Were humans evolved to be runners?

The New York Times offers an interesting speculation on the evolution of the human body.

The scientific evidence supports the notion that humans evolved to be runners. In a 2007 paper in the journal Sports Medicine, Daniel E. Lieberman, a Harvard evolutionary biologist, and Dennis M. Bramble, a biologist at the University of Utah, wrote that several characteristics unique to humans suggested endurance running played an important role in our evolution.

Most mammals can sprint faster than humans — having four legs gives them the advantage. But when it comes to long distances, humans can outrun almost any animal. Because we cool by sweating rather than panting, we can stay cool at speeds and distances that would overheat other animals. On a hot day, the two scientists wrote, a human could even outrun a horse in a 26.2-mile marathon.

Why would evolution favor the distance runner? The prevailing theory is that endurance running allowed primitive humans to incorporate meat into their diet. They may have watched the sky for scavenging birds and then run long distances to reach a fresh kill and steal the meat from whatever animal was there first.

Other research suggests that before the development of slingshots or bows, early hunters engaged in persistence hunting, chasing an animal for hours until it overheated, making it easy to kill at close range. A 2006 report in the journal Current Anthropology documents persistence hunting among modern hunter-gatherers, including the Bushmen in Africa.

“Ancient humans exploited the fact that humans are good runners in the heat,” Dr. Bramble said. “We have such a great cooling system” — many sweat glands, little body hair.

There is other evidence that evolution favored endurance running. A study in The Journal of Experimental Biology last February showed that the short toes of the human foot allowed for more efficient running, compared with longer-toed animals. Increasing toe length as little as 20 percent doubles the mechanical work of the foot. Even the fact that the big toe is straight, rather than to the side, suggests that our feet evolved for running.

“The big toe is lined up with the rest, not divergent, the way you see with apes and our closest nonrunning relatives,” Dr. Bramble said. “It’s the main push-off in running: the last thing to leave the ground is that big toe.”

Springlike ligaments and tendons in the feet and legs are crucial for running. (Our close relatives the chimpanzee and the ape don’t have them.) A narrow waist and a midsection that can turn allow us to swing our arms and prevent us from zigzagging on the trail. Humans also have a far more developed sense of balance, an advantage that keeps the head stable as we run. And most humans can store about 20 miles’ worth of glycogen in their muscles.

And the gluteus maximus, the largest muscle in the human body, is primarily engaged only during running. “Your butt is a running muscle; you barely use it when you walk,” Dr. Lieberman said. “There are so many features in our bodies from our heads to our toes that make us good at running.”

This makes a good case, and it is well-known in medical circles that a human in training can run down a horse given several days. The horse can always sprint away at first, but the human continues to run and catches up when the horse stops to rest. After a day or so, the horse will simply stop running away and the human catches it. The human, if trained, is capable of greater long term endurance than the horse does.

Interesting, no?