Partially human instict, partially culture, partially because it's a way to influence the future beyond your own life. The whole thing with kids is yes, it is all of those things. But you have to put someone else above yourself, if you're looking at a kid as "how do they benefit me" you probably don't have a good parental mindset. Personally If I have kids probably just gonna adopt because I'd rather care for a kid who's already here and doesn't have a home than bring a new one in to the world, but also because I can't get pregnant so not like I'm having biological kids. Definitely none till at least my mid 30's though.