[luckyme]

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Isn't the whole point of species to be able to classify creatures that are different into different groups? Obviously some groups of creatures are different from others so what is the problem?

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Dawkins point was that if all the past relatives of cats and dogs hadn't gone extinct there would be a slow morphing of one category into the other category and there wouldn't be any meaningful place to draw the lines.
"without gaps in the fossil record our whole system for naming species would break down."

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Your thought experiment sounds a lot like the joke about boiling a frog.

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It's Dawkins illustration and he does use a cold-to-hot example also.

luckyme