The Heritability of Cognitive Ability in Families with Low Socioeconomic Status

In February 2008, the Russell Sage Foundation approved a Visiting Scholar working group to study the malleability of intelligence comprising William Dickens (University of Maryland); James Flynn (University of Otago, New Zealand); and Richard Nisbett (University of Michigan). This working group will develop a model of the way in which the environment affects the growth of intelligence and use it to examine the reasons for the historical improvement of IQ scores over the last sixty years. They will also apply the model to transient affects of early education programs for disadvantaged children and the lower heritability of IQ among low socioeconomic status (SES) families.

This award will permit Eric Turkheimer (University of Virginia) to contribute to the work of the group and to pursue his individual research project on SES group differences in the heritability of intelligence. Turkheimer has synthesized results of his own and others, showing that the heritability of IQ between generations is more likely in high socioeconomic status families than in low socioeconomic families. This may be because upper SES families are better able to shape the environment in which their children grow up in order to maximize genetic potential. More of the variation between children in upper SES families will therefore be due to genetic differences compared to the children of low SES families, who may be subject to more uncontrolled environmental shocks to their health, physical safety, financial resources, and family stability. Together, these factors exert powerful influences on the genetic expression of intelligence. Turkheimer will use two large datasets to look at the developmental trajectory of heritability indices in low and high SES families—the Early Childhood Longitudinal Study (ECLS) and the Norwegian Twin Registry. The ECLS will allow Turkheimer to examine six-month and two-year evaluations to see if heritability differences between SES groups are visible—even in such an early stage of development. Data pinpointing when differences in heritability emerge will help Turkheimer isolate environmental determinants of intelligence in low SES children.