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 Stateswhich virtually
all scholars now agree to be approximately 15 pointsis 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
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 Murrays 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 Emorys 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 Polignanos 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 IQsa plausible hypothesis that
certainly cannot be ruled out on the basis of existing evidencethen
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
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.
Polignanos 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.