Race differences in average IQ are largely genetic


Race differences in average IQ are largely genetic
Medical Research News
Published: Tuesday, 26-Apr-2005

A 60-page review of the scientific evidence, some based on state-of-the-art magnetic resonance imaging (MRI) of brain size, has concluded that race differences in average IQ are largely genetic.

The lead article in the June 2005 issue of Psychology, Public Policy and Law, a journal of the American Psychological Association, examined 10 categories of research evidence from around the world to contrast “a hereditarian model (50% genetic-50% cultural) and a culture-only model (0% genetic-100% cultural).”

The paper, “Thirty Years of Research on Race Differences in Cognitive Ability,” by J. Philippe Rushton of the University of Western Ontario and Arthur R. Jensen of the University of California at Berkeley, appeared with a positive commentary by Linda Gottfredson of the University of Delaware, three critical ones (by Robert Sternberg of Yale University, Richard Nisbett of the University of Michigan, and Lisa Suzuki & Joshua Aronson of New York University), and the authors’ reply.

“Neither the existence nor the size of race differences in IQ are a matter of dispute, only their cause,” write the authors. The Black-White difference has been found consistently from the time of the massive World War I Army testing of 90 years ago to a massive study of over 6 million corporate, military, and higher-education test-takers in 2001.

“Race differences show up by 3 years of age, even after matching on maternal education and other variables,” said Rushton. “Therefore they cannot be due to poor education since this has not yet begun to exert an effect. That’s why Jensen and I looked at the genetic hypothesis in detail. We examined 10 categories of evidence.”

The Worldwide Pattern of IQ Scores. East Asians average higher on IQ tests than Whites, both in the U. S. and in Asia, even though IQ tests were developed for use in the Euro-American culture. Around the world, the average IQ for East Asians centers around 106; for Whites, about 100; and for Blacks about 85 in the U.S. and 70 in sub-Saharan Africa.

Race Differences are Most Pronounced on Tests that Best Measure the General Intelligence Factor (g). Black-White differences, for example, are larger on the Backward Digit Span test than on the less g loaded Forward Digit Span test.

The Gene-Environment Architecture of IQ is the Same in all Races, and Race Differences are Most Pronounced on More Heritable Abilities. Studies of Black, White, and East Asian twins, for example, show the heritability of IQ is 50% or higher in all races.

Brain Size Differences. Studies using magnetic resonance imaging (MRI) find a correlation of brain size with IQ of about 0.40. Larger brains contain more neurons and synapses and process information faster. Race differences in brain size are present at birth. By adulthood, East Asians average 1 cubic inch more cranial capacity than Whites who average 5 cubic inches more than Blacks.

Trans-Racial Adoption Studies. Race differences in IQ remain following adoption by White middle class parents. East Asians grow to average higher IQs than Whites while Blacks score lower. The Minnesota Trans-Racial Adoption Study followed children to age 17 and found race differences were even greater than at age 7: White children, 106; Mixed-Race children, 99; and Black children, 89.

Racial Admixture Studies. Black children with lighter skin, for example, average higher IQ scores. In South Africa, the IQ of the mixed-race “Colored” population averages 85, intermediate to the African 70 and White 100.

IQ Scores of Blacks and Whites Regress toward the Averages of Their Race. Parents pass on only some exceptional genes to offspring so parents with very high IQs tend to have more average children. Black and White children with parents of IQ 115 move to different averages–Blacks toward 85 and Whites to 100.

Race Differences in Other “Life-History” Traits. East Asians and Blacks consistently fall at two ends of a continuum with Whites intermediate on 60 measures of maturation, personality, reproduction, and social organization. For example, Black children sit, crawl, walk, and put on their clothes earlier than Whites or East Asians.

Race Differences and the Out-of-Africa theory of Human Origins. East Asian-White-Black differences fit the theory that modern humans arose in Africa about 100,000 years ago and expanded northward. During prolonged winters there was evolutionary selection for higher IQ created by problems of raising children, gathering and storing food, gaining shelter, and making clothes.

