Caplan's Selfish Reasons to Have More Kids

CaplanBryan Caplan has a simple recommendation. Have more kids. If you have one, have another. If you have two, consider three or four. As Caplan spells out in his book, Selfish Reasons to Have More Kids, children have higher private benefits than most people think. Research shows that parents can take it easy, as there is not much they can change about their children. He also argues that there are social benefits to a higher population, with more people leading to more ideas, which are the foundation of modern economic growth.

Caplan provides a fun, easy to read book that gives a great, swift overview of his case. This is the book I’ll be giving to parents, grandparents and friends who have heard me go on about twin studies and genetics. I particularly like it that Caplan gives some practicality to the swathes of findings about trait heritability. Caplan brings to life the arguments of the giants on whose shoulders he stands, particularly Judith Rich Harris and Julian Simon.

I felt that the largest shortcoming of the book was that it does not address the third factor affecting outcomes for the child – non-shared environment. While heritability explains some of the variation in a child’s traits and outcomes, and nurture generally explains close to nothing, Caplan does not explore the research into non-shared environment. Instead, he puts the variation down to free will:

So far, researchers have failed to explain why identical twins – not to mention ordinary siblings – are so different. Discrediting popular explanations is easy, but finding credible alternatives is not. Personally, I doubt that scientists will ever account for my sons’ differences, because I think their primary source is free will. Despite genes, despite family, despite everything, human beings always have choices – and when we can make different choices, we often do.

Caplan states that several of his friends call his belief in free will his “most absurd belief”. While I don’t know all of Caplan’s beliefs, for the moment I will agree with his friends. In Judith Rich Harris’s The Nurture Assumption: Why Children Turn Out the Way They Do, she explored what this non-shared environment might be. In her case, she argued for the effect of peers. What bothered me most with Caplan’s take on free will was not that he did not agree with Harris’s suggestion, but rather, his “it’s all too hard” approach. Unlike Caplan, I expect that over the next few years we will add even further to the explanations for how non-shared environment influences children.

When Caplan came to addressing potential reasons why family size has decreased over the last 60 years, I wanted to hear his arguments in more depth. Take Caplan’s take on Gary Becker’s argument that as women now earn more, they have to give up more income to have kids:

This explanation sounds good, but it’s not as smart as it seems. Women lose more income when they take time off, but they also have a lot more income to lose. They could have worked less, earned more, and had more kids. Since men’s wages rose, too, staying home with the kids is actually more affordable for married moms than ever. If that’s too retro, women could have responded to rising wages by working more, having more kids, and using their extra riches to hire extra help.

It sounds neat, but Caplan assumes that the income effect, which would tend to increase the number of children, dominates the substitution effect, which would tend to decrease the number. It is perfectly plausible for the substitution effect to dominate and women to decide to have fewer children, but Caplan does not address this. He might be right, but as there is no depth to his discussion, it is hard to judge the strength of his argument.

Caplan does point out that in the United States, fertility bottomed out in the 1970s. This occurred despite further increases in income and Caplan uses this as evidence against any income based hypothesis. But the people having children in the 1970s are different to the people having children now. For those women who chose to have no children in the 1970s and possibly responded most strongly to the income effect, they did not contribute to the gene pool and any heritable predisposition has disappeared with them. It is the children of larger families that are having children today. Second, the net fertility rate in the United States is substantially affected by recent immigrants.

Caplan’s preferred view on the decline in fertility is that we have gained a small amount of foresight, allowing us to see the negative effects of early childhood, but not gained enough foresight to note the benefits of children when they are older. There might be some truth to this, but I expect that the other factors that Caplan dismisses are also relevant.

One point where I disagree with Caplan is around his statement that men and women see eye to eye on the number of children they wish to have. Caplan considers that this puts to bed any arguments around women having increased bargaining power. While Caplan’s statistic is true in the most basic sense, the number of children that a man or woman want are a function of a number of things. The main one of these is who the other parent will be. If a woman is paired with the man of her dreams she is likely to want more children than if she is married to a guy who showed promise but has gone nowhere. While Caplan notes that condoms have been widely available since the end of World War II, the pill gave women extra power to decide who exactly the parent is. There is some interesting scope for sexual conflict here.

When it comes to policy prescriptions arising from his position, Caplan explicitly opposes natalist policies to increase birth rates. Caplan states:

After natalists finish lamenting low birthrates, they usually get on a soapbox and demand that the government “do something about it.” There are two big reasons why I refuse to join their chorus. First, while I agree that more kids make the world a better place, I oppose social engineering – especially for such a personal decision. When people are deciding how many children to have, government ought to mind its own business.

Instead, Caplan suggests that grandparents replicate the natalist incentives privately. Given this, it is interesting that Caplan drifts into supporting natalist tax credits in his recent Cato Unbound essay (as I have commented on here). I prefer his arguments for the use of private incentives from his book than his more recent encouragement of government action.


