Book Review: Selfish Reasons to Have More Kids

by havoc

Despite the title, Selfish Reasons to Have More Kids, the “why you should have more kids” part feels tacked-on. The interesting part of the book reviews twin and adoption studies, making the case that parenting style doesn’t matter much in the long run.

The book’s argument in brief is:

  • in twin studies and adoption studies, most variation in how adults turn out can’t be explained by what their parents did. “Normal” variation in first-world parenting (i.e. excluding abuse, malnutrition, etc.) does not affect how people turn out in adulthood very much.
  • parenting affects how kids act while they are kids, but once people move out of the house they bounce back to their “natural state.” (“As an adult, if I want a cookie, I have a cookie, okay?” — Seinfeld)
  • one long-run thing parents can strongly affect is whether their kids have fond memories of them and enjoy having them around.
  • parents should be more relaxed and invest less time in “kid improvement,” more time in everyone enjoying themselves even if it’s by watching TV.
  • discipline is mostly for the benefit of the parents (“keep kids from being annoying around us”) not for the benefit of the kids (“build character”).
  • (the conclusion in the title) since parenting can and should be less unpleasant, people should consider having more kids than they originally planned (i.e. the cost/benefit analysis is better than they were thinking).

Can you tell the author is an economist?

I get annoyed by “nature vs. nurture” popular science writing, and have a couple thoughts along those lines about this book.

Thank you for skipping the just-so stories

There’s a mandatory paragraph in nature vs. nurture articles where someone speculates on the just-so story. Something along the lines of “such-and-such behavior evolved so that women could get their mates to bond with them and hang around to care for children,” or whatever. Bryan Caplan 100% skips the silly evolutionary speculation. Thank you!

Cultural and genetic factors

However, I did find the book a little quick to jump to the genes. In “Appendix to Chapter 2,” Caplan explains that twin and adoption studies try to estimate three variables:

  1. fraction of variance explained by heredity (similarity of twins raised apart)
  2. fraction of variance explained by shared family environment (similarity of biologically unrelated children raised together)
  3. fraction of variance explained by non-shared family environment (the rest of variance)

Caplan (to his credit) goes to some lengths to point out that the twin and adoptions studies are virtually all from first-world countries and typical homes in those countries. For example, one of the studies was done in Sweden, likely even more homogeneous than the ones done in the United States.

Obvious point, I’m sure Caplan would agree: when something correlates with genes, that doesn’t mean “there’s a gene for it.” For example, attractive people have higher incomes; attractiveness is mostly genetic. So one way income can be genetic has to do with your genes for appearance. Most people would find it misleading to say there’s a gene for high income, even though income correlates with various genes. This is a pretty simple example, but it can be much, much more complicated. Look at this diagram for how genes might get involved in autism, for example.

An outcome such as income often involves genes interacting with culture — say, standards of appearance. The ideal genes for appearance change over time and around the world.

But income isn’t just affected by appearance. Who-knows-how-many genes get involved: countless genes affect appearance, personality, intelligence, and then all of those factors in turn affect your income… in ways that depend on your culture and environment. Make it more complicated: there are also genes that affect how we react to certain appearances or personalities. If standards of attractiveness have a genetic component, then you’d expect that there are also genetic variations in what people find attractive, and then cultural variations layered on that.

Genes and culture also interact with what I think of as tradeoffs or “physical properties of the world.” All I mean here is that you can’t combine behaviors and traits arbitrarily, they tend to come in clusters that make sense together or work well together. This seems true to me for both personalities and for cultures. If you slice-and-dice your time or your concepts in one way, then you didn’t slice-and-dice them another way. Some ways of thinking or doing work better than others, some are more compatible with each other, etc. There’s a source of universals here that need not point to genes.

Finally, culture, like genes, gets passed on between generations. A very simple example: if you had a culture that was fundamentally anti-natalist, it would not last very long. And in fact most cultures are very enthusiastic about having children. This is a cultural universal (other than short-lived sub-groups), but just its universality doesn’t connect it to genes; it could be cultural rather than genetic evolution. Humans inherit so many ways of thinking and doing, and so much background knowledge, through interaction with other people, rather than through DNA.

