Did domestic canine Pokemon descend from wilder Pokemon like Mightyena, or is there no real evolutionary history for the overall canine family? (I do hope this makes science. Biology and it’s vocabulary was not my strong suit in school.)

They did indeed! In fact, mightyena are themselves descendants from the same common ancestor as growlithe, lillipup, and so forth.

I could go further into detail as to when, roughly, each species diverged, but this may overcomplicate matters a bit. The important thing to know is that, indeed, mightyena is very closely related to the “dog” pokémon—possibly, even, to the point where a proto-mightyena might have been the common ancestor and that human domestication led to dog-like pokémon adapting into their own species.

It’s actually quite interesting to look at, actually. Each of the dog-like species share similar traits, but it’s very easy to tell why they were domesticated based on what types they’ve become. But that’s neither here nor there, I suppose.