Skip to navigation | Skip to content

Chimps in the gym teach us a thing or two

in the gym

Let's get physical ... chimps have been taught to walk on two legs and operate a treadmill in the name of science (Image: Cary Wolinsky)

Chimpanzees scampering on a treadmill have supported the notion that our ancient ancestors began walking on two legs because it used less energy than quadrupedal knuckle-walking, scientists say.

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

Chimpanzees are the closest genetic cousins to humans and are thought to have a common ancestor dating back 4-7 million years, depending on the estimate.

Some scientists for decades have advanced the hypothesis that millions of years ago, human ancestors began walking upright on two feet (bipedalism) 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," says one of the authors Assistant Professor David Raichlen, an anthropologist from the University of Arizona.

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

The chimpanzees were taught to walk quadrupedally and bipedally, the scientists say.

"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 says.

A walk on the wild side

Raichlen says chimpanzees sometimes walk on two legs in the wild, but are not very good at it.

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.

One, for example, used a longer stride and was more efficient walking on two legs than four, the researchers say.

They also looked at the fossil record of human ancestors and found anatomical features such as hind legs that might use less energy in locomotion, and pelvic structural changes allowing for more upright walking.

Humans not chimps show spite

In related research also published today in the Proceedings of the National Academy of Sciences, scientists show that chimps may take revenge but unlike humans don't do so out of spite.

Their study shows chimps would seek retribution when wronged but did not punish others out of spite, for instance if another chimpanzee was better off, says Keith Jensen, an evolutionary biologist at the Max Planck Institute for Evolutionary Anthropology in Germany, who led the study.

Tags: environment, palaeontology, zoology