Poorer, underdeveloped countries tend to have a higher % of rural population, and they're incentivized to raise more kids as they'll later be able to help with the farm work.

Edit: Wtf are these answers

Because eduction and prosperity reduce the brith rate. You don't need that many children to care for you when you're old, if you can expect to get healthcare. You don't shouldn't get accidental children if you're educated about sex and protection. In an educated society you will have fewer children later in your life, because perhaps after school you will also go to university, delaying the moment where you feel stable and settled enough to start a family. The more educated you are, the higher the chance that having children is a deliberate, careful choice, and not just something that happens. And last but not least, politics play a huge role in what incentives you have. Especially for this point, I recommend the Kurzgesagt videos about South Korea and Germany.

• https://www.youtube.com/watch?v=Ufmu1WD2TSk
• https://www.youtube.com/watch?v=n-gYFcVx-8Y

They are dropping in poor countries too. Poor countries tend to have higher birth rates, but they are dropping.

when women have a choice (income, a creer, birth control) they mostly choose 0, 1 or 2 kids.

For every woman who then chooses 0, you need another who chooses,5 just to maintain the status quo.

Lotta things here but poor families are often religious which tells them to have as many babies as possible, lower to no access to birth control and health care, and low paying jobs mean more hands working can provide a little more. People with means and availability typically have less children.

But also in major capitalist countries people work so god damned much they dont want or have time for kids

I saw an interesting thing a few years back (which I can't now find!). It was a plot of energy usage Vs reproductive rates of various animals. The graph produced quite a linear line (more energy expended==>lower reproductive speed). Humans were wildly off that line. At least until you accounted for external energy usage (burnt fuel, electricity etc). That jumped us back to the line.

I'm still not sure if this was just a coincidental result, or pointed to a deeper correlation.

Nuclear anxiety might have also played a role.

Poor people have more kids because their mortality rates are higher, etc.

More importantly is there any citation for this supposed "fact"?