Homo sapiens are nowhere near the fastest runners in the animal kingdom. But what we lack in speed, we make up for in endurance. And we're specially equipped to go the distance. We've got bigger butt muscles than other primates. We lost most of our fur, too, and sprouted lots of sweat glands, to help us cool off.
Scientists believe our endurance running abilities began to appear two million to three million years ago, around the time the genus homo came about. And a new study suggests that a mutation in one key gene had something to do with it.