Caplan reviews the literature on the effects of nurture, as provided by parents, on the long-term development of children and concludes that they are very modest, at least as long as we restrict the sample to two-parent middle-class homes. (I agree.) Caplan thinks that this makes the case for having more kids. If, for example, your kid's piano lessons have no effect on her except for her learning how to play the piano, then you might as well not bother. Making your kid play the piano is costly in both financial and, often, nonfinancial terms. If it has little effect to speak of, you can avoid that cost. This raises the expected value of having kids.
That is, knowledge about the ineffectiveness of parenting should make you want more kids compared to a world in which you believe that parenting has huge effects. That's because if your costly parenting is ineffective, you need not do it. Hence you incur lower cost. Like so:
The claim is not that everyone should have lots of kids, but that the average person should have more kids. More than what? More than they were otherwise planning to have. If you live in a tiny urban apartment and love fancy foreign vacations, this might mean one kid instead of zero. If you live in a suburban McMansion and love theme parks, this might mean five kids instead of three.In a recent presentation about the book, he challenges the audience to point out what's wrong with the graph. Here's my answer.
We can think of two ideal-typical models of what parenting means:
God: Your child is putty in your hand. You can shape her as you please.
Caretaker: Your job is to provide basics, such as three meals a day and a reasonably stimulating environment. There is nothing else you can do to shape your kid's character or life outcomes. She's just going to turn out the way she's going to turn out.
Caplan argues that the truth is much closer to model 2, and further away from model 1, than people think. I think he's right. But it doesn't follow that you should have more kids.
The problem with the graph above is that it doesn't tell you that expected value is not just a function of price, but also of the benefits you get at that price. And if you move your model of parenting away from the God model, this obviously reduces the expected benefit of having kids. The less influence you have on how your kids turn out, the lower the benefits of having them.
I am not arguing that desire to mould, to coin a proper variable name, is the only reason for people to have kids. But if it plays a noteworthy role, this weakens Caplan's argument. His book is aimed at people who think that parents must exhaust themselves if they have kids, so as to guarantee the optimal upbringing. These are exactly the people that are high in desire to mould. If they didn't want to mould, they wouldn't go to all of the trouble anyway, would they?
Let's think about parents who read Caplan's book and accept his interpretation of the reasearch findings on the ineffectiveness of parenting. Should they increase, decrease, or not change their desire to have kids? Simple: They should increase their desire to have kids if the reduction in anticipated cost brought about by reading Caplan's argument outweighs the reduction of anticipated benefits. If the two even out, they shouldn't change their desire to have kids. If the reduction in anticipated cost is smaller than the reduction in anticipated benefits, they should lower their desired number of kids.
In other words, you could have read the same research as Caplan has, interpreted it the same way, and written a book called Selfish Reasons to Have Fewer Kids.