Why can human beings outlast many faster four-legged animals when running long distances? Perhaps because early humans evolved as hunters on the hot African savannas. Humans developed the ability to release heat by sweating, but most mammals must pant, a function hard to regulate while running. Also, four-legged animals must adopt a pace that lets them breathe once in mid-stride; otherwise, the impact of the front legs hitting the ground will prevent deep inhalation. Humans can vary the number of breaths per stride, set a pace unsuited to the prey, and so eventually exhaust it.