Not impossible... just that the results would not have been contributing to the gene pool of either species.
I'm not saying on some cold lonely night, things didn't happen. Mules happen in the wild too you know.
wa:do
I don't know about mules mate, I've seen more than a few people who appear to be carrying certain genetic characteristics of the ancient Neanderthals walking our streets today, with their protuding foreheads, wide nostrils, heavy eyebrows, hairy bodies, stooped sholders and knuckles almost dragging on the ground.
I think that I'd need some proof, that it was impossible for there to have been breeding communities of Neanderthal - Cro-Magnon cross breeds, before I am convinced that certain people of today are not carrying the genes of both species.