2007年VOA标准英语-Upright Walking by Human Ancestors May Have Beg

By Jessica Berman
Washington
31 May 2007

Scientists say early human ancestors may have begun walking on two legs on tree branches, not on the ground as commonly believed. The evidence contradicts the long-held belief that early humans first began walking upright on the ground. VOA's Jessica Berman reports.

The defining feature of human evolution is bipedalism which means walking on two legs.

Known as the Savannah hypothesis, paleontologists have long believed that bipedalism began after knuckle-walking primates¹, primates walking on all fours, descended² from trees to the ground.

While chimps³ and gorillas⁴ continue to use all fours to get around, human ancestors eventually learned to walk upright. It has been thought that bipedalism began at least 4.5 million years ago.

Now, two teams of British researchers are challenging the Savannah hypothesis.

Robin⁵ Crompton of the University of Liverpool in England says upright walking may have occurred between 17 and 24 million years ago, much earlier than anyone imagined.

"It goes back to whenever the date was for the common ancestor for all great apes," said Robin Crompton.

Crompton and colleagues at the University of Birmingham in England collected data for one year on tree-dwelling orangutans in the Sumatra rainforest in Indonesia.

Susannah Thorpe of Birmingham University describes what researchers call hand-assisted bipedalism, in which the orangutans moved their legs and used their arms primarily for balance on thin branches.

The primates were also observed straightening their legs on bending branches to keep from losing their balance, much the same way humans stiffen⁶ their legs while running on springy surfaces.

Thorpe says the observations are important, because they propose a less complicated theory of how humans came to walk upright.

"Our results remove the need for complicated scenarios⁷ like the Savannah that require human ancestors to move into a completely differently habitat," said Susannah Thorpe. "Instead straight-legged bipedalism simply relocates from the trees down to the ground."

The study on bipedalism is reported this week in the journal Science.

1 primates   

primate的复数

参考例句：

• Primates are alert, inquisitive animals. 灵长目动物是机灵、好奇的动物。
• Consciousness or cerebration has been said to have emerged in the evolution of higher primates. 据说意识或思考在较高级灵长类的进化中已出现。

2 descended   

a.为...后裔的，出身于...的

参考例句：

• A mood of melancholy descended on us. 一种悲伤的情绪袭上我们的心头。
• The path descended the hill in a series of zigzags. 小路呈连续的之字形顺着山坡蜿蜒而下。

3 chimps   

（非洲）黑猩猩( chimp的名词复数 )

参考例句：

• Chimps are too scarce, and too nearly human, to be routinely slaughtered for spare parts. 黑猩猩又太少，也太接近于人类，不可以作为人器官备用件说杀就杀。 来自英汉非文学 - 生命科学 - 医学的第四次革命
• And as nonprimates, they provoke fewer ethical and safety-related concerns than chimps or baboons. 而且作为非灵长类，就不会产生像用黑猩猩或狒狒那样的伦理和安全方面的顾虑。 来自英汉非文学 - 生命科学 - 医学的第四次革命

4 gorillas   

n.大猩猩( gorilla的名词复数 )；暴徒，打手

参考例句：

• the similitude between humans and gorillas 人类和大猩猩的相像
• Each family of gorillas is led by a great silverbacked patriarch. 每个大星星家族都由一个魁梧的、长着银色被毛的族长带领着。 来自《简明英汉词典》

5 robin   

n.知更鸟，红襟鸟

参考例句：

• The robin is the messenger of spring.知更鸟是报春的使者。
• We knew spring was coming as we had seen a robin.我们看见了一只知更鸟，知道春天要到了。

6 stiffen   

v.(使)硬，(使)变挺，(使)变僵硬

参考例句：

• The blood supply to the skin is reduced when muscles stiffen.当肌肉变得僵硬时，皮肤的供血量就减少了。
• I was breathing hard,and my legs were beginning to stiffen.这时我却气吁喘喘地开始感到脚有点僵硬。

7 scenarios   

n.[意]情节；剧本；事态；脚本

参考例句：

• Further, graphite cores may be safer than non-graphite cores under some accident scenarios. 再者，根据一些事故解说，石墨堆芯可比非石墨堆芯更安全一些。 来自英汉非文学 - 环境法 - 环境法
• Again, scenarios should make it clear which modes are acceptable to users in various contexts. 同样，我们可以运用场景剧本来搞清楚在不同情境下哪些模式可被用户接受。 来自About Face 3交互设计精髓