The (Fake) Long Decline of Fertility - Lyman Stone
Lyman Stone
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The (Fake) Long Decline of Fertility<br>There are three fundamental forces shaping fertility in the long run... and also cell phones
Lyman Stone<br>May 19, 2026
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Once again, the internet is being brainfried by a Statista chart. As a reminder, if you share a chart in the Statista color scheme, I downgrade my view of your general ability to learn and pick up new information. This heuristic has always served me well, until today, when Tyler Cowen , whom I admire enormously, shared a Statista chart!! Oh no!!
I have already thoroughly debunked this chart in the last.<br>This post is free, but you should subscribe anyways, because I’m such a nice guy.
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But in this post, I’m going to try to provide a simple model of how long-run fertility change works, and why it shows that new digital technologies shifting the value of solo-leisure vs. social-leisure may indeed have a big role to play in fertility dynamics.
The Three Big Parts of Long-Run Fertility Change
There are basically three main elements of long-run fertility change. This is not to say that other things don’t matter, but we can conceptualize fertility change in three components and, when we adopt that conceptualization, my own experience has been that new information is very easy to incorporate with minimal creativity or rationalization.<br>The three big factors are:<br>Selection pressure via mortality and replacement
Recurrent emergence of cultural valuation of selfishness
Changing cost of fertility and especially intergenerational wealth transfer dynamics
We will very briefly take these in turn. I want to emphasize that I will be citing sources very lightly because my theses here will mostly be on not-terribly-controversial grounds. “Mortality drives cultural selection” isn’t groundbreaking stuff if you know the history of warfare and illness. “Having kids is a costly choice” won’t blow your mind. “Caldwell’s intergenerational wealth transfer hypothesis is basically correct” should surely be well understood by now, especially given all we know about child labor laws, school expansions, and fertility. I’m rehashing stuff here that good demography students learn, memorize, and can recite in their sleep.
Mortality Pressure
The fundamental force shaping human history is death. People die. Cities die. Civilizations die. Death is how we are selected for. Human genetics show extensive signs of major selection pressures over the last 12,000 years, and those signs point a giant boney finger to a long-running history of enormous epidemic and nutritional stress, as well as strong preference for people who are broadly competent and functional in the world. The key vehicles for this selection are differential fertility and mortality, but the preponderance of selective sweeps impacting genes related to nutrition and immunity strongly suggests mortality has been the dominant selection pressure in human history.<br>We are who we are because the people not like us died off in whole lineage groups.<br>This being the case, historic humans simply had to have a lot of kids. “Quality vs. quantity” tradeoffs simply couldn’t have been a concern because they were running on a mass death treadmill. For a breeding pool to survive (which is to say, an endogamous group, or what we would call a “culture”), they had to have a lot of kids.<br>Because endogamous groups very very often correlate with political structures like villages, tribes, cities, states, dynasties, empires, etc, this process easily became a collective action opportunity. Mating, marrying, and breeding norms were essentially political products. Romans kill unwanted daughters, Egyptians don’t. Jews marry one way, Greeks another. Political leaders were analogized to parents, and in the most primordial states in Mesopotamia and China, we often see evidence of fertility cults at the center of political organization. Keeping ahead of the specter of social death was a central concern for many historic cultures.<br>Thus, mortality pressure created a disciplining force which motivated kinship groups to prioritize reproduction. We see this even in modern contracepting societies: when a child dies, parents often accelerate the next birth as a form of “replacement fertility.” It really is the case even in modern data that eros and thanatos are closely linked.<br>This matters for the interpreting the long-run graph, because if societies basically target surviving fertility, and if some societies do this via marriage regulation, some via abortion, some via contraception, and some via infanticide or child mortality, then measures of “live births” will be misleading. Some of those live births get killed very quickly. Instead, we want a comparable cross-cultural measure. For that, we need surviving fertility. Here’s surviving fertility for the U.S.:
I’ve highlighted the periods of clearly declining fertility. And here’s the same, but with the linear...