Humans walk upright to save energy

: 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.

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.

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.

“This paper provides strong support for the fact that energy savings played a role in the evolution of bipedalism,” one of the scientists, University of Arizona anthropologist David Raichlen, said in a telephone interview. The chimpanzees were taught to walk on the treadmill both quadrupedally and bipedally, the scientists said.

“These guys are smart enough that they would hit the stop button on the treadmill when they were done. If they didn’t want to walk on the treadmill, they’d just hit the stop button or they’d jump off,” Raichlen said.

Overall, the chimpanzees used about the same amount of energy walking on two legs compared to four legs, but the researchers saw differences among the individual animals in how much energy they used based on their gaits and anatomy.

Source: The Times Of India

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