为什么鸟类都是前肢进化成翅膀,而不是再进化出一双翅膀而保留四肢?这样不是方便的多吗? 知乎 Template




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tomski为什么鸟类都是前肢进化成翅膀,而不是再进化出一双翅膀而保留四肢?这样不是方便的多吗? 知乎 coloring