Schools, skills, and synapses

Economic Inquiry, July, 2008 by James J. Heckman

For example, recent work by Caspi, Williams, Kim-Cohen et al. (2007) shows that children's intellectual development is influenced by both genetic and environmental factors. Breast-fed children attain higher IQ scores than non-breast fed children. This relationship is moderated by a gene (FADS2) that controls fatty acid pathways. Fraga, Ballestar, Paz et al. (2005) show how monozygotic (identical) twins are affected by life experience that substantially differentiates the genetic expression of adult twins. (13) Caspi, Sugden, Moffitt et al. (2003) show that one gene (a serotonin transporter 5-HTT) moderates the influence of stressful life events on depression. Caspi, McClay, Moffitt et al. (2002) show that the impact of growing up in a harsh or abusive environment on adult antisocial behavior depends on the absence of a particular variant of the MAOA gene. Cole, Hawkley, Arevalo et al. (2007) show the effect of social environments (isolation) on gene expression that moderates adverse health outcomes. Turkheimer, Haley, Waldron et al. (2003) find a powerful role of environment in determining heritability of IQ.

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Research on animals by Champagne and Curley (2005) and Champagne, Weaver, Diorio et al. (2006) shows that environmental effects are inherited across generations, and that early environmental influences are especially important. Suomi (1999, 2003) reports parallel findings on genetic moderation of environmental influences for rhesus monkeys that have 95 percent of human genes.

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When one controls for early family background factors (mother's education and ability) using regression analysis, the gaps shown in Figures 11(a) and 12(a) greatly diminish. See Figures 11(b) and 12(b), respectively. While such regression adjustments cannot establish causality, a causal interpretation of this evidence is supported by the experimental evidence discussed in Section VII.

V. THE DECLINE OF THE AMERICAN FAMILY AND THE RISE OF SOCIAL PROBLEMS

The evidence on the importance of family factors in explaining ability gaps is a source of concern because a greater proportion of American children is being born into disadvantaged families. A divide is opening up in American society. Those born into disadvantaged environments are receiving relatively less stimulation and fewer resources to promote child development than those born into more advantaged families. Figure 13(a) shows the dramatic rise in the proportion of children living in single parent families. The greatest contributor to this growth is the percent living in families with never married mothers. (See the top category.) Such families are much less likely to invest in their children (Moon, 2008). Figure 13(b) shows that the percentage of all children less than age 5 with a never married mother is over 25% for children born into families with dropout mothers. Figure 13(c) shows that this phenomenon is especially pronounced for African-American families.

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A gap has emerged between the environments of children of more educated women and the environments of children of less educated women. More educated women are having their children later after they have completed their education and have a steady flow of resources from their own income and that of their spouses (McLanahan, 2004).