"I don't know all the history behind the cultural reasons, or behind the native - drives - but today, humans have romantic impulses that are pretty strongly correlated with sexual impulses, and our culture reinforces it. I don't know if you've read a lot of human fiction, but it tends to revolve around the subject more often than not. We grow up with parents who are usually romantically involved with each other, though not always, mine are divorced now. And being 'successful' at that kind of thing is also a source of status, in many social circles."
"Do you mind if I ask you questions about that? I don't know whether anything I might be curious about is going to be rude to ask."
"So, in human cultures, we're almost invariably certain who our mothers are and usually have a very good guess about our fathers. We use this information for all kinds of things, but the practical one that springs to mind is avoiding inbreeding - we steer clear of reproducing with close relatives, and if we do anyway the kids often turn out badly. Is that not a problem with you? Is it a problem you solve a different way?"
"Sounds workable. Humans also get raised by our parents; what about you?"