> the much longer work of child-rearing: who pays for that?
I've been thinking about this, and I have a thought for a stable social system with some historical precedent. Basically, the current educational/career trajectory of most first-worlders (which, in general, I think is a pretty good idea) basically rules out having kids until you've graduated college. Beyond that, most people in their 20s right now don't want to have kids until they're financially stable, which can easily take another 5-10 years. So you have a lot of women who start having children in their 30s, if at all. Basically all research indicates that there are non-negligible risks to both mother and child associated with waiting this long. Genetic defect rates and physical complications from pregnancy are vastly lower in the late teens/early 20s.
So, what if instead, we did kind of a generation-skip thing where (financially stable) grandparents were the ones who actually raised their children's children? This would be a bit of a throw-back to multi-generational households where the elderly (by historical standards) assisted with child rearing. It seems like this would simplify a lot of things economically and career-wise.