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.

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"The causes could be the internet, diminished physical fitness, endocrine disruptors, social norms, etc. etc. "

IMO for the post-2014 collapse, it's lumbar flexion caused by smartphones, followed by the fragmented dating market resulting from smartphones' Internet ecosystem.

Also, I doubt the population density explanation -Egypt, Israel, and Pakistan seem resistant to the collapse.

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>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.

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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

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> 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.

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Baby simulator are no substitute as they are not alive and can‘t force a cute smile. Meanwhile having a cute pet which needs to be cared for is essentially a baby

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If I'm reading you right, the idea is that a baby simulator promotes fertility by being a terrible substitute, but a pet is such a good substitute that it inhibits fertility instead?

It's possible, but in a simple model that would tend to imply that having nothing would be even better than having a baby simulator.

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


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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.)

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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.

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>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).

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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.

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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.

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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

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Before contraception and abortion, there probably was not much advantage for the religious. So the strong selection for religiousness is fairly recent. Non-genetic causes can overwhelm genetic causes in the short run, but genetics must always win in the long run.

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If the proportion of religious people increases simply because these are the people having children, and their children and grandchildren continue to be religious, so there is no big loss in conversion, then that makes sense. But is the idea that current or future secular people will become religious because they have more of the religious gene? This seems implausible, because becoming religious is very difficult if you are not raised in a religious household. Also, presumably the religious gene is something that can be used in other areas, such as politics.

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My guesstimate is that the religious gene, propensity to have religious supernatural experience or noticing signs in the surrounding world probably leads to increased church attendance and interest in religion to explain these supernatural occurrences

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Yeah, that sounds very implausible. I think genetic religiosity is more about personality and modes of thinking, perhaps it may even have to do with things like conformity, but of course, your environment is what tells you what you have to conform to.

Also, mysticism or believing in supernatural things is completely compatible with secularism and lack of church attendance. In fact, this is what we see today. Many countries in Eastern Europe, for example, have very low church attendance, but relatively high belief in mystical things. Or think of astrology and stone magic hippies, not religious in the traditional sense, but also obviously feeding some kind of mysticism instinct.

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One aspect missing from all of this: people just don't want to have kids if they've got other fun things to do. We have a strong instinct to have sex but a _much_ weaker instinct to have children. You can convince a 30 year old New Yorker to skip Netflix for a chance to get laid but convincing them to have kids is a much bigger ask.

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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?

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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

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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.


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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.

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