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Emmanuel Florac's avatar

I think there is no single answer, the causes probably vary a lot across countries. However here in France we can see several important parameters : first, jobs. My children are 26 and 28, have master degrees, speak several languages, but still don't have completely stable jobs with decent pay (I mean like even slightly higher than median and/or average). Therefore, they certainly aren't close to having children. Because also second : housing. There is a massive housing crisis, in part because of AirBnB, in part because of insufficient construction, and largely because of the way people (don't) live together : in my town, the number of apartments exploded in the past 20 years, but the number of inhabitants remained exactly the same, just because people live alone more and more. This creates a huge pressure on housing demand, and makes existing home too big (nobody needs a 5-person flat anymore), and that compounds with the poor job status because you need to earn insane money to be able to afford a decent home. My son rents a single room in a squalid neighbourhood for 700€ a month.

So imagine that : a single room costs half of full-time minimum wage, but to rent a place you're required to earn 3 times the price. OTOH median salary for non-management workers is less than 1.5x minimum wage... Therefore at least half the population can't even rent a single room. Now start planning having children on top of that? Yeah, sure.

Headless Marbles's avatar

The opportunity-cost theory is basically Baumol's cost disease applied to childrearing. Part of me wonders how quickly humanity will see a natural self-correction or rebound in aggregate fertility. Intuitively it feels like we are headed for a very sudden selection bottleneck for whatever heritable traits make individuals' fertility resistant to Baumol's cost disease -- like, talk about punctuated equilibrium! In a generation or two (i.e., almost instantly), people whose heritable traits cause them to react to modernity by having no or few kids will fall out of the population, leaving the fertile remainder to radiate rapidly, essentially taking over the gene pool all at once.

I'm sure one could describe this with a system of differential equations given some assumptions about heritability, assortative mating, and so on.

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