IQ Test Scores

Cultural Differences in IQ Test Scores

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Most studies carried out in the United States to measure intelligence (IQ) indicate a significant gap in the IQ test scores of Blacks and Whites. The gap is more pronounced in certain areas of intelligence such as general intelligence and on tests requiring problem solving and more complex mental operations than on tests of rote learning and immediate memory. The gap has narrowed since the 1970s but still persists stubbornly. Debate has raged among the psychologists and social scientists about the reasons for the gap. The “hereditists” believe that the difference in the IQ test scores of Blacks and Whites is largely due to genetic reasons. The “environmentalists” are equally certain that the gap is due to environmental reasons and has nothing to do with genetics. This paper looks at both the heredity explanation as well as the environmental explanations of the gap in the IQ scores. It shall also examine whether the difference in the IQ scores can be explained by “Cultural bias” in the IQ tests.

Heredity Explanation & “The Bell Curve”

The genetic explanation for the IQ difference between different races has a long history and the “Whites” have not always been held to possess superior intelligence. For example, when the Moors from North Africa invaded Europe in the 8th century AD, they speculated that the Europeans might be congenitally incapable of abstract thought. (Nisbett 1998, p 86) When the U.S. Army started a large-scale mental testing program in 1917 for testing the intelligence of its recruits, it found that whites scored substantially higher than blacks. Social Darwinists and Biological Determinists jumped on the finding, citing it as evidence that whites had “more innate ability than blacks.” (Jencks and Philips, 1998, p.16) In the post-World War II backlash against the genetic differences among human beings, such explanations were discredited and remained suppressed until the 1960s. The genetic-IQ debate was revived in the U.S. after the appearance of a famous Harvard Educational Review article by Arthur Jensen in 1969. Jensen’s thesis in the article was that most of the variation in the IQ test scores of blacks and whites is due to innate genetic reasons since a plausible environmental explanation for the black-white gap has not been forthcoming.

The Bell Curve Controversy

Another controversial book The Bell Curve: Intelligence and Class Structure in American Life appeared in 1994 written by the late Richard J. Herrnstein and Charles Murray. The book received enormous public attention and media coverage due to its contentious argument that innate genetic factors, not just have a significant effect on IQ scores at the individual level, but are also important at the group level. The other major thesis of the book is that the IQ rather than most of the social behaviors of the people. The book was pilloried by the liberal critics who accused the authors of reviving the of eugenics. Most right wing and some conservative intellectuals, on the other hand, defended the findings of the Bell Curve as serious scientific work based on extensive research and “indisputable evidence.”

In the presence of such divergent views on the “hereditary explanation” of the IQ gap, is it possible to ‘sift wheat from the chaff?’ In order to try and do so, let us look at the evidence presented by the authors of the Bell Curve and other proponents of the hereditary explanation of differences in IQ of different racial groups. Various studies have been performed to determine the relevance of group heredity on the IQ difference between blacks and whites. Studies that assess heritability by correlating the IQ scores of African-Americans with the percentage of their genes that are “European” are most relevant for this purpose. If blacks with more European genes were demonstrated to have higher IQ scores, there would be some grounds for the genetic hypothesis. (Nisbett 1998) On the other hand, if no such co-relation is found the genetic hypothesis is greatly discredited. Nisbett asserts that none of the as well as blood sampling carried out so far give any (or at best very weak) co-relation between percentage of European ancestry and IQ score. For example, in studies carried out by Sandra Scarr on the basis of blood groups, the correlation between IQ and European heritage was only 0.05 in a sample of 144 pairs of black adolescent twins. Typical correlations with skin color are around 0.15. Since blood testing is a more accurate indicator of European ancestry (lighter skin color may be due to other factors too), the negligible co-relation found between greater European ancestry and higher IQ scores is particularly damning for the hereditary explanation of the IQ gap. (Ibid. p 90)

What then are the reasons behind such wide acceptance of the Bell Curve and the hereditary explanation? One reason of course is the very real gap between the IQ scores of the black and white population in the United States, which some people feel is far too much to be explained by environmental reasons alone. The other reason could be the presence of a sizable population of “closet racists” in the U.S., who have been provided with a supposed ‘scientific’ basis by the Bell Curve for believing in the intellectual inferiority of the blacks. Hence, despite the fact that the findings of the Bell Curve were never published in peer-reviewed journals, a number of right-leaning critics and readers have enthusiastically accepted the purported scientific credentials of the book. (Dorfman 1995).

