Humans, he said, have several adaptations that help us dump the enormous amounts of heat generated by running. These adaptations include our hairlessness, our ability to sweat, and the fact that we breathe through our mouths when we run, which not only allows us to take bigger breaths, but also helps dump heat.

“We can run in conditions that no other animal can run in,” Lieberman said.
While animals get rid of excess heat by panting, they can’t pant when they gallop, Lieberman said. That means that to run a prey animal into the ground, ancient humans didn’t have to run further than the animal could trot and didn’t have to run faster than the animal could gallop. All they had to do is to run faster, for longer periods of time, than the slowest speed at which the animal started to gallop.

All together, Lieberman said, these adaptations allowed us to relentlessly pursue game in the hottest part of the day when most animals rest. Lieberman said humans likely practiced persistence hunting, chasing a game animal during the heat of the day, making it run faster than it could maintain, tracking and flushing it if it tried to rest, and repeating the process until the animal literally overheated and collapsed.

Most animals would develop hyperthermia — heat stroke in humans — after about 10 to 15 kilometers, he said.