By the interbreeding criterion every individual is a member of the same species as its parents. This is an unsurprising, not to say platitudinously obvious conclusion, until you realise that it raises an intolerable paradox in the essentialist mind. Most of our ancestors throughout evolutionary history have belonged to different species from us by any criterion, and we certainly couldn’t have interbred with them. In the Devonian Period our direct ancestors were fish. Yet, although we couldn’t interbreed with them, we are linked by an unbroken chain of ancestral generations, every one of which
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