A statistical analysis of four national intelligence tests indicates that the difference in scores between blacks and whites decreased by about a third between 1972 and 2002. The findings challenge a century-old argument that the racial gap in performance on IQ tests is primarily genetic and therefore invulnerable to social change, say the researchers who performed the new study.
In the new analysis, all four tests reflected a similar gap in 1972 but indicated that blacks have since gained ground in IQ.
“The whole distribution of black cognitive ability is moving up relative to whites,” says Dickens. “There’s no reason to believe [the gap] isn’t going to get more narrow as we move forward and as measures of social equality continue to improve.”
Neither increased rates of mixed ancestry nor changes in test content explain the narrowing gap, Dickens and Flynn argue in the October Psychological Science.
Last year, a review by J. Philippe Rushton of the University of Western Ontario in Canada and Arthur Jensen of the University of California, Berkeley concluded that intelligence is determined predominantly by genetics. The researchers argued that the IQ gap had held steady for a century, despite social-equality efforts, and noted that studies of adopted children and twins have attributed 80 percent of the gap to genetics.
The new data, by contrast, instead indicate that environmental factors contribute greatly to IQ scores, says Flynn. “It’s exciting to show that the gap isn’t written in the stars,” he says.
But the new findings contain many holes, Rushton and Jensen maintain in a rebuttal published with the study. For example, Dickens and Flynn “cherry-picked” their results by leaving out four tests that don’t support their conclusions, Rushton says.
Dickens answers that the tests that he and Flynn omitted were less reliable than the ones that they included.
A 4-to-7-point closure in the gap would be “truly astounding,” says Linda Gottfredson of the Delaware—Johns Hopkins Project for the Study of Intelligence and Society.
However, the conclusion “just doesn’t fit” with data showing that in the past 30 years, U.S. black children between the ages of 9 and 17 have approached white children in reading scores but not in science and math, she says. If general intelligence, as measured by IQ tests, were really rising, scores would have increased in all subjects.
The new findings “won’t change that many minds,” says Doug Detterman of Case Western Reserve University in Cleveland, who is editor of the journal Intelligence. More important than measuring a gap, he says, is identifying the specific environmental factors or genes that contribute to intelligence.