Another recent philosophical work that supports the essentialist argument of intelligence being inherently linked to race is Michael Levin’s Why Race Matters (1997). Levin argues that persons of the European and the so-called ‘Caucasoid’ races are more intelligent than persons of the black African race mainly because of the more challenging colder climate of Europe which led to a more cognitively evolved branch of Homo sapiens in Europe. This argument does not stand up to scientific scrutiny since the Neanderthal man existed in Europe for more than 300,000 years but was less cognitively evolved than the Homo sapien Africanus who migrated to Europe from Africa. (Keita 1999). Levin’s basic argument about the lower IQ scores of the black race is also not supported by facts: the IQ scores of Southern Europeans, West Asians, South Asians, and Eskimos are similar to those of persons of African descent. (Ibid.)

Environmental Explanation for the IQ Gap

The environmental explanation for the IQ gap between people of African and European descent is in a way exactly opposite of the “hereditary” explanation and the Bell Curve theory. While hereditists contend that IQ largely determines most socio-economic behaviors, environmentalists believe that IQ is mainly determined by the socio-economic factors. The key question again is: how far is the environmental explanation supported by the studies carried out so far? Two very important studies in this regard were a) A study that compares the IQs of German children fathered by black American GIs during the occupation of Germany after WWII and the IQs of children fathered by white GIs; and b) studies that compared the IQ scores of mixed-race children (children having black mothers and black fathers). The results of both studies strongly suggest that environmental rather than genetic factors determine IQ. For instance, in the study of children fathered by black and white GIs in Germany, no significant difference in IQs of the two groups of children was found (children with black fathers had an average IQ score of 96.5 and those fathered by white GIs had an average IQ of 97). In the second study, children of white mothers and black fathers were found to have a 9-point IQ advantage over children with black mothers and white fathers. (Nisbett 1998, p. 92) Since mothers are more important to the intellectual socialization of their children than fathers, the higher IQ scores of mixed-race children with white mothers strongly support the view that ‘environmental’ influence is almost exclusively responsible for the IQ scores. Hence, even if the mother’s socialization influence is assumed to be the sole environmental influence on their children’s IQ scores, the 9-point difference in IQs can be assumed as the environmental contribution. This alone accounts for the current 10-point difference in the IQs of black and white Americans. (Ibid.)

Income & Minority Groups. Incomes of Black Americans and minority groups in the United States, although still lagging behind the European-Americans, have improved since the sixties. This is reflected in two studies carried out in the 1960s and 1990s. A 1964 study shows that employed black men on average earned 57.5% of white male earnings and blacks with Armed Forces Qualification Test (AFQT) scores above the national average, earned 64.5% of what whites earned. A similar study conducted in 1993, showed that blacks’ average earning was 67.5% whites’ average earnings, but blacks with AQT scores above the national average, earned 96% of the white average. (Jencks and Philips, 1998, p. 4) This seems to indicate a strong co-relation between IQ scores and incomes but it must be remembered that blacks having high IQ scores are also better educated and may come from higher income families and better social backgrounds, so it is hard to quantify the exact co-relation between IQ and test scores.

Income & Education. A review of the SAT scores of a single year (2001) indicates that there is a strong co-relation between the family income and the SAT scores. For example, the total (Math + Verbal) SAT score of all test takers with family income below $10,000/year (the lowest category) is 864. The test score rises in close relation to family income and is the highest (1126) for the test takers in the highest income bracket of $100,000/year. (Houghton 2002)

SAT scores by Ethnic groups for the same year (2001) indicate that African-Americans have the lowest total score (859), while the whites have a total score of 1060. Asian-Americans have the highest total (1067) among ethnic groups. (Ibid.) The test scores of the ethnic groups strongly co-relate with the incomes of the ethnic groups since the median income for 1999 of Asian-Americans ($51,205) compares with $44,316 for whites and $27,910 for blacks. (Ibid) It may be noted that co-relation of family incomes with test scores is indicative of the socio-economic condition or the environmental effect on IQ; it is not the same as the effect of IQ on incomes that Bell Curves propagates.

