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
POVERTY ACCOUNTS FOR GAP IN IQ SCORES BETWEEN BLACKS AND WHITES
The Bell Curve's one-sided analysis
EVANSTON, Ill. -- Contrary to "The Bell Curve" findings,
a new study by researchers at Columbia and Northwestern Universities
suggests that poverty and early learning opportunities -- not
race -- account for the gap in IQ scores between blacks and whites.
(The study will be published in the April  issue of Child Development.)
Adjustments for socioeconomic conditions almost completely eliminate
differences in IQ scores between black and white children, according
to the study's co-investigators. They include Jeanne Brooks-Gunn
and Pamela Klebanov of Columbia's Teachers College, and Greg Duncan
of the Center for Urban Affairs and Policy Research at Northwestern
As in many other studies, the black children in the study had
IQ scores a full 15 points lower than their white counterparts.
Poverty alone, the researchers found, accounted for 52 percent
of that difference, cutting it to 7 points. Controlling for the
children's home environment reduced the difference by another
28 percent, to a statistically insignificant 3 points -- in essence,
eliminating the gap altogether.
The study includes data from birth to age 5 on 800 black and white
children who were born premature and with a low birth weight.
Collected from eight health care sites around the country, it
is the only data set that combines high-quality measurement of
developmental outcomes (i.e., full-scale IQ tests) with longitudinal
data on family economic status, neighborhood conditions, family
structure and home environment. Because the study looks at very
young children, the subjects' IQ measures cannot be attributed
to such non-family influences as schooling or work.
"The study strongly suggests that economic and learning environments
of the home are the most powerful predictors of racial IQ differences
in 5-year-olds," said Brooks-Gunn.
The longitudinal data allowed the researchers to measure persistent
poverty -- found to be a key factor in the IQ differences. "Many
children have transitory experiences with poverty," said
Duncan. "For black children, poverty is likely to be much
more persistent," he said. Of the black children in the study,
40 percent lived in persistent poverty, compared to 5 percent
of white children.
The study also takes into account how impoverished neighborhood
conditions and environmental influences can affect even children
not living in poverty. Black families are more likely to live
in poor neighborhoods, whether or not they are poor themselves.
"Almost one half of all black children whose families were
not poor resided in poor neighborhoods, compared with less than
10 percent of white children," said Duncan.
In addition, the study measured other factors associated with
poverty that are more common in minority children. They include
characteristics related to family structure and resources: single
parents, parents with low educational levels and low literary
scores, unemployed parents and young parents.
To determine the child's level of stimulation in the home environment,
the data included measurements of parents' involvement and learning
and language experiences that they provided for their children.
For example, it measured whether the child has toys that teach
color, size and shape and whether the child is encouraged to learn
the alphabet and numbers.
Debate over what causes the IQ gap has been highly charged since
the 1994 publication of "The Bell Curve," by Richard
Hernstein and Charles Murray, who view the difference as genetic
and impossible to change.
The Bell Curve hypothesis does not depend on any direct
evidence, but rather on its authors' assertion that social and
economic factors cannot explain it. Because the typical black
ranks at the 15th percentile of the white IQ distribution, say
Hernstein and Murray, black socioeconomic status (SES) can only
explain the ranking if, on average, it is well below than the
15th percentile of white SES ranking.
The Bell Curve authors claim no such SES inequality exists, and
this is the point the Columbia-Northwestern study calls into question.
Most studies of socioeconomic status do not consider such obvious
factors as family income or neighborhood conditions, and those
that do fail to account for the degree of persistent poverty.
Three times as many black children as white children live in families
below the official U.S. poverty line. The average black child
in the United States lives in a family whose long-term income
ranks at about the ninth percentile of white income distribution,
according to the study. The percentile ranking for blacks drops
to about the fifth percentile of white income distribution when
adjusted for the very different neighborhood conditions black
and white children typically live in.
The significance of these factors, and the consequent finding
that the economic and learning environments of the home are the
most powerful predictors of age-5 racial IQ differences, is the
implication that the debate spawned by "The Bell Curve"
has badly misdirected the national debate on welfare reform.
Such reform is clearly needed, said Duncan, Brooks-Gunn and Klebanov,
but the point of reform should be to focus on the real problems
of children rather than the presumed moral failings of their parents.
Whatever the merits of requiring mandatory employment and responsible
behavior, the researchers said, the key issue -- and the one with
the greatest impact on the nation's future -- is how such requirements
will affect family poverty.
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
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.
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
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
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
Return to Overview
1. Press Release from Columbia and Northwestern Universities, April, 1996.
Contact: Pat Tremmel at (847) 491-4892 or firstname.lastname@example.org or
Barry Rosen at (212) 678-3176 or email@example.com .
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,
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.