Nov 17, 2023·edited Nov 17, 2023

I'm not sure whether you mentioned this in one of your posts on the topic, as I haven't read all, so I apologize if I'm restating something covered before, but it's interesting to note a few ancient societies had a straightforward way to allow for high fertility among elites coupled with status/wealth preservation: limiting inheritance to the first child of the main wife. That one child inherited everything, the others inherited nothing, and thus extraordinarily rich and/or powerful men had dozens, sometimes hundreds, and, on a few instances, even thousands of children (e.g., Genghis Khan).

Nowadays that'd be considered deeply immoral by most to all societies, thus not an option, but it fits with the KAQ hypothesis, after all, no matter how many children a King has, only one will be king. It'd therefore be interesting to check whether the low fertility "mid-range" of "elites-but-not-kings" correlates with fair inheritance laws benefiting all children, thus incentivizing those families to have fewer ones.

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Yes, it seems that giving most inheritance to one kid was selected for among elites, and when it was policy elites were willing to have more kids. But still fewer kids.

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In warlike societies there was/is a huge shortage of husbands. Often the warrior's widow had few or no legal rights to her deceased husband's estate and could be dispossessed. Without a means of support, she and her children would starve. Kings and warlords often acted as the husband of last resort, giving the widow a lifeline. In the Koran for example a man is enjoined to marry as many wives as he can support. King David's harem was likely also predominantly war widows. Without a safety net, not knowing what would happen to their families, warriors would be less likely to rush off to war.

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Do we need new fertility theories? I feel like the ones we have are much simpler and do a great job explaining things:

(1) Education strongly explains what's going on. Education increases income and decreases fertility. That is extremely well documented I think.

How education increases income needs no explanation I think. How it decreases fertility is straightforward:

(a) People almost totally avoid having children during education, and the more years in education, the more of the fertile years are spent almost totally avoiding children.

(b) Education gives people, and especially women, something else to do besides raising a family.

(c) At a basic level (literacy vs. illiteracy), those who are more educated can better control their fertility.

(2) Having more choices also strongly explains what is going on. As income increases, people simply have more choices of things to do besides having children.

(a) Opportunity costs are much higher when you have many alternative options for your time. The lost alternatives (both economic and not) are much greater when a woman has many more choices of what to do with her time, and a richer society affords her many more choices.

(b) We can easily see that when TV or Internet reaches a place, its fertility goes way down. Very simply, people can watch TV or browse the Internet rather than do **the thing.** ;-) It is well documented that fertility increases during blackouts.

These two very old and widely supported 'theories' -- education and having more choices -- nicely explain why increasing income and wealth are associated with lower fertility. We have great theories that are simply and almost certainly true.

Why do we need complicate theories that defy Occams razor? Is it because there is that slight U-shape? That (ever so slight) recovery at the very highest incomes?

I think that slight recovery at high incomes is easy to explain: At the high end of the income spectrum, folks are all about self actualization, and having children is going to part of that for most people. If you are an A-type trying to meet every definition of success, where you check all the boxes, of course you will want kids. For the strivers conquering Maslow's Hierarchy of Needs, skipping kids would be a big oversight. Top politicians, the ultimate strivers in our society, almost always have children.

These are the simplest, Occams-Razor type explanations. Why do we need further theories beyond this when these theories are pretty robustly supported and very convincing?

We aren't very likely to do away with either education or fun alternatives entertainments beyond sex. So what is the solution? How do we get to higher fertility?

The easiest answer is just to value children really highly. You can just decide children are really important, and that should override everything else. That is what worked for Israel. They are extremely educated and full of entertainments. But they just decided, 'we've gotta have a lot of kids or our people are f$cked' and so they do.

Just deciding that children are super important probably seems like too simple of a solution, but it probably really is that simple. The elite strivers (of which politicians are my example) are busier than anyone, and more educated than most. But they have decent fertility just by deciding that is an important part of their complete life. Plus being good strivers, they are great at attaining marriage, which is key to fertility.

The fertility of the religious is due to the same thing. It isn't a mystery. They have a worldview where having children is a key part of a fulfilled life. But anyone can have that worldview. The problem right now is that culture doesn't value parenthood (and its usual precursor) that highly.

Summary: Now that fertility has crashed in high income places, for very mundane causes that we understand well, the solution is not to try to undo those causes, but overcome them by just valuing children more than ever before, the way Israel does.

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I tend to agree with this perspective, and am curious to read Robin's response. The key behavioural mediator is capitalism: the return from applying yourself to education, work, or business is large and scales very, very high. The return from applying yourself to parenting is... constant? Predictable? Often less appealing, at any rate, than pursuing the financial opportunities that the developed world offers. It used to be the case that those financial returns were only available to a small subset of people in society, but we've put a whole lot of work into broadening the base and, well, here we are. Capitalism, equality, population growth: choose any two?

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Nov 21, 2023Liked by Robin Hanson

Sarah Perry has some hypotheses about why demographic transition started in some regions before other parts of the world that had similar levels of economic development and mean years of education per woman.


‘Around the sixteenth century, Europeans west of the Hajnal line began to switch to a pattern of late marriage, with a significant proportion of people never marrying, and uncontrolled fertility within the population who married. This norm was likely not adopted for the conscious purpose of limiting the population, but had the effect of keeping the population somewhat more comfortable below the Malthusian limit (Clark 2009). In preindustrial Japan and parts of China, however, farmers in long-settled areas kept early and universal marriage, but adopted fertility control by selective female infanticide and other means. In these populations, almost all women married and married young, but had around three children during their lives (Jones 1990 at p. 118). With industrialization and agricultural advances offering a pseudo-frontier relaxing Malthusian limits, the Japanese briefly adopted uncontrolled (or at least much less controlled) fertility, but after World War II they began to control their fertility once more. Most existing populations have been through multiple fertility transitions, and each transition has shaped the population.

