Fertility Fall From Selection Neglect

In the novel Pot Luck by Zola, a middle class woman in 1862 explains why she had only one kid, Marie, & wants Marie to have only one kid:

‘Children, you know, are such a burden.’

‘Indeed they are,’ remarked Madame Vuillaume. ‘If we’d had another one we would never have been able to make ends meet. So remember, Jules, what I made you promise when I gave you our Marie: one child and no more, or else we’ll fall out. It’s only the working classes that have children as hens lay eggs, regardless of what it’ll cost them. It’s true, they turn them loose into the street like so many flocks of sheep. I must say it makes me quite sick.’

Marie gets pregnant again, and then her mom disowns her.

Selection effects are often powerful, simple, and yet neglected. Neglect of selection effects arguably accounts for people mistakenly overestimating investment fund returns, accepting typical claims of significantly significant empirical estimates, preferring views for which we seek confirming but not disconfirming evidence, thinking that a beautiful and congenial universe must have a creator, thinking that seeing an empty universe implies that little of it by volume is now visibly changed by aliens, judging most winners of recent wars to have been on the more morally virtuous side, seeing docs of young patients who get better as effective, and thinking that schools make students into better workers.

In my life I am personally struck by how often I have been truly surprised to learn of selection arguments. Even though they tend to be quite simple and persuasive, many just didn’t occur to me before I was told of them. Selection neglect thus seems to me one of our most plausible candidates for a cognitive mistake that can greatly distort our thoughts and actions. It seems that evolution just didn’t bequeath our minds with strong natural abilities to notice and correct for selection effects. This each individual must learn anew, and usually fails to learn. 

Our world fertility decline looks pretty clearly biologically maladaptive, and so to explain it we need to posit some sort of evolutionary mistake, showing how our ancestors could have plausibly evolved a habit that then went so very wrong in our unusual recent world.

I’ve previously suggested that, for our ancestors who had a shot at they or their kids becoming high-fertility kings or queens, it made sense to invest less in current fertility and more in acquiring more better status markers. While this heuristic should have triggered on having high relative status, it might have actually triggered on high absolute wealth, as wealth was a consistent sign of status and median society wealth rarely varied much before the last few centuries. Thus plausibly explaining why we now all cut fertility as we all have gotten rich.

Let me now instead suggest a different mistake theory to explain our fertility fall, in fact a selection neglect mistake theory. This theory starts by accepting Henrich and Gil-White’s story that in humans prestige functions to focus our learning and emulation efforts; we prefer to copy the beliefs and behaviors of those who seem successful overall as indicated by many features, including their success at getting others to copy them. 

Most of the time this works pretty well, as the behaviors that tend to be found more often among the more successful do in fact tend to promote success, relative to alternative behaviors. This is, in fact a big Secret to Our Success, in the words of Henrich’s popular book title.

But sometimes selection effects can make behaviors appear more often among those who seem more successful, even when such behaviors do not on average cause more relevant success. For example, a survey of business people who went far from low rags to great riches should find that at some point most of them took big risks, and did so repeatedly. Compared to others, the top tail of the richest newly-rich folks will more often have big risk-taking as part of their story. Yet on average most business folks would be worse off if they took such enormous risks. Thus business folks who just naively emulate this particular behavior of the most successful business folk around them will be making a selection neglect mistake. 

Similarly, hopeful junior academics tend to notice that, earlier in their careers, the most successful academics around them pursued unusual and distinctive research agendas. At least the stories told about such successful academics tend to emphasize such moves, even if they weren’t representative. Junior academics might then be fooled by selection neglect into taking such big risks, not realizing that most modestly successful academics got there via pretty boring and low-risk research. 

Such selection neglect can also distort the fertility choices of parents with substantial capital to either bequeath directly to their kids, or to invest in promoting their kids’ success. When such parents choose to have fewer kids, they can allocate more capital to each kid, and then those kids will tend to be individually more rich or successful. So if people look at the more successful individuals around them, and ask what their relatively rich parents did to help make them successful, they will tend to see stories of parents who had fewer kids. 

Now if observers had instead considered a cohort of ancestors, and asked which of them had the most great grandkids or later descendants, they’d probably find less success among the ancestors who chose to have fewer kids. So this selection neglect mistake theory requires that observers look less at this, but instead focus on the behaviors of the parents of the most successful kids. Which are typically easier to see. 

So if humans evolved a habit of trying to copy the behaviors of their most successful associates, and then found that the parents of rich successful folks tended to be rich and to choose fewer kids, people might have also learned to have fewer kids, at least when they saw themselves as sufficiently rich. And as shown in my last post, we’ve seen consistent reports through history of this sort of behavior among rich elites, done explicitly for this sort of reason. Making this a plausible explanation for low fertility among rich elites through history. 

Of course we still need an explanation for why this consistent elite low fertility recently spread to most of the world population, when it did not often so spread in ancient societies. For this, I’ll again postulate that humans encoded this behavior as something that mainly makes sense for parents who are relatively rich and high status, but not otherwise. And now most all of us see ourselves as rich and high status in this relevant sense. Either because we do all in fact have enough capital to make this relevant, or because the “rich enough” condition in our heuristic was encoded in terms of some absolute personal prosperity level.