I think this remains to be seen. It's possible that certain less individualistic cultures exposed to individualistic modernity will adapt in a robust way.

Jewish culture, Italian culture, Greek culture, Spanish culture - all famed for big families, worshipping fertility, etc etc. They all fell to the demands of advanced-capitalism demands. A couple of generations and that becomes true of any culture: once women are free to decide their own destiny, and educated enough to know there is a world of life options, they want to dedicate less of their time to child-rearing.

It’s about culture, not economic conditions. A number of American sub-cultures that are more educated and wealthy than average (Mormons, Muslims) also have above-replacement fertility rates.

Maybe we ask Mormon and Muslim women what they think of their education, wealth and expected role in those above-replacement fertility rates?

Don’t forget that those societies also impose heavy obligations on men. Are secular women, many of who are stuck both working and raising kids by themselves without men supporting them, happier on average? I haven’t seen any data to suggest that’s true. Indeed, Mormons are happier overall than other groups: https://news.gallup.com/poll/152732/religious-higher-wellbei.... Maybe there’s a big gender gap there but I’m not aware of any data to support that notion.

It is culture but it's not the pro-individualism enlightenment parts of Western culture that made us great. There's so much anti-natalistic culture to fix (and a little bit of economics)

- make housing cheaper

- fix education so people can start their careers and adulthood earlier

- pass safe harbor laws so that parents and feel safe leaving their kids at home, or letting them take the bus

- also economic incentives help, beef up people's social security if they have kids

> fix education so people can start their careers and adulthood earlier

People can only learn so quickly; you're not going to give people a college-level education by age 15. Modern society requires more education to be productive than past societies, but this is at odds with human biology.

> pass safe harbor laws so that parents and feel safe leaving their kids at home, or letting them take the bus

This is only a problem in the US, but birthrates are low in all developed nations.

Some economic incentives might help a bit, but they're not going to have a dramatic effect: people simply don't want to have big families any more. Kids are a lot of work (and expensive, even with those incentives), so people like to have 1 or 2 and concentrate all their attention on those. They don't want 6 kids.

Their reach of wealthy economic conditions is too recent. Give it a couple more generations and you'll see.