[AndrewC]

Since the coelocanth has come into discussion again, I thought I would note that there's no evidence that the coelocanths of today could reproduce with the coelocanth of 100 million years ago.

What is your point? Is it that if two things can produce viable offspring they are the same species?

[AntiGuv]

No. There are those aberrations (i.e. horse & donkey) where different species can produce viable offspring. My point, however, is that when two populations can never produce viable offspring via natural means, then they are invariably of different species. This means that if a coelocanth of today has drifted far enough away from a coelocanth of 100 million years ago that they would be unable to mate, then the two are genotyped as different species even if their phenotypes are virtually identical.