Human races are distinct biological categories with innate differences in intelligence and ability.

In the mid-nineteenth century, physicians, anthropologists, and naturalists in Europe and North America developed what they claimed was a scientific taxonomy of humanity. Samuel Morton's collection of more than 800 human crania, catalogued in the 1840s, was presented as empirical evidence that brain sizes placed different races in a natural hierarchy. Paul Broca in France and Francis Galton in Britain extended similar methods through the latter half of the century. By 1900, the idea that humanity was divided into discrete biological races with inherent cognitive differences had achieved the status of academic consensus in Western science. It was embedded in law, taught in universities, and cited in courtrooms.

The framework was never as stable as its proponents believed. Depending on the author, the number of human races varied from three to more than thirty. The physical traits used to define them — skin color, hair texture, skull dimensions — did not sort into the same groups when analyzed separately. Populations shaded continuously into one another at geographic boundaries rather than forming discrete clusters. These inconsistencies were noted and dismissed as problems of measurement rather than problems with the underlying concept.

The collapse began in earnest after World War II, when the uses to which racial science had been put became impossible to separate from its methods. The UNESCO Statement on Race, issued in 1950 and revised in 1951 with additional signatures from geneticists, declared that there was no scientific basis for assuming that human groups differed in innate mental characteristics. The pivotal analytical work came from population genetics. Richard Lewontin's 1972 analysis of variation in blood group alleles found that approximately 85 percent of all human genetic variation occurs within conventionally defined racial groups rather than between them — a proportion too small to sustain a biologically meaningful taxonomy. Subsequent genomic analyses have consistently replicated this finding. Human populations show geographic patterns of genetic variation, the product of migration history and local adaptation, but these patterns form gradients rather than discontinuous categories.

The hereditarian claim did not disappear from public discourse. In October 1994, a 845-page book landed on reviewers' desks with the force of something that felt like a scientific verdict. Charles Murray and Richard Herrnstein's The Bell Curve devoted several chapters to arguing that 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 raising legitimate scientific questions requiring a policy response.

The history of that specific claim was neither as new nor as settled as the book's reception suggested. The U.S. Army's mass intelligence testing during World War I, administered to nearly two million draftees, had produced data showing lower average scores for Black soldiers — data promptly cited as confirmation of innate difference rather than as evidence of unequal schooling and living conditions under legally enforced segregation. The tests themselves asked questions about tennis courts and carburetor operation, drawing on cultural knowledge systematically unavailable to men who had grown up under sharecropping.

By 1994, the methodological critique had deepened substantially. Psychologist Claude Steele, working at Stanford, had developed a body of experimental work on 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," published in American Psychologist in February 1996, was direct: the evidence did not support genetic explanations for group differences in IQ scores. Socioeconomic variables explained a large portion of the gap; test design reflected cultural content that disadvantaged some groups; and known environmental factors — nutrition, prenatal care, school quality, poverty, exposure to lead — were fully sufficient to account for observed differences without invoking genetics.

The task force also noted 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, attributable instead to environmental improvements such as better nutrition, reduced infectious disease, and expanded 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.