Born to run?

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.