really effective projectile weapons, such as the bow and arrow, were probably invented by Homo sapiens—modern humans. There's no evidence that early Stone Age hunters had weapons much better than sharp sticks. Such armaments would have required them to kill prey animals at close quarters, where they would have been at high risk of getting fatally gored, bitten, or kicked. Thus, they probably obtained meat mainly via "persistence hunting"—chasing an antelope, for instance, until it was nearly keeling over with heat exhaustion—and scavenging. The latter was very much a running game: When distant, circling vultures tipped them off about a lion kill, they had to get there before hyenas, which strip everything edible from carcasses. And they typically could only outrace hyenas in the hot sun. As a result, they carved out a new carnivore niche: the hot-day meat chaser.
Intriguingly, existing hunter-gatherers still sometimes resort to persistence hunting in hot weather. That's because the nutritional payoffs can greatly exceed the energy costs of running down meat for us fleet-footed types. In fact, our ancestors' meat-rich diets probably contributed to the evolution of modern human traits, such as small guts, small teeth, and big brains.
Elaborating on this idea, Mark Mattson, a neuroscientist at the National Institute on Aging, has proposed that our kind evolved superior smarts partly because they helped us record and recall the complex details we encountered when running after food—landmarks, tracking clues, location of water sources, and so on. The fact that endurance exercise is known to stimulate neuronal growth in the brain’s memory-forming hippocampus suggests he's right. A related recent study also suggests that natural selection endowed us with the ability to experience the “runner's high,” wiring the brain so that endurance exercise lights up its "endocannabinoid" system in a pleasurable way to reinforce a tendency toward high-intensity running.
In sum, you might say we were born to run. But you also might just as well say we ran to be born. Come to think of it, that would make a seriously good motto for the Wales marathon.