The Bell Curve

Herrnstein and Murray’s The Bell Curve (1994) is one of the most controversial and widely debated works of social science in the second half of the twentieth century. Almost instantly upon publication, the book set off a firestorm that took years to die down. What were the authors saying that was so incendiary? Their main arguments can be summarized approximately as follows. The US has increasingly evolved into a society stratified along the lines of intelligence. At the top of this stratification system is a cognitive elite of highly educated professionals, business managers, government officials, and the like who are increasingly set off from the rest of the population by their very high levels of intelligence. The cognitive elite has become increasingly separated from the rest of society by their attendance at elite universities, where they meet other highly intelligent individuals and intermarry, thus producing highly intelligent children who are likely to remain members of the elite intergenerationally. These consequences have resulted substantially from the fact that intelligence is highly genetically heritable, on the order of 40–80 percent. Intelligence is of great social importance. High intelligence is necessary for high levels of educational attainment, social status, and income. By contrast, low intelligence is associated with low levels of these outcomes, and also with a variety of social pathologies, such as higher rates of illegitimacy, poverty, welfare dependency, and crime. There are significant differences among racial and ethnic groups in intelligence, and these differences are largely genetic in origin. Such differences go far in explaining why blacks are overrepresented in the  categories of social pathology mentioned  above. The  situation seems to be worsening, and thus the gap between the cognitive elite and the underclass growing, because of the tendency of poorer individuals of lower intelligence to out reproduce the more wealthy and more highly intelligent. Moreover, ‘‘Unchecked, these trends will lead the US toward something resembling a caste system, with the underclass mired ever more firmly at the bottom and the cognitive elite ever more firmly anchored at the top’’ (p. 509).

Although The Bell Curve is not primarily about race, most of the controversy focused on the chapters that claimed that racial and ethnic differences in IQ scores have a large genetic component. Data presented by the authors show that the group that scores the highest on IQ tests is Jews, especially Ashkenazi Jews of Eastern European origin, and almost all American Jews are so descended. The authors report that Ashkenazi Jews score, on average, about a half to a full standard deviation above the mean for whites, which translates into roughly 7–15 IQ points. Next in line are East Asians and Americans of East Asian descent, who tend to score an overall average of about 106 (with about 110 on the spatial mathematical component and 97 on the verbal component). American whites and Western European whites average about 100. American blacks average about 85, or a full standard deviation below whites. Actually, Herrnstein and Murray compile the results from 156 studies to show that the average black–white difference is 1.08 standard deviations, or about 16 IQ points.

Although a standard objection to IQ tests is that they are culturally biased, the authors show that on those test items deemed the most culturally biased, blacks actually score higher than on the so called culturally neutral items. The other major standard objection to such findings is that IQ is highly correlated with social environment, especially socioeconomic level. Indeed, this is so, and both whites and blacks of higher socioeconomic status have higher reported IQ scores. However, the black–white gap does not diminish when socioeconomic status is controlled. Indeed, it widens.

Herrnstein and Murray show that cognitive test scores are excellent predictors of economic success, and, moreover, that the gap in earnings between American whites and blacks virtually disappears when cognitive test scores are controlled. When these scores are factored out of the equation, black income is 98 percent of white income. This finding leads the authors to conclude that the black–white income gap has very little to do with racism or racial discrimination and mostly to do with differences in cognitive abilities.

In the years immediately following the publication of The Bell Curve there appeared a ‘‘mountain of essays and books purporting to refute that work and its conclusions’’ (Chabris 1998). As of 1998 at least five major critical books had appeared. Two of these are works by serious social scientists: Devlin et al. (1997) and Fischer et al. (1996). Devlin et al. (1997) contend that the heritability of IQ is much lower than the .40–.80 claimed by Herrnstein and Murray. They also point to adoption studies that they claim show that IQ is largely determined by environment. Fischer et al.

(1996) contend that intelligence is a poor explanation of social inequalities because the abilities of individuals are much more complex and changeable than can be captured by old fashioned notions of intelligence. Social inequalities, they claim, are determined more by patterns of education, jobs, and taxation. As for race differences, they claim that ethnic minorities  score low on  intelligence tests because they are of low status, not that they are of low status because they score low on intelligence tests.

In defense of The Bell Curve, Bouchard (1995) claimed that, in fact, the evidence shows that low IQ is an important risk factor for poor social and economic outcomes and that high IQ is an important protective factor. The effect of IQ is much greater than parental socioeconomic status. Moreover, because of the enormous controversy the book engendered, the American Psychological Association created a task force on intelligence, which gave its report in 1996 (Nessieret al. 1996). The task force concluded that the size of the black–white IQ difference is indeed approximately one standard deviation; that cultural biases in IQ tests cannot explain this difference; and that IQ tests are equally predictive of social, economic, and educational outcomes for both blacks and whites (cf. Murray, 2005).

In terms of policy recommendations, Herrnstein and Murray oppose Affirmative Action and other compensatory programs on the grounds that they either have not worked, or have actually worsened the situation for minorities. The authors favor a society in which everyone has a valued place commensurate with their abilities. They do not favor wholesale income redistribution, but they do favor augmenting the incomes of the poorest segments of the population so that an income floor is established. They also favor policies that would strengthen marriage, since single parenting is a serious risk factor for low social outcomes.


  1. Bouchard, J. Jr. (1995) Breaking the Last Taboo. Contemporary Psychology 40.
  2. Chabris, F. (1998) IQ Since ‘‘The Bell Curve.’’ Commentary 106(2): 33-40.
  3. Devlin, B., Fienberg, S. E., Resnick, P., & Roeder, K. (Eds.) (1997) Intelligence, Genes, and Success: Scientists Respond to The Bell Curve. Springer, New York.
  4. Fischer, S., Hout, M., Jankowski, M. S., Lucas, S. R., Swidler, A., & Voss, K. (1996) Inequality by Design: Cracking the Bell Curve Myth. Princeton University Press, Princeton.
  5. Herrnstein, R. J. & Murray, C. (1994) The Bell Curve: Intelligence and Class Structure in American Free Press, New York.
  6. Murray,   (2005)  The  Inequality  Taboo. Commentary 120(2): 13 22.
  7. Nessier, et al. (1996) Intelligence: Knowns and Unknowns. American Psychologist 51: 77-101.

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