My simple model of fertility decline

My core model is both simple and depressing.  Fertility rates have declined around the world because birth control technologies became much better and easier to use.  And people — women in particular — just do not want that many kids.

I do understand that better birth control happened a long time ago, for instance birth control pills become widely available in the wealthier countries in the 1960s, or sometimes the 1970s.  Nonetheless the diffusion of new technologies can be very slow, and for norms to shift it can take generational turnover or even a bit more.  Plus “fertility contagion effects” take a long time to work their way fully through the system.

Those long lags may be difficult to swallow, but social science has numerous examples of very long operative mechanisms.  (Just think of how long it took potential migrants to exploit open borders, for instance pre-WWI.)  Furthermore, fertility rates have indeed been falling for a long time in the wealthier countries.

So a lot of women, once they face the realities of the stress and trying to make ends meet, want only one kid.  You end up with a large number of one kid families, some people who never marry/procreate at all, and a modest percentage of families with 2-4 kids.  There are also plenty of cases cases where the guy leaves, self-destructs, or never marries, after siring a single child with a woman.  That gives you the fertility rates we are seeing, albeit with cultural and economic variation.

Richard Hanania considers why income is not the driving force behind the decline, and why the decline is continuing.

Part of this model is that many women just love having a child.  They love “children” so much that a single child fills up their needs and desires.

I see a similar mechanism in my own life.  I very much enjoy having Spinoza around the house, but I have zero desire to take in another canine.  Whenever I want more “dog attention,” I can assure you that the supply is highly elastic.  Similarly, a single kid can take up a lot of your time and affection, again supply is elastic from the side of the kid.  Maybe parents learning how much they can enjoy a single kid has been another cultural lag?

Under my preference-driven model, fertility declines are very difficult to reverse.  I believe that is also consistent with the evidence to date.

So this is a problem we need to worry about.  The asymptote is rather unpleasant, and the path along the way involve less human well-being, possibly less innovation, and maybe some major fiscal crises as well.

As Arnold Kling would say, “Have a nice day.”