Bryan Caplan, an economist at George Mason, is the author of “Selfish Reasons to Have More Kids,” which will be released this week. Mr. Caplan doesn’t believe everyone should have a lot of children. But he does say many parents and future parents should consider having more children than they are currently planning.

Kaitlin Caplan Bryan Caplan, author of “Selfish Reasons to Have More Kids,” with Simon, one of his three children.

The economists at Marginal Revolution — colleagues of Mr. Caplan’s — have debated some of the book’s arguments in recent posts. Mr. Caplan also wrote a related article for The Wall Street Journal last year and commented on the “Tiger Mother” book for EconLog.

Our conversation follows.

Q. My sense of the research on nature and nurture is that both matter. On the one hand, genes clearly matter. On the other, young children of college graduates, for instance, know hundreds and hundreds more words on average than young children of high-school dropouts. That difference is not mostly genetic.

You seem to have a different sense of the research. You write, “Adoption and twin research provides strong evidence that parents barely affect their children’s prospects.” What’s the brief version of how you try to persuade skeptics like me?

Mr. Caplan: The central idea of twin and adoption research is that disentangling nature from nurture is hard. Our intuition isn’t very helpful. Yes, kids of college-educated parents know more words. But why? Maybe their upbringing is the reason, as you suggest. But babies from college-educated families might excel even if raised by high school dropouts, by learning a higher fraction of the words they hear, or spending more time reading.

So what does the twin and adoption data say? Language fits a standard pattern. Consistent with your skepticism, upbringing has a noticeable effect on the vocabulary of young children. But as children mature, this effect largely fades away. The Colorado Adoption Project found, for example, that 2-year-olds adopted by high-vocabulary parents had noticeably larger vocabularies. But as the kids grew up, their vocabulary scores looked more and more like their biological parents’. By age 12, the effect of enriched upbringing on vocabulary was barely visible.

Admittedly, there’s a sense in which upbringing is all-important: If a baby is raised by wolves, he won’t know any words. (There’s also a sense in which genes are all-important: If you had wolf DNA, you wouldn’t know any words either.) But twin and adoption research focuses on questions that are much more relevant for parents: how your child will turn out if you switch to another parenting style.

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Q. One of the better-known findings of the happiness research is that having kids doesn’t make people happier. But you argue that this finding is somewhat misleading. Over the long-term, people do seem to enjoy being parents. You also offer some advice about how parents can improve their short-term enjoyment of being parents. Will you describe that advice?

Mr. Caplan: Happiness researchers consistently find that people with kids are less happy than otherwise identical people without. The result holds up, but there’s a lot more to the story. First of all, the “depressing” effect of kids, while consistent, is small. Married-with-kids is far happier than single-without-kids, but happiness researchers rarely bemoan the plight of childless singles. Second, kids do extremely well by another plausible standard: customer satisfaction. Over 90 percent of parents say they’d make the same decision if they had a “do over,” and over two-thirds of childless adults over 40 say they wish they had kids when they had their chance.

The finding that parents are slightly less happy is actually one of the main motivating facts behind my book. The problem isn’t that kids “ruin their parents’ lives,” but that parents need a little more tranquility and time for themselves. That’s why the evidence from twin and adoption research is such good news for parents: Parents can make their lives better today without making their kids’ lives worse tomorrow.

A few of my favorite specific suggestions:

1. While parents often lose sleep for years, getting kids to sleep through the night is not hard. Real experiments confirm that the Ferber method — let your baby cry in his crib for 10 minutes, briefly comfort him, leave, repeat — works wonders.

2. Improving kids’ behavior isn’t hard either. Experiments confirm that clear, consistent, mild discipline — like putting kids in the “Naughty Corner” — works even on difficult kids. The problem is that if parents stop imposing discipline, kids soon revert to their old tricks.

3. If neither you nor your child enjoys an extracurricular activity, stop doing it. If the alternative is a little more TV or Xbox, that’s O.K.

4. Supervise less. Lenore Skenazy’s Free-Range Kids makes the case better than I ever could.

Q. Yes, you seem to be pro-television, at least in moderation, saying that it can reduce “secondhand stress.” How, and what else can?

Mr. Caplan: In the Ask the Children survey, kids’ main complaint about their parents wasn’t lack of face time, but what I call “secondhand stress” — the fact that their parents were often tired and short-tempered. The upshot: One of the best ways to be a better parent is to give yourself a break. Electronic babysitters like television and video games definitely help: When they take your kids off your hands, they don’t just give you extra time to relax; they makes it easier for you to treat your kids well.

A few other tips for alleviating secondhand stress:

Avoid activities that sound good, but end up feeling like a chore. If you’re tired of soccer, and your kids aren’t dying to play, it’s O.K. to just play casually — or quit.

Make family vacations less ambitious — and don’t be afraid to leave your kids behind with willing grandparents. The “staycation” — taking time off to enjoy local activities — is undervalued.

If you’ve got more money than time, what are you saving it for? Spending a little money on a babysitter, maid, or gardener doesn’t just give you precious extra hours; it makes it easier to laugh at your kids’ funny questions instead of snapping at them.

Q. O.K., let’s end on the positive — what are the selfish reasons to the have more kids?

Mr. Caplan: The heart of my argument: There’s a close connection between how you raise your kids, and how many kids are best for you to have. Most people think that raising decent kids requires decades of unpleasant sacrifices. No wonder they’re tempted to keep their families small — or remain childless. The good news of twin and adoption research is that sacrifice is overrated. Parents are “overcharging” themselves for their kids. And what do economics and common sense tell you to do when prices turn out to be lower than you thought? Buy more. Stock up. Tell your friends.

Modern parents are far from miserable. But the parenting experience can and should be improved. Instead of fruitlessly playing Pygmalion, focus on enjoying your journey together. Raise your kids with kindness and respect. Find common interests. Use discipline not to teach lifelong lessons, but to persuade your kids to treat you and others decently here and now. If you use these strategies, parenting and bigger families really are a lot of fun.

My wife’s first twin pregnancy scared me. How were we going to cope? The next time my wife was pregnant, though, I hoped for twins. What had I learned? I knew about twin and adoption research long before I became a father. But once our first two sons were born, I took the science to heart. Being parents of twins didn’t have to be a chore — and we decided not to let it become one. This got me thinking: If others’ belief in the power of nurture made them want fewer kids, shouldn’t my disbelief in the power of nurture make me want more? It should, and it did.

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