Why Humans Walk on Two Legs

　　When our earliest ancestors started walking on two legs，they took the first steps toward becoming human, said lead researcher Michael Sockol of UC Davis1.Our findings help an,swer why. Sockol worked for two years to find an animal trainer willing to coax adult chimps to walk on two legs and to knucklewalk on all fours on the sort of treadmill found in most gyms.

　　Tile researchers found that human walking used about 75 percent less energy and burned 75 percent fewer calories than quadrupedal and bipedal2 walking in chimpanzees. They also found that for some but not all of the chimps，walking on two legs was no more costly than knucklewalking.

　　Taken together，the findings provide support for the hypothesis that anatomical differences affecting gait existed among our earliest apelike ancestors，and that these differences provided the genetic variation which natural selection could act on when changes in the environment gave bipeds an advantage over quadrupeds.

　　This isnt the complete answer, Soekol said.But its a good piece of a puzzle humans have always wondered about;How and why did we become human? And why do we alone walk on two legs?

　　chimpanzeen.黑猩猩 5baipedp

　　gaitn.步態，步法7AnE5tCmikp

　　quadrupedn.四足動物的5maiEsi:np

　　Calorien.卡 ,小卡5tredmIlp

　　coaxv.哄，哄勸

　　metabolicadj. 代謝的

　　注釋：

　　2. quadrupedal andbipedal：quad-：構詞詞素，是四的意思;bi-：構詞詞素，是二的意思; ped-：構詞詞素，是腳的意思;-al是構成形容詞的后綴，表示的。因此，quadrupedal 意為凹足動物的，bipedal意為二足動物的。

　　練習：

　　A Tile evidence why chimpanzees can be trained to use treadmills.

　　C The evidence why our apelike ancestors came to walk on two legs.

　　2. Which of the following best interprets the meaning of While the chimps

　　A While the chimps worked in the lab ...

　　C While the chimps tried to figure out what they should do ...

　　3. What was the result of the finding，according to Paragraph 5?

　　B One chimp used less energy walking on two legs.

　　D All of the above.

　　A Our apelike ancestors were anatomically different but had the same gaits.

　　C Our apelike ancestors could adapt to different climate changes due to genetic variation.

　　5. What does fossil and molecular evidence tell us about our earliest ancestors?

　　B Due to changes in climate，they were forced to travel between food patches.

　　D They could travel longer distances on the ground than those who could use less energy.

　　1. C 短文的第一段直接回答了這個問題。

　　3. D 第五段的第三、第四和第五句提供了答案。bipedalism was more expensive的意思是：兩足行走消耗更多的體能。walking upright的意思是：直立行走，即兩足行走。

　　5. C 倒數第二段提供了問題的答案。travel longer distances用的是比較級，這里是將兩足行走的猿人與上文中四足行走的猿人做比較。those who could cover more ground using less energy指的是上文提到的與四足行走的猿人相比，體能消耗較小的兩足行走猿人。其他選擇都不是正確說法。

　　Why Humans Walk on Two Legs

　　When our earliest ancestors started walking on two legs，they took the first steps toward becoming human, said lead researcher Michael Sockol of UC Davis1.Our findings help an,swer why. Sockol worked for two years to find an animal trainer willing to coax adult chimps to walk on two legs and to knucklewalk on all fours on the sort of treadmill found in most gyms.

　　Tile researchers found that human walking used about 75 percent less energy and burned 75 percent fewer calories than quadrupedal and bipedal2 walking in chimpanzees. They also found that for some but not all of the chimps，walking on two legs was no more costly than knucklewalking.

　　Taken together，the findings provide support for the hypothesis that anatomical differences affecting gait existed among our earliest apelike ancestors，and that these differences provided the genetic variation which natural selection could act on when changes in the environment gave bipeds an advantage over quadrupeds.

　　This isnt the complete answer, Soekol said.But its a good piece of a puzzle humans have always wondered about;How and why did we become human? And why do we alone walk on two legs?

　　chimpanzeen.黑猩猩 5baipedp

　　gaitn.步態，步法7AnE5tCmikp

　　quadrupedn.四足動物的5maiEsi:np

　　Calorien.卡 ,小卡5tredmIlp

　　coaxv.哄，哄勸

　　metabolicadj. 代謝的

　　注釋：

　　2. quadrupedal andbipedal：quad-：構詞詞素，是四的意思;bi-：構詞詞素，是二的意思; ped-：構詞詞素，是腳的意思;-al是構成形容詞的后綴，表示的。因此，quadrupedal 意為凹足動物的，bipedal意為二足動物的。

　　練習：

　　A Tile evidence why chimpanzees can be trained to use treadmills.

　　C The evidence why our apelike ancestors came to walk on two legs.

　　2. Which of the following best interprets the meaning of While the chimps

　　A While the chimps worked in the lab ...

　　C While the chimps tried to figure out what they should do ...

　　3. What was the result of the finding，according to Paragraph 5?

　　B One chimp used less energy walking on two legs.

　　D All of the above.

　　A Our apelike ancestors were anatomically different but had the same gaits.

　　C Our apelike ancestors could adapt to different climate changes due to genetic variation.

　　5. What does fossil and molecular evidence tell us about our earliest ancestors?

　　B Due to changes in climate，they were forced to travel between food patches.

　　D They could travel longer distances on the ground than those who could use less energy.

　　1. C 短文的第一段直接回答了這個問題。

　　3. D 第五段的第三、第四和第五句提供了答案。bipedalism was more expensive的意思是：兩足行走消耗更多的體能。walking upright的意思是：直立行走，即兩足行走。

　　5. C 倒數第二段提供了問題的答案。travel longer distances用的是比較級，這里是將兩足行走的猿人與上文中四足行走的猿人做比較。those who could cover more ground using less energy指的是上文提到的與四足行走的猿人相比，體能消耗較小的兩足行走猿人。其他選擇都不是正確說法。