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Among all the primates, we humans are the only ones that stand on two legs.
在所有的靈長類動物中,人類是唯一能以兩條腿直立行走的。
You may have seen other animals stand on two legs briefly, such as a cat or a dog.
你可能看到過其他動物短暫的兩條腿站立,比如一只貓或一只狗。
But they always return to their original posture.
但是汪星人和喵星人總會回到原來的姿勢。
Even apes, who have arms and hands much like humans, still put them down to walk.
即使是擁有很像人類胳膊和手的猿類仍是用四肢走路。
How did it come about that we do every day what nobody else does?
人類的這種不同究竟是如何形成的?
Well, one theory says that standing up is the result of reaching up.
嗯,有一種理論表示直立是伸手的結果。
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.
你可能親眼見到過一只貓為了把食物從桌子上弄下來用后腿站立。
Suppose those same conditions remained in place for a hundred thousand generations.
假設那些相同條件仍然存在于成千上萬個世代。
The only food was always on tables, and only accessible to cats who could reach for it.
唯一的食物總是在桌子上,而只允許可以拿到它的貓享用。
In time, the cats who couldn't manage that trick would die out.
經過一段時間之后,不能深諳這一秘訣的貓們就會滅絕。
The ones who could manage it would survive and reproduce.
而拿到食物的喵星人生存下來并繁衍生息。
A cycle begins.
一個周期就這樣開始。
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.
據認為這樣的一種畫面可能使人類的祖先去從最先的四肢行走變成直立行走的生物。
In the forests and savannas where our species got its start, being able to reach up and pluck fruit trees was a good thing.
在森林和熱帶大草原,我們的祖先開始能夠摘取得樹上的果實無疑是一件好事。
We see chimpanzees do this even today, standing temporarily on two feet while grabbing food with their hands.
甚至今天我們也可以看到黑猩猩臨時性的雙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.
幾百萬年時間內,這些條件可能已經讓一種動物可以站起來,而不是短暫性。
That animal is us.
那種動物就是我們。
