A lot of who you are is in your genes

September 23, 2009

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A few years ago John Derbyshire made a comment in The Corner which referenced Judith Rich Harris’ argument in the The Nurture Assumption. In a nutshell, Harris points out that decades of behavior genetic research suggest that ~50% of the variation of many psychological and social outcomes are controlled by genes, ~10% by “shared environment” (e.g., parental input) and ~40% remains unaccounted for (usually this is termed “unshared environment”). Harris’ thesis is that this last consists of peer groups. This is a tendentious assertion, but the bigger point of controversy among Derbyshire’s interlocutors in The Corner was that he was downgrading the effect of parents, which is of course a “no, no” due to social conservative emphasis on this particular parameter (Charles Murray came to Derbyshire’s defense).

Consider sex. It is well known that children in single parent households have sex earlier. That teen moms tend to beget teen moms. In the public domain this is often presented as the effect of role models, or the developmental disruption which might occur in a single parent household. In other words, warp the environment, and you warp the outcome. The public policy responses from the Left and Right are manifold. Condoms, more sex education. Better values, abstinence education. Buffer the economic correlates of single parenthood with a more robust welfare state. Strengthen marriage so that single parenthood doesn’t occur. If you have an environmental problem, you have an environmental source of palliation. There’s a problem with this story: it’s probably wrong. Consider this new press release of a recent paper, Genes May Explain Why Children Who Live Without Dads Have Earlier Sex:

The more genes the children shared, the more similar their ages of first intercourse?regardless of whether or not the children personally had an absent father. This finding, the researchers say, suggests that environmental theories don’t fully explain the puzzle. Instead, genetic influence can help us understand the tie between fathers’ absence and early sex.

“While there’s clearly no such thing as a ‘father absence gene,’ there are genetic contributions to traits in both moms and dads that increase the likelihood of earlier sexual behavior in their children,” notes Mendle. “These include impulsivity, substance use and abuse, argumentativeness, and sensation seeking.

“Sensation seeking.” The 10% which is “shared environment” probably has a relatively small effect. I think the answer, if there is any, is in the 40% which is unshared. That poses a problem, because to change outcomes you need to engage in a proactive Kulturkampf. That is more daunting than giving single moms more welfare benefits, or telling them to go to church and instill some values in their children.

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