IQ since The Bell Curve

Christopher F. Chabris, Commentary, August 1998.


In The Bell Curve, Herrnstein and Murray set out to prove that American society was becoming increasingly meritocratic, in the sense that wealth and other positive social outcomes were being distributed more and more according to people’s intelligence and less and less according to their social backgrounds. Furthermore, to the extent that intelligence was not subject to easy environmental control, but was instead difficult to modify and even in part inherited, genetic differences among individuals, Herrnstein and Murray posited, would contribute significantly to their futures.

The evidence for this thesis came largely from an analysis of data compiled in the National Longitudinal Study of Youth (NLSY), an ongoing federal project that tested over 10,000 Americans in 1980, with follow-up interviews regularly thereafter. Each participant completed the Armed Forces Qualifying Test (AFQT)–which, like any diverse test of mental ability, can be used as a measure of intelligence–and was then evaluated for subsequent social outcomes (including high-school graduation, level of income, likelihood of being in jail, likelihood of getting divorced, and so forth). As a rule, a person’s intelligence turned out to predict such outcomes more strongly than did the socio economic status of his parents. This relationship held for all ethnic groups; indeed, when intelligence was statistically controlled, many “outcome” differences among ethnic groups vanished.

Herrnstein, a professor of psychology at Harvard with an impeccable reputation for scientific integrity, died of cancer just a week before The Bell Curve arrived in bookstores. This in itself may have had something to do with the frenzy of the public response. Had Herrnstein lived to participate in the debate, critics might have found the book harder to malign than it became when Murray, whose training was not in psychology but in sociology, was left to promote and defend it by himself.

Not that Murray, the author of Losing Ground (1984) and a vocal critic of the liberal welfare state, failed to do so energetically. But his lack of credentials as a hard scientist, and his overabundant credentials as a scourge of liberalism, made him a tempting target for an attack that was itself motivated as much by political as by scientific differences, and that was almost entirely focused on a side-issue in the book. That side-issue was differences in intelligence not among individuals but among groups–and specifically between whites and blacks–the degree to which those differences might or might not be explained genetically. So heated, and so partisan, was the furor at its peak that even President Clinton was asked about the book at a press conference. (He had not read it, but disagreed with it nonetheless.)