Laziness Could be the Basis of Bipedalism, Human Civilization

Why do humans walk on two legs? Because it's easier than walking on four.

That's the answer of University of Arizona anthropologist David Raichlen to the perplexing question of bipedalism.

Walking on two legs is part of what makes humans so special. Keep our ancestors on all fours, and their hands never get free enough to use those conveniently opposable thumbs, thereby setting in motion a positive feedback loop between tool, culture and development.

But why did they stand up and stay that way? Did they have dim primate inklings that their free hands would someday erect a civilization capable of producing round-the-clock Paris Hilton coverage and sugar-free ice cream? To answer these questions, Raichlen put some chimps on a treadmill and hooked them up to oxygen masks.

The chimps were measured both while walking upright and while moving on their legs and knuckles. That measurement of the energy needed to move around was compared with similar tests on humans and the results are published in this week's online edition of Proceedings of the National
Academy of Sciences.

It turns out that humans walking on two legs use only one-quarter of the energy that chimpanzees use while knuckle-walking on four limbs.
And the chimps, on average, use as much energy using two legs as they did when they used all four limbs.

But unpack that average, and it turns out that one chimp used less energy than the others when walking on two legs. Send him back a few million years, and in time that chimp's descendants might have become
... us.

Humans walk upright to conserve energy [Associated Press]

Chimpanzee locomotor energetics and the origin of human bipedalism [Proceedings of the National Academy of Science]