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One of the most controversial issues in the relationship of heredity to intelligence concerns the issue of race. African Americans tend to score an average of 15 points lower on IQ tests than do Whites (Bracken & colleagues, 1993). Although other minorities in the United States, including Mexican Americans and Native Americans, also sometimes score lower on standardized tests, one exception is the mathematical skills of Asian Americans (D'Ailly, 1992). While there have been many explanations for these findings, Arthur Jensen (1969) caused a controversy in the academic community by suggesting that intelligence was due nearly exclusively (80 percent) to hereditary factors. And more recently, the genetic theory of racial differences in intelligence was supported by Herrnstein and Murray (1994), but again, not without controversy. Let's take a look at the facts to try to understand what conclusions might be reached concerning race and intelligence.
As reported in the text, the correlation for IQs of identical twins reared together is .86, suggesting that heredity largely accounts for the similarity. There are other possible interpretations of the data. For example, the .86 correlation for identical twins reared together is actually determined by both genetic and environmental factors. These twins not only share identical genes, but they also share nearly identical environments. It could be argued that environment is contributing much more than the .14 figure first suggested by the data. Keep in mind also that these correlations are for group data, and tell us nothing about individual scores. Indeed, there is more variation within a particular race than between two races. Thus, we cannot make a prediction about an individual from this group data. Since, until fairly recently, most intelligence tests were standardized for White, middle-class people, it is no wonder that other races do not score as well as Whites. Indeed, it could be argued that the earlier versions of intelligence tests were invalid for measuring intelligence of African Americans (Houston, 1990). The intelligence tests themselves could be biased. A number of attempts to construct a truly culture-fair intelligence test have shown only moderate success, and we are left with less than ideal testing instruments. Studies have suggested that environmental differences that exist between races are extremely important in IQ determination. For instance, data from the Minnesota Transracial Adoption Study reported by Scarr and Weinberg (1983) found that when African American children were adopted by White families at an early age, their IQs were more similar to the White IQ average of 110, compared with an average of 90 for African American children reared in the Black community. However, the African American adopted children still scored 6 points below the White children in the same family. Scarr and Weinberg concluded that genetic differences between the races cannot be used exclusively to explain IQ differences. |
For reviews of The Bell Curve by Herrnstein and Murray,
Connect to these sites:
Interview with Robert Sternberg
Reviews of The Bell Curve from Contemporary Psychology, May 1995
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