1 . Why did humans evolve to walk upright? Perhaps because it’s just plain easier. Make that “energetically less costly,” in science-speak.
Bipedalism — walking on two feet — is one of the defining characteristics of being human, and scientists have debated for years how it came about. In the latest attempt to find an explanation, researchers trained five chimpanzees to walk on treadmill while wearing masks that allowed measurement of their oxygen consumption. The chimps were measured both while walking upright and while moving on their legs and knuckles. That measurement of the energy needed to move round was compared with similar tests on humans and the results are published in this week’s online edition of Proceedings of the National Academy of Sciences.
It turns out that humans walking on two legs use only one quarter of the energy that chimpanzees use while knuckle-walking on four limbs. And the chimps, on average, use as much energy using two legs as they did when they used all four limbs.
However, there were differences among chimpanzees in how much energy they used, and this difference corresponded to their different gaits and anatomy. One of the chimps used less energy on two legs, one used about the same and the others used more, said David Raichlen, assistant professor of anthropology at the University of Arizona.
“What we were surprised at was the variation,” he said in 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.”
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.”
The research was supported by the National Science Foundation and the L. S. B. Leakey Foundation.
1. The underlined word “Bipedalism” means .| A．moving sideways | B．walking upright |
| C．walking on four legs | D．running fast |
| A．Masks protect chimpanzees from any harm. |
| B．Masks help chimpanzees walk steadily. |
| C．There was heavy smoke in the room. |
| D．Masks helped to measure how much oxygen chimpanzees consumed. |
| A．have no idea on how human walking on two legs came about |
| B．have had different views on why chimpanzees walk on four legs |
| C．have had different views on how human walking on two legs came about |
| D．have had similar views on how human walking on two legs came about |
| A．How did chimpanzees save energy? | B．Why didn’t chimpanzees walk on two legs? |
| C．David Raichlen researched into chimpanzees. | D．Different chimpanzees consume different energy. |
| A．conserve energy | B．differ from other animals |
| C．free their brains | D．strengthen their legs |
