I would hope that loyalty would have nothing to do with it, as I never imagined the alien pregnancy as involving woohoo in the first place. I always saw it as the result of experimentation from a process that was more, well...alien. That we weren't supposed to know how it happened because it wasn't supposed to be possible. My theory has been something more bee and plantlike, due to the use of the word "pollination".
I don't have too many aliens in my game, but I like to set it up so that only the females can "pollinate" human males (impregnate) but it doesn't work any other way. So children have to be born from male Sims and female "fathers". Something about that just makes me happy.
