[Doctor Stochastic]

Is your definition of a "kind" the transitive closure of matable individuals?

[DittoJed2]

Honestly, my definition of kind is less scientific sounding than that. What God meant to go together will go together and what He didn't won't. If it goes together and can reproduce, its a kind. If it goes together and suddenly stops producing even within the kind, it is still that original kind. It has mutated but it hasn't turned into a totally different "kind".