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Humans started walking upright to save energy

Standing UprightWhy did humans evolve to walk upright? Perhaps because it is just plain easier. Make that "energetically less costly," in science-speak, and you have the conclusion of researchers who are proposing a likely reason for our modern gait.

In the latest attempt to find an explanation, researchers trained five chimpanzees to walk on a treadmill while wearing masks that allowed measurement of their oxygen consumption. The chimps were measured both while walking upright and while moving on their legs and knuckles.

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.

However, there was variability among chimpanzees in how much energy they used, and this difference corresponded to their different gaits and anatomy.

One of the chimps used less energy on two legs, one used about the same and the others used more, said David Raichlen, assistant professor of anthropology at the University of Arizona.

"What we were surprised at was the variation," he said in a telephone interview. "That was pretty exciting, because when you talk about how evolution works, variation is the bottom line, without variation there is no evolution."

If an individual can save energy moving around and hunting and spend more of it on reproduction, "that's how you end up getting new species," he said.

Link & Image: USA Today
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