Bryan Caplan is incredulous that twin and adoption studies haven't shaken my belief that parenting and community influences have a big impact on how children turn out. Not only is my belief firm, but it forms the basis for my central argument in Human Capitalism: that class-based cultural differences play an important role in explaining the rise in socioeconomic inequality along educational lines.
Bryan shouldn't be surprised. I'm not saying genes don't matter: I readily grant that they're important. But to rush from there to the conclusion that parents don't matter, as Bryan does, is to get way ahead of what the evidence shows. Let's consider the verdicts of some of the most eminent researchers of the intergenerational transmission of socioeconomic status: Samuel Bowles and Herbert Gintis, Christopher Jencks, and Bruce Sacerdote.
Bryan knows that these scholars are all leaders in the field and all of them are intimately familiar with the twin and adoption studies on which Bryan bases his contrarian views. Yet Bowles and Gintis conclude that genes only account for about one-third of the correlation in income between parents and children. Jencks, meanwhile, estimates that genes account for about 40 percent of the correlation. And Sacerdote, author of a study of Korean adoptees that Bryan relies on heavily, has this to say after surveying the literature on twins and adoptees: “the estimated effects of family environment on adoptee outcomes are still large in some studies and leave tremendous scope for children’s outcomes to be affected by changes in family, neighborhood or school environment.”
Bryan relies exclusively on twin and adoptee evidence to support his belief in "parental irrelevantism." But the fact is this evidence is much more ambiguous than Bryan lets on, and its ablest interpreters find support in it for the importance of both nature and nurture. Meanwhile, other lines of evidence strongly corroborate the importance of nurture: findings on the importance of good schools and good individual teachers for child outcomes, findings that early childhood interventions can have a big long-term influence on kids, and the well-established pattern of income convergence between immigrant groups and native-born Americans as the children and grandchildren of immigrants become progressively assimilated yet still exhibit clear group differences. All of this evidence points to the importance of the childrearing environment, yet Bryan ignores it all.
In short, Bryan's "parental irrelevantism" relies on a tendentious reading of one just one body of evidence out of many. I have my share of contrarian viewpoints, but I'll need much more than what satisfies Bryan to get me to join him on this one.
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