Charles Murray, Bloomberg View, November 14, 2014

It’s one thing to point out that programs to improve children’s cognitive functioning have had a dismal track record. We can always focus on short-term improvements, blame the long-term failures on poor execution or lack of follow-up and try, try again. It’s another to say that it’s impossible to do much to permanently improve children’s intellectual ability through outside interventions. But that’s increasingly where the data are pointing.

Two studies published this year have made life significantly more difficult for those who continue to be optimists. The first one is by Florida State University’s Kevin Beaver and five colleagues, who asked how much effect parenting has on IQ independently of genes. The database they used, the National Longitudinal Study of Adolescent Health, is large, nationally representative and highly regarded. The measures of parenting included indicators for parental engagement, attachment, involvement and permissiveness. The researchers controlled for age, sex, race and neighborhood disadvantage. Their analytic model, which compares adoptees with biological children, is powerful, and their statistical methods are sophisticated and rigorous.

The answer to their question? Not much. “Taken together,” the authors write, “the results . . . indicate that family and parenting characteristics are not significant contributors to variations in IQ scores.” It gets worse: Some of the slight effects they did find were in the “wrong” direction. For example, maternal attachment was negatively associated with IQ in the children.

There’s nothing new in the finding that the home environment doesn’t explain much about a child’s IQ after controlling for the parents’ IQ, but the quality of the data and analysis in this study address many of the objections that the environmentalists have raised about such results. Their scholarly wiggle-room for disagreement is shrinking.

The second study breaks new ground. Six of its eight authors come from King’s College London, home to what is probably the world’s leading center for the study of the interplay among genes, environment and developmental factors. The authors applied one of the powerful new methods enabled by the decoding of the genome, “Genome-wide Complex Trait Analysis,” to ask how much effect socioeconomic status has on IQ independently of genes. The technique does not identify the causal role of specific genes, but rather enables researchers to identify patterns that permit conclusions like the one they reached in this study: “When genes associated with children’s IQ are identified, the same genes will also be likely to be associated with family SES.” Specifically, the researchers calculated that 94 percent of the correlation between socioeconomic status and IQ was mediated by genes at age 7 and 56 percent at age 12.

How can parenting and socioeconomic status play such minor roles in determining IQ, when scholars on all sides of the nature-nurture debate agree that somewhere around half of the variation in IQ is environmental? The short answer is that the environment that affects IQ doesn’t consist of the advantages that most people have in mind–parents who talk a lot to their toddlers, many books in in the house for the older children, high-quality schools and the like. Instead, studies over the past two decades have consistently found that an amorphous thing called the “nonshared” environment accounts for most (in many studies, nearly all) of the environmentally grounded variation. Scholars are still trying to figure out what features of the nonshared environment are important. Peers? Events in the womb? Accidents? We can be sure only of this: The nonshared environment does not lend itself to policy interventions intended to affect education, parenting, income or family structure.

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