Posted on September 16, 2016

The Long Shadow of the Nurture Assumption

Robert VerBruggen, Family Studies, September 14, 2016

Parenting doesn’t matter much when it comes to shaping a child’s personality, abilities, and behavior over the long run. That was the startling conclusion embraced by Judith Rich Harris nearly 20 years ago in The Nurture Assumption. And it was one I reflected on frequently while reading two new works, Jonah Lehrer’s A Book About Love and Alison Gopnik’s The Gardener and the Carpenter.

Harris relied largely on findings from the field of behavioral genetics. The traditional studies in this field compare various types of siblings–identical and fraternal twins, adoptive and biological brothers and sisters–to sort the causes of children’s traits into three bins: genes, the shared environment, and the non-shared environment. If identical twins are more similar than fraternal twins, for example, that’s assumed to be genes at work; if adoptive siblings are more similar than random strangers, that’s the shared environment. And if siblings are different even though they’re identical twins reared together, that’s the non-shared environment.

The conscious decisions we make as parents–how strict or supportive we are, whether we send our kids to daycare–should show up as the effect of the shared environment. But Harris reported there was little there. Not much has changed: A massive 2015 research review analyzed “7,804 traits from 2,748 publications,” including millions of twin pairs. For about 70 percent of traits, shared environment didn’t seem to do much at all. By contrast, genes were consistently powerful, typically explaining about half the variation in the traits.

Certainly, there are some nuances here. Parents do affect some important things, including social values and religion, which are, respectively, 27 percent and 35 percent explained by the shared environment. (Educational attainment also has an influence from the shared environment, but it’s not clear whether parenting, parents’ money, or something else is what’s making the difference.) No one denies that severe deprivation hurts kids. And genes and the environment work together in various ways, making the classic three-discrete-bins approach somewhat reductive.

But as a general matter, if parents have a big impact, they must have a different impact on each child, because merely sharing the same house doesn’t seem to make kids much more similar to each other than strangers are. Of those two new books, only one seriously addresses this fact.


After A Book About Love, psychology professor Alison Gopnik’s The Gardener and the Carpenter is a breath of fresh air. By page 23, there can be no doubt that Gopnik knows the score and won’t try to explain it away:

[I]t is very difficult to find any reliable, empirical relation between the small variations in what parents do–the variations that are the focus of parenting–and the resulting adult traits of their children. . . . From an empirical perspective, parenting is a mug’s game.

Indeed, the central argument of Gopnik’s book is that we should reject the concept of “parenting” entirely. She notes that even the word is a recent invention, having become popular only in the 1970s (though I would add that the concept of “rearing” children, and anxiety about how best to do so, goes back much further). Her title refers to the idea that parents should see themselves not as “carpenters” aiming to craft something specific, but rather as “gardeners,” aiming to help those under their care flourish, knowing full well that nature will determine the finer details.


If we can’t deliberately mold our children into astronauts or star athletes or even lawyers, then, what we can do is provide an environment ripe for learning and experimentation. Gopnik notes, for instance, that we can provide “scaffolding” for kids’ activities–setting the conditions for “guided play,” such as asking them to sort shapes according to certain rules–and let them explore.


It was no surprise that The Nurture Assumption was in the back of my mind as I read these titles; to this day, it’s the lens through which I view all claims about parenting. I would also like it to be the foundation of my household’s parenting (or at least child-gardening) philosophy, but for the life of me, I cannot get my wife to read it. She’s already decided our son is going to Northwestern.

I don’t think I’ll be recommending A Book About Love to her. I have a feeling it would make her want to feed our son into some sort of homemade Strange Situation Test so we could see firsthand whether we’re horrible parents. But maybe The Gardener and the Carpenter is a good middle ground for couples like us–realistic about the limits of “parenting,” but respectful of what parents really can bring to the table.