Do Culture-Only Theories Explain the Data? Culture-only theories do not explain the highly consistent pattern of race differences in IQ, especially the East Asian data. No interventions such as ending segregation, introducing school busing, or “Head Start” programs have reduced the gaps as culture-only theory would predict.

In their article, Rushton and Jensen also address some of the policy issues that stem from their conclusions. Their main recommendation is that people be treated as individuals, not as members of groups. They emphasized that their paper pertains only to average differences. They also called for the need to accurately inform the public about the true nature of individual and group differences, genetics and evolutionary biology.

Rushton and Jensen are well-known for research on racial differences in intelligence. Jensen hypothesized a genetic basis for Black-White IQ differences in his 1969 Harvard Educational Review article. His later books Bias in Mental Tests (1980) and The g Factor (1998), as well as Rushton’s (1995) Race, Evolution, and Behavior, show that tests are not biased against English speaking minorities and that Black-White-East Asian differences in brain size and IQ belong in an evolutionary framework.


3 thoughts on “Race differences in average IQ are largely genetic”

  1. The paper in question was, in fact, published in Psychology, Public Policy, and Law, a journal of the APA. The full text is available here (PDF).

    This topic of racial differences is sensitive, mainly because of the history of baseless and harsh discrimination in the United States, as well as the fascist German eugenics programs, and others. But just because there has been a past history of racial stereotypes, it does not necessarily follow that there are no genetic differences.

    As some of you may have noticed, I have a tendency to submit articles that explore biological differences based on gender or sexual orientation. I do this, because I believe there are intrinsic differences between male/female and straight/gay. Yet these topics are taboo because of the stereotyping and discrimation brought against women and homosexuals. In order to break the stereotypes and end the discrimination, it was/is necessary for women and homosexuals to insist on strict equality—to the point where any mention of genetic differences is quickly squashed, regardless of their merit.

    The topic of this post is similarly sensitive. Any mention of genetic racial differences, especially one that supports the old stereotypes, is automatically assumed to be racist and unfounded. Please do not jump to this conclusion. Read the study and decide for yourselves whether or not this article is newsworthy.

  2. My biggest gripe regarding this article is one which is ignored over and over again in many such papers. Although they admit that it is an issue early in the paper, the entire article is based on an assumption that there is a particular “black” genetic profile, something which can hardly be assumed.

    Like almost all species, the human race has the greatest genetic diversity near its point of origin, and Africa has an incredible amount of genetic diversity. The so-called “black race” encompasses a huge range of genetic variance, which is obvious to even a casual observer in terms of the vast spectrum of morphological differences. Nearly the only common factor is a darker-than-white skin color, though it’s worth noting that there is a wide variance for that, too. Is there variance for intelligence? Presumably…there is clearly a genetic component to intelligence, and there’s variance for everything else genetic.  But the idea that one can lump descendents of all African stocks into one black category, and compare that to all people with white skin is inherently flawed.

    The paper also seems to assume that lightness or darkness of skin is an indicator of proportion of “black” genes, an assumption which is also flawed. A relatively small (certainly compared to the number of genes which might have conceivable impacts on intelligence) suite of genes influence skin color, and after a few generations recombination would render such an assumption completely invalid. I know couples whose children display a surprising range of skin colors, within just a single family.

    I also must say that while I don’t have any specific reason not to trust any of them, I worry a bit whenever I see a paper on race citing many anatomical and social science papers on racial issues published around the turn of the century, when such research was thoroughly pervaded by racism and inherent bias. Many similar papers published in that era have been thoroughly discredited.

    I remain (though skeptically) open to the idea of link between race and intelligence, but this doesn’t convince me.

  3. …in case you were wondering if there might be any bias in the authors of the study, you might noted that Rushton has been quoted as attributing German military prowess to the purity of their gene pool, and stating that small brains in black men are a trade off for large penises.

Comments are closed.