Prosperity is the most effective form of birth control.
I think it's more complex than that. For all of human history until now, greater prosperity meant greater fertility. In fact, that is true of all organisms.
The question is why, in recent times, we've seen the opposite among a single species?
First and most important answer: birth control. We have decoupled sex from reproduction and one might argue that is a cause, not a consequence of prosperity. I remember telling my mother that it was odd that there were no more neighborhoods like the one I grew up in. She looked at me like I was a complete idiot and said, "Well, you were born a few years before the pill became widely available. Neighborhoods like you grew up in disappeared overnight."
Then there are other cultural factors.
- decreased child mortality
- decrease in family-based economic activity (small-scale farming, artisanal production).
- social security and options for elder care without families
- need for families to put colossal amounts of resources into each single child to ensure "success" (lots of education, primarily, but in many cases other things).
All of those are linked to prosperity, and the first three are both cause and effect in a self-reinforcing cycle.
The last one, though, is more a matter of
scarcity and anxiety about scarcity. Recent studies show that most parents would like to have more children, but they are afraid to for economic reasons.
The modern parenting strategy most commonly recognizes the need to prepare a child to succeed in a
highly competitive world, not a world of prosperity and plenty, and puts huge responsibility on the parent to make sure that they have the resources to propel their child to escape velocity. And since birth control lets couple have sex without children, they can make those decisions strategically.
I think the "prosperity leads to lower birth rates" narrative misses what's actually important in the seismic shift. Prosperity seems to lead to a greater perception of scarcity which, coupled with the availability of birth control, pushes people to limit their reproduction in a way that no organism in the first 3.7 billion years of life considered in times of plenty. It's not just unprecedented in human history. It is unprecedented in the history of life as we know it.
