Study claims IQ differences at least 50% genetic

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.”

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. 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.

From Charles Darwin Research Institute

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98 thoughts on “Study claims IQ differences at least 50% genetic”

  1. All Numbers are Median Numbers (50% percentile)

    100, ONE HUNDRED

    100, One Hundred

    Half above 100/Half below 100.

    Median for house prices

    Median for computer prices

    Median IQ is standard 100, One Hundred.


    All these are median numbers at the 50% percentile.

    Half below 100/ Half above 100

  2. With our daily lives becoming more and more dependant on technology, people are no longer looking at themselves to solve the complex and even simple problems of life. 25% of the population has an IQ of 85! When 100 is considered smart! Our dependence on technology is limiting our need and desire to think for ourselves. Why add 105+82 in your head when you have a calculator? Why do you need to remember how to spell business when you have spell checker? Why? Because if you want to carry your head high, have more confidence and a better memory than ever before you need the eBook I Q Mind Brain Memory Self Help Library. I have personally read this book and was very impressed with the results, I install Remote Car Starters for a living and anyone who has been under the hood of a new car knows how much brain power it takes to remember and simply sort out all those wires. Now while this book WILL NOT turn you into Einstein it will help you to focus your mind and train it as you would any muscle in your body. It is also a tremendous resource for parents who are trying to give their teen that something extra, before they enter the world of college.

  3. Items like this are troubling. So much of what makes us, us, is influenced by genetics that sure, why wouldn’t intelligence be as well? On the other hand, the racism you mention must also play a role. Finally, this goal, or ideal of a high IQ, what’s it good for, in a biological sense? Let’s say green people are genetically inclined to a lower IQ than blues. Well, they’re both still reproducing, buying color TVs, eating at Wendy’s and most importantly, reproducing.

    I guess this study’s biggest plus is it stirs the pot and gets people talking.

  4. It seams reasonable that intelligence is in part genetic and that separate gene pools would show differences in intelligence.

    However I wonder how much of this g difference is down to the racism weaved into the fiber of our world. Would it surprise aliens that the decedents of slaves still regarded as 2nd or 3rd class score lower on the white mans tests ?

    You cannot underestimate the impact of expectation and suggestion on these tests.

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