Reciprocal altruistic behavior exists not only among organisms but also in the society, but it has been hard to explain the altruistic behavior of organisms to the classical natural selection theory.

互惠利他行为是生物有机体乃至人类社会普遍存在的一种现象，经典的自然选择学说难以解释生物有机体的这类行为。

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An early visitor was Charles Darwin nearly 175 years ago, on a trip that inspired his theory of evolution by natural selection.

大约在175年前，一位早期的访客在旅途中得到灵感-自然选择学说产生了，他就是查尔斯·达尔文。

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Darwin's theory of natural selection is intended to answer this question.

达尔文的自然选择理论正是为了回答这个问题。

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And she explains the theory of evolution through natural selection in a way that both children and adults will enjoy.

VOA: special.2009.02.27

And it might occur to some of you that this seems to be an analogy with the Darwinian theory of natural selection where there's a random assortment of random mutations.

也许你们之中会有人觉得,这和达尔文的自然选择理论,看上去很相似,自然选择就是随机突变的随机分配。

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He developed the theory of evolution that life on Earth developed through the process of natural selection.

VOA: special.2009.12.16

Charles Darwin, by contrast, found a lead for his theory of natural selection in the whimsical hobby of pigeon fancying, where the birds showed an enormous variety of form and behaviour.

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The theory of evolution by natural selection states the "fittest" animals or plants are more likely to survive and reproduce.

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Wallace, who was born in Monmouthshire and also lived in Neath, was the co-discoverer of the theory of evolution by natural selection.

BBC: Alfred Russel Wallace's 19th Century letters go online