> Only same-species couples can reproduce This “definition” can so easily be reduced to the absurd by simply going back in time in steps to the common ancestor

> Only same-species couples can reproduce This “definition” can so easily be reduced to the absurd by simply going back in time in steps to the common ancestor of, say, humans and dogs, and then going up again, to then by transitivity prove that human beings and dogs are the same species, yet they cannot reproduce together. The classification of “species” is entirely arbitrary, any “definition” of it offered is shallow and pædantic.