This was by far the most irritating part of the older versions of the game. It really felt like Conquest was going backwards in comparison to the original game. Original game, anyone can breed with anyone. Then Conquest comes around and suddenly that's not a thing.
Viewing post in what Race's cant have children together
I didn't mind that so much, since it mostly just served to underscore how surface level the species are. You bang a slimegirl and a human with blue skin pops out, that kind of ruins the magic for me. I'm more annoyed by the removal of the option for your starting slave to be a sibling. That and everyone getting "aged up."