Book summary: Selfish Reasons to Have More Kids

Bryan Caplan’s Selfish reasons to have more kids: why being a great parent is less work and more fun than you think was recommended to me as a strongly-science-supported take on childrearing. I found it valuable; here are my take-aways.

TLDR: Variation in parenting (within reason) has no significant long-term effects. So take it easy, and maybe invest some of that saved energy in another kid.

The main thrust of the book is:

Nature >> Nurture

I mean, Caplan says it with somewhat more caveats, but that’s the bottom line from his chapters on behavioral genetics. He cites a big pile of twin studies and adoption studies, and tries to answer, for various attributes:

If you’re 80th-percentile on the scale, what percentile should you expect your adopted sibling to be in? How about your long-lost identical twin?

The answers, summarized:

Attribute Adopted sibling’s percentile Identical twin’s percentile
Life expectancy ~50 58
Health (self-reported) ~50 56-65
Health (objective) ~50 56-65
Dental problems ~50 56-65
Height (6in above average) ~50 5in above average
Weight (20lb above average) ~50 15lb above average
IQ 51-55 70-80
Misc intelligence ~50 70+
Happiness ~50 67
Education 51-55 75
High school GPA ~50 71
Income 51-55 “about twice as similar as fraternal” (like you’d expect from pure genetics)
Conscientiousness, agreeableness ~55 “unusually large effects”
Political/​religious behavior[1] 56 (not given)
Political/​religious labels 73 (not given)
Filial appreciation ~60 (not given)

And a couple of attributes that don’t fit neatly in to that table:

  • If a kid is born to parents without criminal records, then being adopted by parents with criminal records (vs adoptive parents with no records) raises their chance of getting a criminal record by 1.2% (from 13.5% to 14.7%).

  • Smoking/​alcoholism/​drug use have mixed results. One study shows a moderate-to-large nurture effects on alcohol use, one shows none.

Note that the world is really complicated, and each of these traits has several studies measuring slightly different things, and the whole thing is riddled with quirks and caveats that don’t fit into this table. Does it make sense to separate out marijuana use from amphetamines/​cocain/​sedatives, or is that p-hacking? What about subgrouping adopted children based on whether their biological parents have criminal records? I dunno, man. Reality is often underpowered.

But also… look at all those places where upbringing fails to show an effect. The only nontrivial effects are on (a) how much appreciation they’ll show you, and (b) their political/​religious labels. And that’s without significantly affecting actual political/​religious behavior, meaning the labels are basically just lip service![2]

(Caveat: all of the above is about long-term effects, i.e. effects on the grown children. Environment can have short-term effects on a person’s IQ, income, criminality, and sexual behavior; but it fades out almost completely by age 25, and, for most of those traits, much sooner.)


Anyway. If you accept the table above—pretty much everything you care about is basically nurture-independent—then what follows?

  1. Instead of aiming to be a 90th-percentile parent like everybody else, slack off! Be a 10th-percentile parent instead! Maybe even 5th! (Not a 0th, though: you want to stay within the domains of these studies, i.e. middle-class first-world families. Obviously, if you starve your kid, their body won’t just learn to metabolize the amazing genes you gave them.)

    Take advantage of take-out meals and electronic babysitters! And real babysitters, or a nanny if you can afford one! Don’t worry so much about the kid dying: kids are safer than they’ve ever been, and the chances of death from accidents or homicide are under one-in-a-million per week from years 1-24! (Year 0-1 is, admittedly, several times higher.) Are you stressed out from driving your kid to all their extracurriculars? Drop any they don’t enjoy—in the short run you’ll both be happier, and in the long run it doesn’t matter anyway! Do they enjoy all their extracurriculars? Drop one anyway! The benefits from you being less stressed and irritable will very likely outweigh the fun of whatever you cut.

    Note that the advice to slack off comes from consideration of long-term effects and how, roughly speaking, nothing you do has any. Slacking off in ways that have short-term effects, ways that make your kid’s childhood less happy is, obviously, costly, and you should only do it if it proportionately benefits you. Your kid’s short-term happiness matters, and/​but so does yours!

  2. Okay, so, parenting doesn’t have significant long-term effects; but you know what does? Genes! Giving your kids good genes is worth a lot. And your most powerful tool for affecting your children’s genes is choosing your mate. “Choose a spouse who resembles the kids you want to have,” sayeth Caplan. “The right spouse is like a genie who grants wishes you are powerless to achieve through your own efforts.”

    (Maybe this doesn’t much change your optimization target—the traits I want in my children are pretty much the same traits I want in a mate, except for, uh, sex stuff—but it seems like a valuable frame to have consciously available.)

Everything else

The book’s section on genetics was the part that really impressed me with its thick coating of detailed scientific study. Most of the rest of the book is a smattering of miscellaneous parenting advice, much like other parenting books I’ve read; but I think Caplan’s opinions are more worth listening to than most folks’, so I’ll relay the particularly interesting bits.

  • Consider the long term. When you think about “having kids,” you probably think of the first five years, or maybe the first twenty: those years of immense investment, of six-hour nights, of mental impairment on par with being legally drunk. To be fair, there’s plenty of joy in there too, sure, but it’s definitely a mixed bag.

    You probably don’t think of the benefits you’ll reap over the following thirty years, watching your kids go through life and playing with your grandchildren.

    Don’t forget to weigh that too!

  • Life-giving science. There are a lot of technologies to help you have more/​different kids! We’ve got:

    • in vitro fertilisation ($12k [edit: per cycle, needing on average 2-4 cycles])

    • artificial insemination ($400)

    • surrogacy ($100k [including medical expenses etc.], $20k more than if you were planning IVF anyway)

    • genetic screening (book doesn’t say; a quick google suggests $5-10k)

    • receiving donated sperm ($400)

    • receiving a donated egg ($10k)

    • sperm sortation ($3000 to choose the gender with 75-90% accuracy)

(There are also chapters on how to get grandchildren and whether your kids are good for the world, but everything there seemed pretty common-sensical to me, so summarizing them would feel like a chore.)


About 60% of the book’s value to me is captured in the nature-vs-nurture table up above, and the rest of this post captures another 20%. But the remaining 20%—the quirks and caveats, the citations, the section on grandchildren—might justify reading the actual book!

  1. I’m lumping politics and religion together because they follow exactly the same pattern in the studies Caplan cites. It’s eerie, honestly, and… highly suggestive. ↩︎

  2. Political parties, at least in the U.S., seem very strongly opposed; how can you flip somebody’s label without affecting their attitudes or behavior? Caplan’s answer seems to be that, because most people are only mildly-to-moderately interested in politics, they can bat almost equally well for either team; and maybe highly-politically-active people break this pattern, but are rare enough that they don’t change the statistics much. I don’t know, I’m not fully satisfied with this, but I have no better explanation. ↩︎