Chimps on treadmill offer human evolution insight

By Will Dunham

WASHINGTON (Reuters) - Chimpanzees scampering on a treadmill have provided support for the notion that ancient human ancestors began walking on two legs because it used less energy than quadrupedal knuckle-walking, scientists said.

Writing on Monday in the Proceedings of the National Academy of Sciences, the researchers said people walking on a treadmill used just a quarter of the energy relative to their size compared to chimpanzees knuckle-walking on four legs.

The scientists equipped five chimpanzees and four people with face masks to track oxygen usage and looked at other measures to assess energy expenditure and biomechanics on a treadmill.

Bipedalism is a defining characteristic of the human lineage and marked an important divergence from other apes.

Chimpanzees are the closest genetic cousins to people. They are thought to have a common ancestor with humans dating back anywhere between 4 million and 7 million years, depending

on the estimate.

Some scientists for decades have advanced the hypothesis that millions of years ago, human ancestors began walking upright because it used less energy than quadrupedal walking, gaining advantages in things like food foraging.

But there has been scant data on this notion, aside from a 1973 study looking at locomotion energy in juvenile chimps.