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Message: <blockquote data-quote="Mysticete" data-source="post: 3497300" data-attributes="member: 67784">But how many hybrids are needed to "verify" BSC is in place? Even the most staunch BSC advocates in Ornithology don't believe the existence of hybrids is sufficient to lump a species. You need to prove free interbreeding with hybrid offspring being fully fertile and and not having negative selective pressure against them. That's easier said than done. Plenty of species hybridize when in contact....however if those hybrid zones are narrow and not expanding, it's generally not considered a problem for keeping the two species in isolationAnd that doesn't even get into the problem of allopatry. If the two species geographically never come into contact, your left again to arbitrarily determine "how different" the populations are, and whether that difference is sufficient for splitting and lumping.</blockquote>