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.
Ah, yes, the gluteus maximus, primarily engaged only during jogging, punching, lifting, tackling, sprinting, throwing, and swinging a club.
And most humans can store about 20 miles’ worth of glycogen in their muscles.... “Ancient humans exploited the fact that humans are good runners in the heat,” Dr. Bramble said. “We have such a great cooling system”
Which allows us to perform any endurance activity over long distances, including swimming. Or carrying a kill back to camp. Or carrying water, children, tools, and materials for building shelter. Pretty much any hard work.
Haven't any of these scientists noticed that it's easy to get tired and overheat while building a fence in your back yard? For many animals, running might be the only thing they do that causes them to overheat, but when you're an intelligent, tool-using, shelter-building, material-possessions-lugging human, there are lots of things that can tire you out or give you heatstroke on a warm day.
If I remember correctly, the hunter-gatherers in the Jared Diamond television special based on Guns, Germs, and Steel didn't spend much time jogging. They walked, climbed, and paddled. They chopped down trees and carried heavy stuff. They hunted in the forest, stalking and then sprinting to attack. Their efficient cooling system, powerful glutes, and springy tendons served them admirably in all of these activities. Obviously they had a very different culture from the San Bushmen in Africa -- how can we be sure what culture and environment had the greatest influence on our physical evolution? I have read that the San seem to be closer to our origins, geographically, linguistically, and genetically, but it is all speculative. Even if they are our closest contemporary link to our evolutionary origins, we can't assume their lifestyle resembles the lifestyle of our ancestors.
Furthermore, a lot of the popular appeal behind the "born to run" idea is based on simple astonishment at the difference between trained and untrained people. Running is the example that has caught the popular imagination, but many other physical activities could lead to the same result. For example, with regular training, ordinary people can learn to lift way more than you would expect, enough to convince a man on the street that people are "built to lift heavy stuff." If you found a tribe that was as into lifting stuff as the Tarahumara are into running, I'm sure you would find examples of older people lifting burdens that would amaze us. And then it would seem quite obvious that our powerful glutes and efficient cooling system were evolved to help us carry game back to camp, swing heavy primitive axes and weapons, lift baskets of wild yams, and carry animal skins filled with water.