Measured IQ differences between racial groups partly reflect innate cognitive differences.

In October 1994, a 845-page book landed on the desks of book reviewers, policy analysts, and school administrators across America with the force of something that felt, to many readers, like a scientific verdict. Charles Murray and Richard Herrnstein's The Bell Curve devoted several chapters to arguing that measured IQ differences between racial groups, particularly the roughly fifteen-point gap between Black and white Americans on standardized tests, reflected, at least in part, genuine genetic differences in cognitive ability. The book sold three hundred thousand copies in its first three months. Newsweek ran it as a cover story. Op-ed pages treated it as settled science requiring a policy response.

The history of that claim, however, was neither as new nor as settled as the book's reception suggested. The idea that racial groups differ in innate intelligence had been a staple of American and European academic literature since the late nineteenth century. Francis Galton, the Victorian statistician who coined the word eugenics, asserted in 1869 that African peoples sat near the bottom of a fixed intellectual hierarchy. The U.S. Army's mass intelligence testing during World War I, administered to nearly two million draftees by psychologist Robert Yerkes, produced data showing lower average scores for Black soldiers, which was promptly cited as confirmation of innate difference rather than as evidence of unequal schooling and living conditions. The tests themselves asked questions about tennis courts and the proper use of a carburetor, drawing on cultural knowledge systematically unavailable to men who had grown up under sharecropping or legally enforced segregation.

By 1994, the methodological landscape had changed substantially, but the critique of genetic interpretations had deepened too. Psychologist Claude Steele, working at Stanford, had by the mid-1990s developed a body of experimental work on what he called stereotype threat, the finding that members of groups associated with negative intellectual stereotypes perform measurably worse on cognitive tests when that stereotype is made salient. In controlled experiments, the same Black students who scored comparably to white students in one condition scored lower when told the test measured intelligence. The gap was not fixed; it moved in response to social context.

The American Psychological Association convened a task force within weeks of The Bell Curve's publication, assembling eleven psychologists to review the evidentiary record. Their report, "Intelligence: Knowns and Unknowns," was published in the journal American Psychologist in February 1996 under the chairmanship of Ulric Neisser of Emory University. On the question of genetic explanations for group differences in IQ scores, the task force's conclusion was direct: the evidence simply did not support it. The report found that socioeconomic variables explained a large portion of the gap, that test design reflected cultural content that disadvantaged some groups, and that the known environmental factors, nutrition, prenatal care, school quality, poverty, exposure to lead, were fully sufficient to account for observed differences without invoking genetics at all.

The task force also noted what was perhaps the most damning single data point against the hereditarian interpretation: the Flynn effect. Psychologist James Flynn had documented across multiple countries that raw IQ scores had been rising by roughly three points per decade throughout the twentieth century, gains far too rapid to reflect genetic change and attributable instead to environmental improvements such as better nutrition, reduced infectious disease, and expanded formal schooling. If environment could move population-average scores upward by fifteen points within a single generation, there was no logical basis for treating a fifteen-point gap between groups as evidence of anything genetic.