Getting back around to the book. If you do a twin study in Sweden, then you might find that twins raised apart have similar outcomes. But it’s important to recognize that there aren’t (necessarily) genes for those outcomes; there are genes that cause the twins to have (likely unknown) traits which somehow result in those outcomes, in Sweden.

A couple thoughts:

  • This probably doesn’t matter so much for the book’s practical conclusions. Parents can’t change the culture surrounding their children any more than they can change their kids’ genes.
  • But from a wider perspective, it sure would be interesting — and perhaps useful at times — to know the mechanism for hereditary outcomes. i.e. the causality and not only the correlation.

When Caplan says “it’s genetic” I would say that’s true in that there appears to be a Rube Goldberg chain of causality, such that somehow certain genes are resulting in certain outcomes. However, my feeling is that the mechanism matters.

There’s a difference between a gene for unattractiveness/low-IQ/bad-personality (or sex, or race, for that matter) resulting in low income because the world (including culture) works against high income for people with those traits, and saying that “income is genetic.” Does it really feel accurate to say that “such-and-such percent of variation in income is explained by genetics” here, without mentioning the intermediate traits that are genetic, which in turn affect income?

I’m not sure Caplan would really disagree, but I do think the “nature vs. nurture” genre, including this book, glosses over a lot of complexity that kinda matters.

(The mistake is inherent in the phrase “nature vs. nurture”; if you start spelling out the mechanisms, it’s pretty clear that the two interact and the real question is how specifically in this case, right?)

Bottom line, when talking about the “fraction of variance explained by heredity” I’d add the footnote in this physical and cultural environment, because the background reality, cultural and otherwise, shared among families in the study — or even shared among all families on Earth — has a lot to do with which genetic traits matter and exactly how they matter.

More hours spent parenting

Caplan talks a bit about how people spend a lot more time parenting these days than they used to, and mostly blames increased parental guilt (people thinking they have to “improve” their children).

I’d wonder about other trends, such as the decline of extended family ties and the tendency for people to move across the country. If you’ve had a child, you may have noticed that they’re designed to be raised by more than two people. (The fact that some single parents raise them alone blows my mind.)

Missing from the book, I thought, was research into how other social/demographic trends were affecting parenting. More geographic mobility, more tendency toward social isolation, more tendency to need two incomes to achieve a “middle class” lifestyle, etc. — I have no idea which trends are most important, but surely some of these factors go into parenting decisions.

Caplan kind of implies that changes in parenting are almost all “by choice,” due to beliefs about the importance of parenting, and I’m not sure I buy it. It seems plausible to me that changes in parenting could be mostly by choice, but also plausible that they could be mostly due to socioeconomic trends.


The book has several semi-related side trails, which may be interesting:

  • some discussion of safety statistics, probably familiar from Free-Range Kids
  • some discussion of the decades-old Julian Simon vs. Paul Ehrlich “will population outstrip resources” debate
  • editorial in favor of reproductive technology
  • thoughts for grandparents or future grandparents on how to end up with more grandchildren

Child services risk

On the Free-Range Kids tangent, I always wonder about “child services risk,” the risk that some nosy neighbor gets incensed and creates a whole traumatic drama with child services. To me this risk seems plausible.  In the book, Caplan says they let their 7-year-old stay home alone; which seems fine to me for the right 7-year-old in the right context, but I’m pretty sure a lot of state governments say it’s not fine.

I’d sort of like some “child services screwing up your child’s life” statistics to go along with the stats on abductions and drownings. Should we worry about that?

It’s one thing to say you don’t care what other people think, but when people can turn you in and just the fact of being reported creates a nightmare, I can understand why one wouldn’t want to appear unconventional.


I found the review of twin and adoption research interesting (and practical, for parents). Can’t hurt to remember that your kids are mostly going to do whatever they want anyway, once they move out of the house, and that chances are they’ll do a bunch of the same stuff their parents did. Caplan follows through nicely with implications for discipline, family harmony, and so on.

Some of the rest of the book wasn’t as interesting to me; I’ve heard the Free-Range Kids and Simon vs. Ehrlich stuff for example many times before. But you can skim these bits if you like.

Buy on Amazon — I get money if you do!