Why Humans Walk On Two Legs A team of scientists that studied chimpanzees trained to use treadmills has gathered new evidence suggesting that our earliest apelike ancestors started walking on two legs because it required less energy than getting around on all fours. The five chimps also wore face masks used to help the researchers measure oxygen consumption. While the chimps worked out, the scientists collected metabolic and other data that allowed them to calculate which method of locomotion used less energy and why. The team gathered the same information for four adult humans walking on a treadmill. We were prepared to find that all of the chimps used more energy walking on two legs but that finding wouldnt have been as interesting, Sockol said. What we found was much more telling. For three chimps, bipedalism3 was more expensive, but for the other two chimps, this wasnt the case. One spent about the same energy walking on two legs as on four. The other used less energy walking upright. These two chimps had different gaits and anatomy than their knucklewalking peers. Fossil and molecular evidence suggests the earliest ancestors of the human family lived in forested areas in equatorial Africa in the late Miocene era some 8 to 10 million years ago, when changes in climate may have increased in distance between food patches. That would have forced our earliest ancestors to travel longer distances on the ground and favored those who could cover more ground using less energy. 词汇： chimp )calorie n. 卡，小卡 treadmill n. 踏轮;踏车;单调工作gait n. 步态，步法 knucklewalk v. 用膝关节走路Quadruped n. 四足动物 locomotion n. 运动 1. UC Davis ：加州大学戴维斯分校。UC是University of California 的缩写，该校有多个分校，UC Davis是其中一个。Davis以前是UC Berkeley分校的农学院，后来独立出来。Davis是一个大学城，很小的城市，Davis校园基本就构成了这个城市。 3. bipedalism：系bipedal的对应名词，这里后缀-ism表示特征、特性。 1. What did Michael Sockol and his team find out in their study of chimpanzees? B) The evidence why our apelike ancestors came to walk on four legs. D) The evidence why chimpanzees can be trained to walk on two legs. A) While the chimps worked in the lab. C) While the chimps tried to figure out what they should do.-