Let’s talk about Sex

In some settings we see things like half-elves or half-orcs, suggesting that humans and orcs have sex. Cool. I have no problem with that. They're basically the same thing - same size, maybe a bit of extra muscle or a little extra point to the ears. But in settings with a, let's say, wider variety of peoples, would there be interracial/interspecies sex?

Yes. Yes, there would be.

My evidence? The fact that people get caught committing bestiality all the time (relatively speaking).

So I guess I'd like your thoughts - how would that happen between, say, a human and an elephant-person? Assuming the sex is even possible, is procreation? After all, Billy Bestiality can have sex with a snake and not have babies - so, reasonably, the same would be true of Billy Bestiality having sex with Sally Slither-In.

But if procreation is possible... what are the results of that? In pictures, snake-people often look awfully human. Why can't they have kids with humans?

I guess, at its base, my question is - are your different "races" actually different species? Is "cross-pollination" possible between certain races and not others? And if so, what is your explanation for why a dwarf can have kids with a human but not, say, a gorilla-person or a cow-person? (After all, that means that a dwarf is, fundamentally, the same species as, say, that troll, who can also have kids with a human... which means, well... what does a half-dwarf/half-troll look like?)