  1. I haven’t read either Caplan’s book or Harris’s, so this may be a misinformed comment, but I’ll proceed anyway:

    If non-shared environment is a significant factor, and if non-shared environment mainly consists of children’s peers, then it would seem to be rational for parents to invest in ensuring that their children have the best possible set of peers. Since parents have no a priori way to know exactly which set of peers would be best for their children, they’d presumably fall back on looking at things like the family income level of potential peers. They would then buy houses in nice neighborhoods populated by families at the same or higher income levels, put their children in private schools with tuition levels that act as a barrier against people below certain income levels, and enroll them in summer camps and other extracurricular activities that cater to higher-income families.

    All this costs money, and a lot of it is incremental spending that would be required for each additional child. For example, imagine a family with four or five children all enrolled in private schools, at a cost of $10-20K tuition per child. If the argument above holds true (and it does seem to mirror the way a lot of families think and act) then in practice the cost-benefit ration for having more children wouldn’t seem to be as favorable as Caplan claims it is

  2. Thanks for your comment dev. Unfortunately, Harris’s idea is not so easy to action. If it was simply a case of putting your child in the better school, we’d expect to see some of that reflected in parental influence on outcomes. Instead, Harris suggests that it is factors such as the child’s relative position to their peers that matters – are they, say, the leader or the joker in their peer group? Putting your child into the best school might not work as when they are surrounded by other high performing children, they may be out-competed for the role of the leader or brain. They might have more of a chance to develop that skill or trait when surrounded by slightly less accomplished peers (although, this is not suggesting that there are no benefits to sending your child to a school where they won’t be shot).

    I understand that Harris takes this group socialisation theory further in her second book “No Two Alike” (which I haven’t read).

    1. Ah, thanks for the correction. As I said, I haven’t read Harris’s book so I didn’t think of this particular twist on things.

  3. “It is the children of larger families that are having children today.”

    It may be helpful to take an ecological view. Imagine two populations, one natalist and accepting material misery, the other having few children that live abundantly. So long as the standard of living of the former is not below Malthusian minimums, and the latter population has some children, the two populations can co-exist in a way that is sustainable, if not eternally, at least for a very long time. The pattern will see the proportions of each population shift relative to each other, but if material abundance makes it possible to defend that lifestyle, the disparity can be great and yet endure.

    The modeling of leader-follower systems suggest that is abundance is a benefit of leadership, while the natalists are followers, that the key to sustainability for this system is ideological homogeneity. The more homogeneous preferences are, the more followers each leader can guide successfully, and the more this kind of disparity can be sustained.

    So long as members of each group need each other in some way; that is, they are interdependent, the natalist component will not inevitably prevail coompletely.

    Moreover, one way for a system like this to self-correct is for there to be some threshold that is necessary to defect from one group to the other. If there are too many poor natalists and that lifestyle brings one too close to Malthusian minimums, some can defect to the abundant infertile category; if there are too many abundant infertiles and they are losing critical mass in the population to be relevant, they can defect to the poor natalist category.

    A two population system with a slow but steady trickle from the natalist camp to the abundant infertile camp can be sustainable not just in the short run, but in the long run.

    1. Thanks for your comment ohwilleke. In your two population scenario, another consequence, besides shifting proportions of each type, is overall population growth. Adding in defection, while changing the number of phenotypic natalists in the population, would not change the result that any natalist genes will still work their way to fixation. Rowthorn’s paper from earlier this year (blogged about by Razib here) explores a similar scenario.

  4. Rowthorn’s paper is incorrect, and obviously so, if natalists need people who are not natalists to survive for some reason. For example, if natalism gets in the way of accumulating the skills necessary to maintain Malthusian minimum levels of sustainance for natalists, natalist genes will not work their way to fixation.

    Of course, the case that natalism has a strong genetic component at all is very weak, given that almost uniform evidence from the history of economic development of high fertility societies shifting across the board to being low fertility societies in a generation or two. In these societies year of birth is dramatically more effective at predicting lifetime fertility than ancestral fertility.

    Also strongly arguing for the case that natalism is not genetic is the fact that there are historical shifts in both directions of the ratio of high SES fertility to low SES fertility. There is no steady trend one way or the other.

    Any time a model predicts something that should have come to pass long ago and hasn’t, something about the model has to be deeply flawed.

    1. There is reasonable evidence, such as from twin studies, that the heritability of fertility tended to rise after the demographic transition (as is discussed here). However, Rowthorn sidestepped this by making religion the heritable trait and having fertility as a cultural implication of religiosity.

      In the short length of time since the demographic transition (5 or 6 generations) and the even shorter time since the bottoming out of fertility rates, Rowthorn’s paper is a reasonable match of the evidence. In the United States, those with higher religiosity have higher fertility.

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