Animal taxonomy is actually much weirder than you would think at first glance. The classic definition of species is the group of organisms which are capable of producing fertile offspring. However, there are also ring species, where you have populations A,B,C where B can interbreed with either A or C, but A cannot interbreed with C. Or in an alternate phrasing, members of B are members of both species A and species C. This obviously becomes intractable beyond a very few interbreeding populations.

So really, even nature favors composition over inheritance.