OK so a while ago I asked if it would be possible for a species that has been absorbed into another population by hybridization to later re-emerge from that population, and I was told that if two species can successfully hybridize and form fertile offspring, they're not really separate species. Is this correct?
I was wondering about this regarding the sharks, and also coyote-wolf hybrids, which are breeding successfully even though they seem to suffer a hit to fertility rates.