Find Events Find People Find Jobs Find Sites Find Help Index


November 13, 2000

Race and IQ: What science says

Scott Lilienfeld and Irwin Waldman are associate professors of psychology

Few scientific issues are more incendiary than the question of race differences in IQ. The frequent reappearance of this politically charged issue, despite concerted efforts to suppress it, testifies to its importance.

This controversy was reignited on our campus by a recent column authored by Emory student Mike Polignano, which appeared in the Oct. 6 Emory Wheel. In this column, Polignano revived the question of whether the IQ difference between African Americans and whites in the United States—which virtually all scholars now agree to be approximately 15 points—is attributable to genetic influences.

Since its appearance, this column has provoked a great deal of heated disagreement. As psychology faculty at Emory, we wish to contribute to the ongoing discussion by lending a scientific perspective to this complex issue.

As Polignano noted, an open discussion of scientifically contentious issues is greatly preferable to a stifling of debate. We hope that all of us would vehemently oppose any efforts to suppress his views or those of any other members of the Emory community, regardless of how distasteful these views may be to some readers.

We believe it is especially important that free speech be protected and cherished at a university, given that the open exchange of differing viewpoints is an essential aspect of its mission. At the same time, it is crucial that faculty and students not prejudge the answers to difficult scientific questions before adequate data are available. Such opinions will be informed only to the extent that they are grounded in solid scientific data.

Reasoned and informed discussions of race differences in IQ have been hard to come by, even at Emory. The two of us vividly recall some of the acrimonious public debates that ensued on our campus following the publication of Herrnstein and Murray’s The Bell Curve in 1994. Many of these debates were short on scientific evidence and long on opinion, and tended to sacrifice substance on the altar of emotion. In one public forum sponsored by the Center for Ethics, an outside speaker launched into a vitriolic tirade replete with personal invectives toward Herrnstein and Murray. It was not one of Emory’s prouder moments.

So what can scientific findings tell us about the race difference in IQ? Whatever its origins, it is clear that this difference cannot be attributed to test bias. Several decades of research converge on the conclusion that IQ tests are equally valid measures of intelligence among African Americans and whites. Even Harvard paleontologist Stephen Jay Gould, one of the most outspoken critics of the view that race differences in IQ are genetically based, acknowledges that test bias in not a viable explanation for racial IQ discrepancies. We must look elsewhere to explain this vexing difference.

Polignano came down clearly on the side of a genetic explanation for this difference. But does the scientific evidence provide convincing support for his position? Based on our reading of the literature, we contend that it does not. Studies have shown that IQ is substantially influenced by genetic factors within both white and African American samples. It is worth noting, however, that these findings do not imply that the difference in IQ between whites and African Americans is genetically influenced. Regrettably, this often overlooked distinction was not mentioned in Polignano’s column.

Moreover, a number of studies suggest that the race difference in IQ may be substantially or perhaps entirely environmental in origin. For example, in a 1976 study of African Americans, Sandra Scarr and her colleagues examined the relationship between IQ and the proportion of genes indicative of African ancestry within subjects. If the race difference in IQ were genetically based, one would expect African Americans possessing more genes indicative of African ancestry to exhibit lower IQs than African Americans possessing fewer such genes. But Scarr and her colleagues found essentially no correlation between IQ and genes of African ancestry, calling into question the genetic hypothesis.

In 1994, one of us [Waldman] coauthored an article based on a followup of the Minnesota transracial adoption study, the largest-ever investigation of African American children raised in white middle-class homes. We reported that the IQs of transracial adoptees were significantly higher than both the African American and white population averages, thus strongly suggesting positive effects of the rearing environment on IQ, although these IQs were somewhat lower than those of adopted white children. In addition, when we controlled statistically for variables assessing adverse adoptive environment (e.g., number and quality of preadoptive placements, age at adoptive placement), the race difference in IQ decreased substantially.

These findings suggest, although do not prove, that the race difference in IQ may be largely a function of environmental disadvantage. Still other data collected in Germany following World War II indicate that the offspring of African American soldiers and white mothers possess IQs virtually identical to the white IQ average. Again, these findings argue against a genetic hypothesis for racial differences in IQ. Although the scientific jury is still out, there is little compelling evidence for this

If the race difference in IQ were in fact partly genetic, what would this finding mean? It is difficult to know. Even if there were a genetic component to this difference, it could be due to genes that code for physical attributes, such as skin color, that are unrelated to IQ per se.

In the United States, as in many other countries, there has been a longstanding pattern of discrimination against African Americans. If this discrimination contributes substantially to lower IQs—a plausible hypothesis that certainly cannot be ruled out on the basis of existing evidence—then the race difference in IQ would indeed be to some extent “genetic.” But this difference would be attributable not to genes that code for proteins relevant to IQ, but rather to genes that code for proteins relevant to skin color, which in turn influences the amount of discrimination that individuals encounter.

This phenomenon, called reactive gene-environment correlation, is notoriously difficult to disentangle from more direct genetic effects. Moreover, this phenomenon illustrates the complexities inherent in identifying and understanding the causes of race differences.

One common logical error, which Polignano committed, is to assume that if the race difference in IQ were genetically based, then environmental efforts aimed at eliminating this difference (e.g., affirmative action, Head Start) are doomed to failure. Nevertheless, it is well known that heritability does not imply immalleability or fixity. A characteristic can possess a heritability of 100 percent and yet be fully remediable by environmental interventions.

Perhaps the best known illustration of this point is phenylketonuria (PKU), a disease that oftenresults in profound mental retardation if left untreated. Al-though PKU is entirely genetic in origin, most of its severe physical and cognitive symptoms can be forestalled by early dietary intervention. The efficacy of such programs as affirmative action and Head Start is not dependent on an environmental basis for race differences in IQ. Instead, the efficacy of such programs must be evaluated on their own merits.

Polignano’s misstep regarding heritability and immalleability raises a broader issue with which we wish to conclude. Scientific findings do not dictate social policy, although they may at times inform it. No scientific findings regarding the origins of race differences in IQ could ever justify racism or discrimination against minority groups.

Scientific research concerning race differences is potentially important and should not be suppressed, regardless of the answers such research may yield. But such research is fortunately irrelevant to the crucial issue of whether all individuals should be treated with equal dignity irrespective of the color of their skin. Regardless of their diverse opinions regarding the controversial issues raised by Polignano, this is a point on which we hope all members of the Emory community can wholeheartedly agree.


Back to Emory Report Nov. 13, 2000