The real reason is not this. The real reason is that in the past, religion meant that people saw earthly sacrifices as leading to redemption in the afterlife, w

The real reason is not this. The real reason is that in the past, religion meant that people saw earthly sacrifices as leading to redemption in the afterlife, which meant that having kids was a worthwhile sacrifice (as preached by the church). To this day, people that are more religious tend to have more kids, even when income-matched to non-religious groups. The decline in religion & rise in secularization tends to map pretty well to lower fertility, and it happens to be correlated with rising wealth (which is why we confuse the two all of the time): https://worksinprogress.co/issue/frances-baby-bust#:~:text=Using%20this%20genealogical%20data%2C%20I,in%20less%20than%2040%20years https://worksinprogress.co/issue/frances-baby-bust#:~:text=U.... Big benefits for having kids certainly helps, and you can have baby booms without strong religion (i.e. under Communism), but the perceived payoff has to be there for the parents to make the necessary sacrifices.