Why did humans evolve to walk upright?

人类为何进化到了直立行走的姿态？

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Like several of the newly described species, the DogCroc was able to walk upright.

向许多新发现的物种一样，犬鳄可以直立行走。

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We walk upright on two legs and our newborns are helpless. Our babies are unusually large.

我们用两条腿直立行走，我们的新生宝宝非常无助，也大得不寻常。

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New fossil evidence seems to confirm that a key ancestor of ours could walk upright consistently - one of the major advances in human evolution.

BBC: Fossil find puts 'Lucy' story on firm footing

There is some evidence that much older hominids could walk upright.

BBC: NEWS | Science/Nature | Scientists unearth early skeleton

The simplest theory is that these swellings dwindled to nothing after our ancestors began to walk upright, because the costs of advertising ovulation in this way came to outweigh any benefits.

NEWYORKER: It Ain��t Necessarily So