Not sure I agree. I don't think there are selection pressures on humans any more. I come from an extremely long line of organisms that had offspring. In fact,

Not sure I agree. I don't think there are selection pressures on humans any more. I come from an extremely long line of organisms that had offspring. In fact, it goes back to the beginning of life forms that could sexually reproduce. Are you saying that many of my sentient ancestors who understood where babies came from didn't actually want kids? It's possible I suppose. But I think my reasons for not wanting kids are less to do with my DNA and more to do with experiences I had during my life. Also, if you're taking about modern changes and their effects on human behavior, what traits do paid sperm donation / surrogacy select for? Maybe the concept of having that choice is new, but lots of people technically have the choice but don't "know it". They follow cultural norms. All of their friends have babies, so they have babies. Has something happened to the DNA of all these Japanese people who don't want kids? Or is it a cultural shift? I'm betting on the latter.