The Marathon Gene

For years, it's been thought that humans made the ultimate evolutionary bargain. In exchange for the energy needed to develop our huge brains, we've had to sacrifice our physicality. We lack the strength, speed, and agility of our mammalian brethren, relying on our wits alone to survive. We are the naked, weak ape who provides for and protects his family by creating tools and outsmarting the rest of the animal kingdom.

As we're starting to learn, though, humans aren't just the smartest animals around: We're also the best endurance runners, and that's no small thing. Sure, being hairless means we're exposed to the elements, but it also means that we can move without overheating, and that our unique sweat glands can keep our body temperature regulated in even the hottest weather. Having more slow-twitch muscles means we're relatively pokey, but we can run longer distances than any other animals. And having smaller muscles means that, yes, we're puny, but also that there's less weight to carry around when we run.