Myth: The black/white IQ gap is largely genetically caused.

Fact: Almost all studies show the black/white IQ gap is environmental.


Since the publishing of The Bell Curve, a definitive study has come out of Columbia and Northwestern Universities demolishing the theory that the white/black IQ gap is largely genetically caused. But even at the time The Bell Curve was published, there was no reason to make such a claim. Of the seven major scientific studies on genes, race and IQ, six suggested that genes play no role in the IQ gap between whites and blacks, and only one suggested a genetic cause. Statistical objections can be raised to all seven early studies, but at the very least, The Bell Curve had no grounds whatsoever to imply that the IQ gap is largely genetic.


In The Bell Curve, authors Herrnstein and Murray strongly implied that the white/black IQ gap is largely genetic. (They were careful not to state that claim explicitly.) A year and a half after the book came out, scientists released the results of a well-designed, long-term study that appears to have refuted this contention. Their press release is worth quoting in full:

The Bell Curve's one-sided analysis

At the time of The Bell Curve's publishing, there were seven studies in the scientific literature concerning the cause of the black/white IQ gap. Six of them point to the environment; and only one points to genetics. The authors of The Bell Curve prominently displayed only the results of the pro-genetics test in the main text. Of the others, they dismissed one in a single-paragraph side bar, dismissed another in the endnotes, and simply ignored the rest.

Psychologist Richard Nisbett has been generous enough to provide the public with the details of all seven studies: (2)

After World War II, many American GI's (both white and black) fathered children by German women; these children were then raised in German society. The children fathered by black GI's had an average IQ of 96.5, and the children fathered by white GI's had an average IQ of 97 -- a statistically insignificant difference. (3)

In another study of children raised in residential institutions, black, white and racially mixed children who were raised in the same enriched environment were given IQ tests. At four years of age, the white children had an average IQ of 103, the blacks had an average IQ of 108, and the racially mixed children had an average IQ of 106. (4)

Another study measured the IQ's of children from black-white unions. Assuming that mothers are more important than fathers in the education and socialization of their children, the study sought to see if a child's IQ is higher when the white partner is the mother. This turned out to be true -- the IQ of a racially mixed child averages 9 points higher when it is the mother who is white. (5)

A genetic study took advantage of the fact that African-Americans genes are about 20-30 percent European, and that Africans and Europeans differ just enough in their genetic blood groups to determine the degree of "Europeanness" in an individual. If intelligence were indeed genetic and favored in Europeans, we might expect blacks with greater Europeanness to be more intelligent. However, a study of 288 young blacks found almost no relationship between Europeanness and intelligence: the correlation was a trivial and nonsignificant .05. (6)

Another genetic study examined the correlation between IQ and European blood groups (as opposed to the estimated Europeanness of individuals based on blood groups). In one sample of blacks, the correlation was a trivial .01, in the other a nonsignificant -.38, with higher IQ being associated with the more African blood groups. (7)

Another study tested the hypothesis that if IQ were both hereditary and favored in Europeans, then blacks with high IQs should have several times the level of Europeanness than the black population in general. But a study of high-IQ black children in Chicago found that this wasn't the case; in fact, these black children were slightly less likely to have European ancestors. (8)

The study featured in The Bell Curve was the Scarr-Weinberg study, which examined the IQs of children from different races who were adopted by white parents. White adoptees turned out to have higher IQs than mixed-race adoptees, who had higher IQs than black adoptees. (9)

There are statistical difficulties with all the above studies. For example, Scarr and Weinberg themselves believe that their adoption study is not informative on the question of genes, race and IQ, because their study sample was small, the adoption agencies could have selectively placed the kids, the adoptive families were recruited on a voluntary basis, the natural parents' IQs were not known, the black children were adopted at a substantially later age, and the social stigma of being a black child in a white family probably has effects on development. Curiously, The Bell Curve does not report the reservations that the study authors themselves have.

Many of the same objections can be raised to the other studies. The IQs of the parents were not known, and there is a possibility that the study samples were nonrepresentative of the population being studied. Possibly, whites who breed with blacks may tend to have lower IQs. (This assertion would beg support, however, since the biracial population in the U.S. first burgeoned during the days of slavery, when wealthy slave masters and plantation owners raped hundreds of thousands of black slaves.) However, as Nisbett points out, the six studies suggesting a social rather than genetic factor were taken at very different times and places, under a wide variety of circumstances. That they should all suffer from the same sort of self-selection is therefore implausibly great.

But even accepting the statistical difficulties of all seven studies, the authors of The Bell Curve were wrong to imply that the difference in black and white IQ scores is largely genetic. At the very least, they had no hard scientific evidence at the time; at the very most, the fact that the environmental results outnumbered the genetic results six-to-one makes their suggestion completely indefensible.

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1. Press Release from Columbia and Northwestern Universities, April, 1996. Contact: Pat Tremmel at (847) 491-4892 or or Barry Rosen at (212) 678-3176 or .

2. Condensed from Richard Nisbett's article "Race, IQ and Scientism," pp. 37-42 in Steven Fraser, ed., The Bell Curve Wars (New York: HarperCollins, 1995).

3. J.R. Flynn, Race, IQ and Jensen, (London: Routledge and Kegan Paul, 1980), pp. 87-88.

4. Ibid., pp. 110-111.

5. L. Willerman, A.F. Naylor and N.C. Myrianthopoulos, "Intellectual development of children from interracial matings: performance in infancy and at 4 years," Behavior Genetics 4, 1974, pp. 84-88.

6. S. Scarr, S. Pakstis, H. Katz and W. Barker, "Absence of a relationship between degree of white ancestry and intellectual skills within a black population," Human Genetics 39, 1977, pp. 73-77, 82-83.

7. J. Loehlin, S. Vandenberg and R. Osborne, "Blood-group genes and Negro-white ability differences," Behavior Genetics 3, 1973, pp. 263-70.

8. P. Witty and M. Jenkins, "The educational achievement of a group of gifted Negro children," Journal of Educational Psychology 25, 1934, p. 586. Levels of Europeanness in subjects were based on self-reports on their ancestries.

9. S. Scarr and R. Weinberg, "The Minnesota adoption studies: Genetic differences and malleability," Child Development 54, 1983, pp. 260-267.