One very proximate possible cause not listed here: not having reproductive sex.

Probably this is difficult to track globally. But we know Western young people are having less sex and less PIV sex than were previous generations. Might that just be true everywhere? The causes could be the internet, diminished physical fitness, endocrine disruptors, social norms, etc. etc. but there are about a zillion think pieces about "overarching social thing X" and far fewer about "people of reproductive age doing far less of the actual activity that directly makes babies"

Years ago the historian Thomas Laqueuer wrote an interesting speculative paper about the dramatic rise in population in 18th century Europe perhaps being due to people having more reproductive sex. The rise predated any kind of improvement in sanitation so it wasn't down to lowered mortality rates. He suggested an interesting base / superstructure rationale: in an era valuing "productivity" with the rise of capitalism, "productive" sex became more central in European sexual lives.

Whatever our current mode of production is, it's not really exactly productive in the old way: a lot of the economy is speculative, unreal, meta, mediated, etc. Certainly the sex lives of many affluent-society young people seem to be going that way as well.

Expand full comment

>migrants needed to shore up birthrates

Turns out no, they only make the problem worse. All that happens is they change the demographics of who gets to be born.

The infant simulators thing is also imo better causal within-individual evidence that the role model / fertility culture thing should have some effect.

Expand full comment
Dec 9, 2023Liked by Emil O. W. Kirkegaard

One article that I think about a lot discussed the relationship between density, status and fertility: https://akjournals.com/view/journals/2055/aop/article-10.1556-2055.2022.00028/article-10.1556-2055.2022.00028.xml

Expand full comment

> For an amusing technological solution, maybe we need to give women baby simulators to awaken their dormant maternal instincts.

This one is kind of odd, since there is huge demand for baby simulators (in the form of pets) from women already, but having pets seems to be more of a substitute for having children than a spur towards it.

Expand full comment

I guess we should focus on housing prices instead of income.


Expand full comment

>disposable income has never been higher

You're missing the point. Motherhood has the same Baumol cost problem as all other labor-intensive activities: the opportunity costs in modern society are higher than ever in history.

Disposable income on its own is irrelevant. You have to compare the relative conditionals: (Income | no-kids) vs (Income | kids).

Expand full comment

I do think that disposable income is a very important factor, but not in the sense that people don't have money to buy food for their children, but rather in the sense that because work pays more today, there is a huge opportunity cost for caring for children instead of going to work, combined with the fact that people care about their relative economic position and having more children than their peers will make them poorer.

Think of people as living in households, because they do, and their income as the household's income. Each person in the household who does not work and does not have any other form of income, divides the household's income without adding anything, obviously this is what children do. Mothers who do not work outside the home for an income also have the effect of dividing the household income without bringing in income.

So think about Bob and John, they work in the same factory and earn the same income, 60 thousand a year. Bob has no children and is married to a female co-worker who also makes 60 thousand a year, so Bob's per capita household income is 60 thousand. Meanwhile John has 4 small children and is married to a stay-at-home mother, so John per capita household income is 10 thousand. John household is poorer than Bob. I think this partly explains why fertility is so local, why people seem to follow local trends. Why immigrants converge to native fertility, but not necessarily all the way, because they also live among themselves often. Why different groups in the same US state seem to have more or less fertility and so on.

Expand full comment

Robin over at Overcoming Bias has some posts on the fertility crisis as well https://www.overcomingbias.com/p/honing-fertility-fall-theories

Would be interesting if you two could get together and discuss this.

Expand full comment

If religiousness was a fertility advantage due to its natalistic ideology shouldn‘t we all be religious right now due to heritability of religiousness (0.5)? Since when do religious groups have a fertility advantage? And could environmental cultural effects of decreasing mortality salients and technology explain the religious decline, while we become genotypically more religious?

Maybe mutational load since the 1870s has caused us to deviate from the religious healthy norm and become more atheist. What do you think? Great post btw

Expand full comment
Jan 6·edited Jan 6

There seems to be a significant control variable missing in the density study, which is access to abortion. This can be hard to estimate where abortion is illegal, of course, but it stands to reason that legalizing abortions and including them in public health care/health insurance systems would make them significantly more common.

The reason why I think this is important is that abortions have served as a means of contraception in many countries where hormonal birth control has been unavailable (i.e. Soviet Union) or illegal (i.e. Japan until fairly recently). Not taking this into account makes it seem like the Soviet states, for example, experienced declining fertility rates since the mid 50s in the absence of easy access to contraception. But what actually happened around 1955 was that the Soviet government enforced a very liberal abortion scheme on the entire Eastern Bloc.

For First and Second World countries, at least (I haven't looked into the Third World), peak post WW2 fertility correlates extremely closely with the year that *either of* abortion or hormonal contraception was made legally available.

This does make me wonder if any "contraceptive/abortive" society is doomed to go extinct; that removing the link between regular sexual intercourse and regular child births is what makes it possible to go below replacement levels and stay there. As long as this link is not removed, might it be that sex drive alone would ensure that most women have at least a couple of children?

Expand full comment

Any thoughts on fertility being higher for men and women with tertiary education than for those with lower education in Finland? https://www.stat.fi/til/synt/2018/02/synt_2018_02_2019-12-04_tie_001_en.html

Expand full comment

I highly recommend Arctotherium's convincing argumentation on the Baby Boom being a marriage boom that came about because of an increasing gender pay gap. Young women could achieve status by attaching themselves to young men.


If you want to increase fertility, increase young man–young woman wealth inequality. (That typed, a shrinking population is fine, in some ways even desirable, if you don't let in foreigners, but that's a separate topic.)

Expand full comment

Regarding role models and national culture, this paper estimates that telenovelas caused a 7% reduction in the probability of giving birth in Brazil over an 11-year period.


Expand full comment

I've suspected for a while that pop density reduces fertility. Beyond the expensiveness of living space, which is the plausible, mechanistic answer, it may be that environmentally sensitive types unconsciously adjust their fertility to density. I'm imagining a metropolitan malaise vs a rural impetus.

Expand full comment

That was soo interesting. Just the right length, just the right level of difficulty (for me). Terrific.

Expand full comment

I'm going to pushback on the income hypothesis.

No country has actually tried paying people to have kids. We have only seen two kinds of support:

1) Some pathetic payment that adds up to 1% of the total cost of raising a child that we all pretend is a big deal.

2) A bunch of in-kind services that are expensive but parents may not even want.

An example of in-kind services are subsidized daycare (what if the mother wants to raise her own children) and public education (what if someone wants to educate their child in a different manner then the state).

We all know the highest fertility people around us are SAHM who prefer private religious/homeschool. Yet there are essentially no subsidies at all for this lifestyle even though you still have to pay taxes for all that other "free" childcare.

I'm convinced that if we just paid parents $300k/kid or so they would have kids. There are a million ways you could do this and it's not that hard to structure it so that high earners and married couples get more and babymamas get less.

I also think a straight up school voucher (including homeschool) would do a lot for fertility while costing the system nothing extra compared to the status quo.

The main thing is to make a single breadwinner many kids household competitive with double breadwinner few to no kids households for all the scare goods in our society (real estate, etc). People who have kids shouldn't feel like they are falling behind people who didn't. Right now "don't have more kids" is a kind of hedonistic cheat code where you consume now and somebody else's kids care for your in your old age via entitlements.

Expand full comment