Among all the primates, we humans are the only ones that stand on two legs.
在所有的灵长类动物中,人类是唯一能以两条腿直立行走的。
You may have seen other animals stand on two legs briefly, such as a cat or a dog.
你可能看到过其他动物短暂的两条腿站立,比如一只猫或一只狗。
But they always return to their original posture.
但是汪星人和喵星人总会回到原来的姿势。
Even apes, who have arms and hands much like humans, still put them down to walk.
即使是拥有很像人类胳膊和手的猿类仍是用四肢走路。
How did it come about that we do every day what nobody else does?
人类的这种不同究竟是如何形成的?
Well, one theory says that standing up is the result of reaching up.
嗯,有一种理论表示直立是伸手的结果。
Think of it this way.
想象一下。
You may have seen a cat go up on its hind legs in order to pull food down off a table.
你可能亲眼见到过一只猫为了把食物从桌子上弄下来用后腿站立。
Suppose those same conditions remained in place for a hundred thousand generations.
假设那些相同条件仍然存在于成千上万个世代。
The only food was always on tables, and only accessible to cats who could reach for it.
唯一的食物总是在桌子上,而只允许可以拿到它的猫享用。
In time, the cats who couldn't manage that trick would die out.
经过一段时间之后,不能深谙这一秘诀的猫们就会灭绝。
The ones who could manage it would survive and reproduce.
而拿到食物的喵星人生存下来并繁衍生息。
A cycle begins.
一个周期就这样开始。
It is thought that this kind of scenario may have led the predecessors to human beings to go from being four-footed to being upright creatures.
据认为这样的一种画面可能使人类的祖先去从最先的四肢行走变成直立行走的生物。
In the forests and savannas where our species got its start, being able to reach up and pluck fruit trees was a good thing.
在森林和热带大草原,我们的祖先开始能够摘取得树上的果实无疑是一件好事。
We see chimpanzees do this even today, standing temporarily on two feet while grabbing food with their hands.
甚至今天我们也可以看到黑猩猩临时性的双腿站立用手抓取食物。
Given a few million years, these conditions may have given rise to an animal that can stand up all the time, not just briefly.
几百万年时间内,这些条件可能已经让一种动物可以站起来,而不是短暂性。
That animal is us.
那种动物就是我们。
