【英语时差8，16】直立行走-2

 Last time we discussed how human beings are the only primate¹ that walks on two feet.   One theory for how this might have happened says that, when our species was just getting its start, reaching up for fruit was a good thing to be able to do. Those who could temporarily rear up on two feet could get more food, and thus had a survival advantage over those who couldn't. In time, those who could stand on two feet indefinitely beat out those who could only do it temporarily. In time you have the modern, free-standing² human form.

But you may have noticed that human beings are good at doing a lot of other things than just picking fruit. These days we can stroll around on two feet at will. Our hands are free to do all sorts of things, from building space stations to building radio stations. Our brains have grown much larger than they were when we lived in trees. We have become a radically³ different kind of creature.

If you can get a sense of how this has happened, you will have understood something wonderful about evolution. First comes the competition over fruit. The animal that stands the best survives and reproduces, passing on its characteristics. But now you have a lot of standing animals. A standing animal can see predators⁴ from farther away, another survival advantage. Standing also means your forelimbs can be used to manipulate objects and create tools. One thing leads to another and another and another. Across millions of years, a little thing like grabbing fruit can trigger an entire change of species.

1 primate   

n.灵长类（目）动物，首席主教；adj.首要的

参考例句：

• 14 percent of primate species are highly endangered.14%的灵长类物种处于高度濒危状态。
• The woolly spider monkey is the largest primate in the Americas.绒毛蛛猴是美洲最大的灵长类动物。

2 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

3 radically   

ad.根本地，本质地

参考例句：

• I think we may have to rethink our policies fairly radically. 我认为我们可能要对我们的政策进行根本的反思。
• The health service must be radically reformed. 公共医疗卫生服务必须进行彻底改革。

4 predators   

n.食肉动物( predator的名词复数 )；奴役他人者（尤指在财务或性关系方面）

参考例句：

• birds and their earthbound predators 鸟和地面上捕食它们的动物
• The eyes of predators are highly sensitive to the slightest movement. 捕食性动物的眼睛能感觉到最细小的动静。 来自《简明英汉词典》