In January I said:

In October I reviewed explanations for the clearly-maladaptive demographic transition, whereby societies consistently have fewer kids as they get rich. I leaned toward:

Lower … acceptance of childbearing and motherhood as measures of the status of women.

On a recent long drive, Bill Dickens and I developed an intriguing elaboration of this theory. The key idea: farming pressures strengthened a fem forager tendency to, when personally richer, invest more energy in pursuing status, relative to raising kids. So when all fems are rich, they all invest more in status, relative to kids, and fertility falls.

Ok, now for the details. When men vary in status and mating can be covert, high status men have two kinds of mates: a few “overt” mates, whose kids will inherit much of his status, and many “covert” mates, whose kids won’t inherit his status and who may have their own overt mates. While a top man will want as many covert mates as possible, he will be choosier about overt mates, wanting them to seem high status, to raise the status of his overt kids. Women will want to be overt mates of such top men, so that their sons can have a better chance to be top men, and then get many covert mates.

Given such status-varying men, women must choose how hard to try to become an overt mate of a high status man. A big part of this effort will be investing in status markers, such as abilities in music and art, good taste in clothes and food, travel experience, etc.  In addition to helping her attract a good overt mate, such status will also help a woman attract better covert mates, and protect and support her kids. Our theory doesn’t much care what exactly are these markers; the important thing is that markers take time and effort to achieve, in addition to raw ability, time that isn’t spent raising kids.

But raw abilities, i.e., an initial endowment of genes, parental status, property, etc., matters as well. There is no point in trying hard if you don’t think you have the raw abilities to make it work. So how much effort a woman invests in developing status markers should depend on her own private evaluation of her raw abilities. Energy not devoted to developing one’s status in the hope of attracting a top overt mate can be spent creating and raising kids via the best overt and covert mates one can find. Our theory doesn’t care what exactly are the indicators young women use to guess their raw abilities, as long as such indicators look stronger when she is richer, healthier, etc.,

Now if all a woman’s status marker efforts were realized by the age of sixteen, with no further hope of improving her markers, there’d be no point in waiting much longer to start having kids. But if a woman can continue to develop her markers for another decade or more, then she would face a difficult choice: give up now and start having kids with the best man her current markers can currently attract, or continue to develop herself in the hopes of attracting a better man later. The better her raw abilities, the more she might be tempted to wait. While a top man might be willing to gamble that a promising young woman will realize her apparent potential, basing his choice on the makers she has so far developed, he might prefer to play it safe and pick a somewhat older women who has more clearly realized her promise.  With age, status markers become clearer signals of raw ability.

We can model this as a one dimensional signaling game, if we think of raw ability, effort, and status marker level achieved all as one-dimensional parameters. A woman would privately see her raw ability, choose a matching effort level, and these would together determine her status marker level. Standard one-dimentional signaling models then make an important relevant prediction: signaling incentives distort actions most for the best agents, and not at all for the worst agents. Translated to our context, the prediction is that women of low raw ability put much less effort than high ability women into developing status markers. So if all women had enough food to feed their kids, high ability women would have fewer kids, who being higher status would produce more great-grand kids.

Now all of the above applies equally to forager, farmer, and industry era woman. But the low fertility of the demographic transition seems to be quite non-adaptive behavior evolutionarily, at least if current wealth levels continue for a while.  So to predict this anomaly, we need to posit some sort of adaptation error; something must be going wrong.  The error we posit is that women’s evolved machinery to manage this status effort problem failed to consider the possibility that societies could get much richer as a whole, and stay that way for a long time. That is, when estimating her personal raw abilities to achieve high status, and hence a top man, a woman may look at her own wealth, health, etc., but does not sufficiently consider the long-term average wealth, health, etc. in her society. If forager societies did not vary much along such lines, there would have been little reason to evolve status seeking behavior that depended on this context.

We thus conclude that as societies as a whole have gotten much richer, healthier, etc., unconscious female status-seeking machinery has been fooled into thinking it has a good chance at attracting a top overt mate, and the large reproduction gains that represents. After all, by ancient standards women today live in magnificent palaces on luxurious estates.  This mistaken judgement is apparently confirmed when women see the impressive status markers held by the men they can attract. So women have been fooled into investing greatly in status, far more than their real relative raw abilities can justify; they can’t all get a top overt mate.

Now the fact that foragers lived in bands of 30-50 overtly egalitarian folks limited the reproduction gains from being a top man, and hence the gains from being the overt mate of such a man. But farming introduced much denser living, explicit class hierarchies, and often explicit larger harems for very top men. This greatly increased the gains to women from being the overt mate of a top man. We posit that some free parameter in unconscious female status-seeking machinery, a parameter describing the magnitude of status gains, has evolved over the last ten thousand years or so.  That is, with farming women evolved to more eagerly seek status when of high raw ability.

In sum, Bill Dickens and I posit that farming fems learned that, compared with foragers, farm fems get larger reproductive gains from being an overt mate of a top man; her son might then also be a top man with many covert mates. Bill and I also posit that unconscious female status-seeking machinery never learned that when estimating their chance of achieving this end, they should attend not only to their own personal wealth, health, etc., but also to the long-term average levels of such things in their society.  Before the industrial revolution, societies just never varied enough in such things to make this attention pay off. Now when industry has suddenly made everyone rich and healthy, women unconsciously assume they all have a big chance at attracting a top man as an overt mate, if only they invest enough in accumulating status markers. So women in rich societies invest more in status markers, and wait longer before giving up and having kids with the best overt and covert men they can find. Hence the demographic transition: fertility falls as wealth rises.

What about men?  Much of this analysis also applies to men. Men also have raw abilities, must put in effort to convert abilities into status markers, and resources used this way reduce resources to support kids. Unconscious male status-seeking machinery may also fail to consider society’s long-term average health, wealth, etc. when estimating a man’s chance to gain high status and many covert mates. So men today may also devote excess effort to developing status markers. The main differences seem to be that 1) men tend less to directly raise kids, 2) men can father kids at older ages, and 3) men gain more reproduction from being high status.  So men should work even harder to gain status markers. But even so, raising overt kids will less distract men from pursuing high status, and a man’s delay in starting kids will less reduce his fertility.  Thus excess male status efforts probably do less to reduce overall fertility.