正如在生理特质上的进化学此消彼长一样，希尔斯说，在智力上也有此消彼长。

Just as there are evolutionary tradeoffs for physical traits, Hills says, there are tradeoffs for intelligence.

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他们推断，虽然一些进化上的变化涉及基因的丢失，因此是不可逆转的，但其他的变化可能是基因被关闭的结果。

They reasoned that while some evolutionary changes involve the loss of genes and are therefore irreversible, others may be the result of genes being switched off.

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Hence, selfish genes will lead to altruistic animals because, to the extent that evolution operates at the level of the genes, there's no hard and fast distinction between your own body and someone else's body.

所以，自私基因会导致利他行为，从这个意义上说,进化在基因层面进行，你自己的身体和别人的身体,没有严格差别。

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