Tuesday, September 02, 2003

The Interaction of Class and Genes in Determinining IQ Heritability

This report in the Washington Post strikes me as being mere common sense. Why anyone would expect anything different is beyond me. Isn't it obvious that the less held back one is by the circumstances of one's birth, the greater the role one's own inherited qualities will play in one's achievements?

Genes' Sway Over IQ May Vary With Class
Study: Poor More Affected by Environment

By Rick Weiss
Washington Post Staff Writer
Tuesday, September 2, 2003; Page A01

Back-to-school pop quiz: Why do poor children, and especially black poor children, score lower on average than their middle-class and white counterparts on IQ tests and other measures of cognitive performance?

It is an old and politically sensitive question, and one that has long fueled claims of racism. As highlighted in the controversial 1994 book "The Bell Curve," studies have repeatedly found that people's genes -- and not their environment -- explain most of the differences in IQ among individuals. That has led a few scholars to advance the hotly disputed notion that minorities' lower scores are evidence of genetic inferiority.

Now a groundbreaking study of the interaction among genes, environment and IQ finds that the influence of genes on intelligence is dependent on class. Genes do explain the vast majority of IQ differences among children in wealthier families, the new work shows. But environmental factors -- not genetic deficits -- explain IQ differences among poor minorities.

The results suggest that early childhood assistance programs such as Head Start can help the poor and are worthy of public support. They also suggest that middle-class and wealthy parents need not feel guilty if they don't purchase the latest Lamaze mobile or other expensive gadgets that are pitched as being so important to their children's development.

"How many books are in the home and how good the teacher is may be questions to consider for a middle-class child, but those questions are much more important when we're talking about children raised in abject poverty," said lead researcher Eric Turkheimer, a psychologist at the University of Virginia.

The work, to be published in the November issue of the journal Psychological Science, is part of a new wave of research that embraces a more dynamic view of the relationship between genes and environment. Although older research treated nature and nurture as largely independent and additive factors, and saw people as the sum of their genetic endowments and environmental experiences, the emerging view allows that genes can influence the impact of experiences and experiences can influence the "expression," or activity levels, of genes.

In Turkheimer's study, the impact of genes on IQ varied depending on a child's socioeconomic status (SES), a sociological measure that includes household income and other elements of class and social status.

Until recently, Turkheimer and others said, research had indicated that the "heritability" of IQ -- that is, the degree to which genes can explain the differences in IQ scores -- completely dominated environmental influences. That led some to call into question the value of programs such as Head Start, which are based on the assumption that by improving the childhood environment through extra attention, nutrition and care, a child's intellectual future could be improved.

But it turned out that virtually all those studies on the heritability of IQ had been done on middle-class and wealthy families. Only when Turkheimer tested that assumption in a population of poor and mostly black children did it become clear that, in fact, the influence of genes on IQ was significantly lower in conditions of poverty, where environmental deficits overwhelm genetic potential.

"This paper shows how relevant social class is" to children's ability to reach their genetic potential, said Sandra Scarr, a professor emerita of psychology now living in Hawaii, who did seminal work in behavioral genetics at the University of Virginia.

Specifically, the heritability of IQ at the low end of the wealth spectrum was just 0.10 on a scale of zero to one, while it was 0.72 for families of high socioeconomic status. Conversely, the importance of environmental influences on IQ was four times stronger in the poorest families than in the higher status families.

Given the pleasure many people seem to obtain in attributing black performance on IQ tests to supposedly "genetic" influences, it will be interesting to see whether the existence of this report is even acknowledged in certain quarters, much less factored into the claims these parties will make in the future. When we consider how low the heritability estimate is for black Americans growing up in what are, by Third World standards, luxurious conditions, are we not justified in suspecting that the heritability measure in the African context would be essentially zero?