Cultural Bias of IQ Tests

IQ tests in the U.S. have always been accused of a pronounced “Cultural bias” against the minority groups. Christopher Jencks in his research has identified five possible varieties of racial bias in testing and concluded that two of the five constitute serious problems, while the remaining three are of minor importance. (Jencks and Phillips 1998, p. 12)

The “content bias” and the “selection system bias” have been identified as more serious. ‘Content bias’ in tests refer to their tendency to draw upon language, terms, expressions, and values familiar to white, middle-class America, but relatively unfamiliar to black and other minority cultural groups such as the Hispanics. An appropriate example is the use of analogies, whose content, values or meanings embedded in a socio-cultural context that is more familiar to one group but may be unfamiliar to another. As a result, test scores may not always reflect actual ability of test takers. The “selection” bias crops up when selections for employment and admission are based solely on the basis of test scores. This is because the blacks perform much better on the non-cognitive determinants of job or academic performance than on the cognitive ones; hence a selection system based on test scores for employment or admission invariably works against the blacks and other cultural minority groups who traditionally score low on such tests. (Ibid, p. 15)

Other cultural bias that Jencks has identified but considered less important are termed “labeling bias,” “prediction bias” and “methodological bias.” Labeling bias arises when a test claims to measure one thing but really measures something else, e.g., tests labeled as “intelligence” or “aptitude” tests that purport to test innate ability while such abilities are in reality, at least partially “developed” traits. “Prediction bias” refers to the inaccurate prediction of future performance by a test, while “Methodological bias” is the assessment of information in a way that underestimates the competence of one group relative to another. (Ibid pp 12-16)


The gap in the IQ test scores of African-Americans and European-Americans has aroused heated debate ever since it was discovered in the early part of the twentieth century. Various theories have been forwarded by social scientists for the phenomenon that can be broadly classified as “hereditary” and “environmental.” Most studies and scientific observation point to a strong co-relation between the environment and IQ score rather than being an innate racial trait. As we saw in this essay, a certain amount of cultural bias in tests may also be responsible for the IQ gap between various racial groups.


Dorfman, Donald D. (1995). “Soft Science with a Neoconservative Agenda.” A Review of the Bell Curves. 40: 5. Contemporary Psychology, APA’s journal of book reviews. Retrieved on June 20, 2004 at

Haughton, Noela A. (2002). “Biased Content, Context, and Values: An Examination of the SAT.” Retrieved on June 20, 2004 at

Jencks, Christopher and Phillips, Meredith. (1998). “The Black- White Test Score Ga: An Introduction.” (pp. 2-22) The Black-White Test Score Gap. Christopher Jencks and Meredith Phillips – eds. Washington, DC: Brookings Institution Press.

Keita, L. (1999). “Why Race Matters: Race Differences and What They Mean.” The Western Journal of Black Studies. 23: 1, p. 65.

Nisbett, Richard E. (1998). “Race, Genetics, and IQ.” (pp. 89-102). “The Black- White Test Score Ga: An Introduction.” The Black-White Test Score Gap. Christopher Jencks and Meredith Phillips – eds. Washington, DC: Brookings Institution Press.

Often termed simply as “g”

The average IQ scores of blacks was one standard deviation below that of whites until the 1970s. Recent studies indicate that it has narrowed down to about

The hereditary vs. environmental debate has heated up ever since the publication of the popular book The Bell Curve: Intelligence and Class Structure in American Life by Richard Herrnstein and Charles Murray in 1994

The Nazi’s were of course the most notorious proponents of the theory of inherent intelligence and believed that the Jews, Blacks and the Gypsies were “feeble minded” and only the White Aryan race had the capability of making positive contribution to the human civilization.

Herrnstein was a professor of psychology at Harvard who died just before the publication of The Bell Curve

The critics of the Bell Curve were particularly incensed at the inferences drawn by the authors from selected research that call for cutting welfare spending and putting severe restriction on immigration since “Latino and black immigrants are…putting some downward pressure on the distribution of intelligence.”

Such a correlation could be due to environmental reasons since blacks with lighter skins and more ‘Caucasian features’ could have social and economic advantages in the American society that would lead to higher IQs

When skin color and socio-economic factors are controlled, this co-relation drops to minus 0.02

The West and South Asians are classified as ‘Caucasoid’ while the Eskimos are ‘Mongoloids’ who are supposed to have similar IQs as the white. The Southern Europeans are of course white

IQ Scores