A chimpanzee walks on a treadmill in this undated handout. 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 July 16, 2007. 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. (Xinhua/Reuters Photo)
WASHINGTON, July 16 (Xinhua) -- Walking on two legs
costs humans only one-quarter the energy expended by chimpanzees who
knuckle-walk on four legs, according to a new research conducted by U.S.
This saving in energy may have been what originally
drove our common ancestor to walk upright, anthropologists from University of
Arizona and Washington University, St. Louis reported Monday on the latest issue
of Proceedings of the National Academy of Sciences.
The research team measured how much oxygen five
chimpanzees and four human volunteers burned as they walked on a treadmill: the
chimps on four legs or two legs, the humans just on two.
For a given weight, the humans were far more efficient than chimps on two legs. The chimps, on average, used as much oxygen on two legs as on four. However, one chimp, with a longer stride, was more efficient walking upright.
Walking on two legs costs humans only one-quarter the energy expended by chimpanzees who knuckle-walk on four legs. (File Photo)
According to biomechanical equations, energy
consumption increases either with shorter steps or more active muscle mass. Long
legs and a change in pelvic structure enable humans to reduce both factors,
according to anthropologists.
The fact that variation exists even among a small
population of chimps, the authors say, makes it reasonable to assume that human
ancestors may have been selected for their efficiency in walking.