The difficulty delineating species has been considered evidence for evolution since long before Darwin. The concept of species is man made. There is nothing in biology that requires drawing strict lines between populations.
Um, yes, there is otherwise they wouldn't have tried in the first place. It is evolutionists that are not bothered with precision - not biologists. Biologists, are rather bothered with precision. Thus the schizophrenia that ocurrs when you mix the two. Shall I call for nurse Ratchet for you?