第四部分 补全短文

Researchers Discover Why Humans Began Walking Upright

Most of us walk and carry items in our hands every day. These are seeminglysimple activities that the majority of us don’t question. But an internationalteam of researchers, including Dr. Richmond from GW's Columbian College of Artsand Sciences，have discovered that human walking upright, may have originatedmillions of years ago as an adaptation to carrying scarce, high- qualityresources. The team of researchers from the U. S., England, Japan and Portugalinvestigated the behavior of modern-day chimpanzees as they competed for foodresources，in an effort to understand what ecological settings would lead a largeape — one that resembles the 6 million-year old ancestor we shared in commonwith living chimpanzees — to walk on two legs.

“These chimpanzees provide a model of the ecological conditions under whichour earliest ancestors might have begun walking on two legs, "，said Dr.Richmond.

The research findings suggest that chimpanzees switch to moving on two limbsinstead of four in situations where they need to monopolize a resource. Standingon two legs allows them to carry much more at one time because it frees up theirhands. Over time，intense bursts of bipedal activity may have led to anatomicalchanges that in turn became the subject of natural selection where competitionfor food or other resources was strong.

Two studies were conducted by the team in Guinea. The first study wasconducted by the team in Kyoto University’s “ outdoor laboratory ” in a naturalclearing in Bossou Forest. Researchers allowed the wild chimpanzees access todifferent combinations of two different types of nut — the oil palm nut，which isnaturally widely available, and the coula nut, which is not. The chimpanzees’behavior was monitored in three situations:(a) when only oil palm nuts wereavailable,(b)when a small number of coula nuts were available，and(c) when coulanuts were the majority available resource.

When the rare coula nuts were available only in small numbers, thechimpanzees transported more at one time. Similarly, when coula nuts were themajority resource, the chimpanzees ignored the oil palm nuts altogether. Thechimpanzees regarded the coula nuts as a more highly-prized resource andcompeted for them more intensely.

In such high-competition settings，the frequency of cases in which thechimpanzees started moving on two legs increased by a factor of four. Not onlywas it obvious that bipedal movement allowed them to carry more of this preciousresource, but also that they were actively trying to move as much as they couldin one go by using everything available 一 even their mouths.

The second study, by Kimberley Hockings of Oxford Brookes University, was a14-month study of Bossou chimpanzees crop-raiding, a situation in which theyhave to compete for rare and unpredictable Resources. Here, 35 percent of thechimpanzees activity involved some sort of bipedal movement, and once again,this behavior appeared to be linked to a clear attempt to carry as much aspossible at one time.

参考答案： BAEFC