Randolph E. Schmid, Associated Press
"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.
Walking on two legs freed our arms, opening the door to manipulating the world, Raichlen said. "We think about the evolution of bipedalism as one of first events that led hominids down the path to being human."
Theirs is the latest of several explanations for walking upright. Among the others have been the need to used the arms in food gathering, the need to use the upper limbs to bring food to a mate and offspring and raising the body higher to dissipate heat in the breeze.
The research was supported by the National Science Foundation and the L. S. B. Leakey Foundation.