Almost the entire world has recently undergone a single fertility transformation, one from uncontrolled fertility to controlled fertility. This transformation began in the late eighteenth century in a few small villages in France and New England, and subsequently spread to every continent and almost every population in the world. Europe at this time exhibited both early and late marriage patterns, but uncontrolled fertility was the norm, a crucial part of a memeplex maintained by the Catholic Church and other institutions at the center of every community.

What caused this worldwide fertility transition? Why did it start where and when it did, and what were the mechanisms of its spread? Why did so many humans adopt fertility norms at odds with their own genetic fitness? And what made some societies immune? What follows is a theory for the timing, location, spread, and limits of the modern fertility transition, taking into account the cultural, economic, and reproductive histories of dozens of populations.’

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That link is quite good; thanks for the pointer.

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According to Greg Clark it was the UMC Yeomen farmers and small time merchants/craftsmen that had high eugenic fertility in Europe during the high Middle Ages into the pre-modern period.

These people were expected to earn their livings based on their efforts, not inheritance, and thus division of inheritance was not a big issue for big families.

The nobility by contrast owed their wealth to rent extraction via violent enforcement, and thus more kids meant more division of fixed rents. The UMC Yeomen farmers and small time merchants/craftsmen outbred the nobility.

Fertility problems can't be solved by the elite, they are too few in number. As goes your middle/UMC so goes your fertility. It's important whether they enjoy kids or see them as a burden.

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The reason for the lower fitness of aristocrats was their high homicide rate.

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When you make your money extracting rents via violence you tend to die violent deaths.

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Have we considered whether there's a correlation between number of children and the marginal utility of child labor? When I think about why my grandparents on my mom's side had 7 children the most likely explanation to me is that it's because they were [poor] farmers and more kids = more farmhands. Could higher income or higher GDP be masking either an increased cultural aversion to, diminished need for, or transition away from family businesses requiring child labor (or some combination of all of these) and thus have removed a major incentive for more children?

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> In this case, the evolved heuristic would be to go wild on fertility when you joined this highest status group. Seems like this could work.

Wait, does it? Who is in this highest-status very fertile group then? And wouldn't the "selection neglect" story then predict people would mostly imitate this group and try to be very fertile themselves?

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Building off of "more education/career == shorter fertility window for elites", it seems there is also a curse of optionality at play. Western social hierarchy has diversified into many ladders and it's tough to compare apples to apples when you're dealing with a Fortune 500 C-level versus an actor whose face is on every billboard spanning multiple continents or a senior government administrator. Not only is the mating pool of elites larger, it's harder to resolve the pecking order. This would also apply to non-elites, who - while less mobile - have a pseudo-mating pool via the internet and other mediums of sexual or status signaling.

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KAQ is a fruitful hypothesis because it examines causation, not correlation. Google "declining fertility" and although you get thousands of results they are all the same: basically correlation.

I think that there is a fertility Goldilocks Zone between the very poor to whom another child is another mouth they are unable to feed, and the well-off in white-collar occupations to whom another child is not free labor.

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Still don't understand why any theory is needed. Throughout most of human evolution the strategy: have kids unless the costs to have the outweigh benefits plus desire to fuck worked really well. Evolution equipped us with some innate drive to have kids but it wasn't selected to only be moderately strong because it was balanced against the desire to fuck and usually the economic benefits of having a large family was a good proxy for procreative success of doing so. So evolution could leave it mostly up to our flexible judgement to make the call.

That situation changed with birth control, modern careers and women working out of the home so why is any more theory needed?

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Speculation about the differential fertility among rich and poor goes back a long ways. I particularly enjoy the late-medieval notion that peasants were too tired for sex in the evening due to all the physical labor, and therefore inadvertently ended up having sex during the more fertile period between first and second sleep, in the middle of the night.

It's possible that author (the name of whom I cannot recall, though likely it was not Laurent Jobert, who was still advising sex in the middle of the night for conception in the 16th century) was onto something, though by accident. The signalling might be related to physical exertion outside during the day -- hardworking laborers and warrior elites are outdoors getting a great deal of UVC on their skins (which increases testosterone) and various blue-spectrum light in their eyes (which most strongly entrains circannual hormonal rhythms). It's quite possible that relative wealth is merely inversely correlative to exertion outdoors, which might well be the real factor. Strong, healthy, vigorous men and women who are doing their thinking under the influence of pre-historically normal hormone levels might very well always be willing to add another kid or two to the family.

Note that this would also explain the Amish. Specific high-fertility subcultures like the Hasidim can be seen as motivated outliers -- if it's a mitzvah to have more kids, ideologically motivated people can overcome the effects of less well-regulated hormones.

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An interesting question would be how well KAQ explains other unusual contemporary behaviours, such as delayed marriage/reproduction, increase in female selectivity with respects to mate choice, increase in length and cost of mating rituals, reduction in age gaps etc. That some such as delayed marriage for women seem at least superficially at odds with the usual description of historical elites. Perhaps one must posit some other theory or theories to account for various other maladaptive behaviours.

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For the recent decline in fertility around the world, there is one obvious explanation: lumbar hyperflexion due to smartphone use.

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An interesting question to pursue would be whether this absolute affluence aristocracy effect might be related to Turchin's idea of elite overproduction.

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If we think that autism and related diagnoses to be a kind of status-blindness, is it reasonable to think that they should be increasing in prevalence under this theory?

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