- 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
- "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.
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- Originally Published 4-26-5
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