All you really need to know is that developed nations are home to the highest levels of human affluence that have ever existed, at all levels of society. And yet they have the lowest fertility rates ever measured. So low that they are not sufficient to maintain population size.
But if you go even further, you'll see that fertility actually declines with income in developed nations. It's not until you get to the top several percent of income that fertility starts rising again.
> It's not until you get to the top several percent of income that fertility starts rising again.
Yes, that's what I meant. You could argue about the significance of the top percentage rise in fertility, but if anything, it shows that fertility is constrained by lack of resources in a significant way as well as education specifically.
Presumably because within the budget constraint, the survival rate of many kids will result in a similar amount of kids at the end of the woman's fertility window.
I didn't say it is constrained by lack of resources, I said it's also constrained by lack of resources.
It's probably about whether women are on a career track and, thus, what age they start having children. Poor women generally aren't on a career track. They finish school and start working a job that doesn't require school or much training. So they can (and do) have children pretty early. Rich women do usually go to college, but they meet a future husband there who is on a high-earning career track and are able to start a family relatively early because they don't have to help pay the bills.
What I'm saying, though, is that if you look at the fertility curve[1] you'll see that many middle class families could eliminate one earner and still have 2-3x the income as poor families that have more children. But people are choosing not to do that (well, secular people are choosing not to do that; intensely religious people often do exactly that).
But if you go even further, you'll see that fertility actually declines with income in developed nations. It's not until you get to the top several percent of income that fertility starts rising again.