RUSHTON REVIEWS JENSEN'S G FACTOR
review of The g Factor just appeared in Politics and the Life
Sciences, 1998, 17, 230-232
Date sent: Tue, 23 Mar 1999 12:06:55 -0500
From: "J. P. Rushton"
To: Ian Pitchford
Copies to: Chanburr@aol.com, firstname.lastname@example.org
Subject: [h-bd] Review of Arthur Jensen's The g Factor
This review of The g Factor just appeared in Politics and the Life
Sciences, 1998, 17, 230-232. I believe Steve S. posted his review earlier
from National Review but now wonder if Jensen's new book is worth a
focused discussion by H-BD Members?
The g Factor: The Science of Mental Ability
Arthur R. Jensen
Westport, CT: Praeger, 1998, 700pp, $39.95 hdbk.
Reviewed by J. Philippe Rushton who is Professor of Psychology at the
University of Western Ontario, London, Ontario N6A 5C2, Canada. His most
recent book is Race, Evolution, and Behavior(1995, Transaction).
Few scientists have effects or laws named after them. Arthur Jensen's
listed in a number of dictionaries as an "ism!" The Random House and
Webster's Unabridged Dictionaries contain the following entry:
Jen-sen-ism (jen´se niz´em), n. the theory that an individual's IQ
largely due to heredity, including racial heritage. [1965-1970]; after
Arthur R. Jensen (born 1923), U.S. educational psychologist, who proposed
such a theory; see -ism] --Jen´sen-ist, Jen´sen-ite´, n., adj.
The "theory" attributed to Jensen has, in fact, been around since the
Francis Galton (1822-1911), whose Hereditary Genius (1869) predated by
exactly one century Jensen's famous Harvard Educational Review article
that led him to be labeled a "hereditarian." The dictionary definition
can't be overly derided, however, as Jensen's (1969) review of the
evidence that IQ is heritable and that genetic factors are involved in the
Black-White IQ gap had enormous impact.
Jensenism, one of the great heresies of 20th century science, is partly
responsible for getting the Darwinian-Galtonian paradigm back on track in
differential psychology after it had been derailed in the behavioral
sciences for at least a generation following World War II. In a brilliant
40-year career that has earned him a place among the most frequently cited
figures in contemporary psychology, Arthur Jensen has systematically
researched and extended Charles Spearman's (1927) seminal concept of g,
the general factor of intelligence. The g Factor is an awesome and
monumental exposition of the case for the reality of g. It does not draw
back from its most controversial conclusions -- that the average
differences in IQ found between Blacks and Whites has a substantial
hereditary component, and that this difference has important societal
However, The g Factor is not about race, as such. The first five chapters
with the intellectual history of the discovery of g and various models of
how to conceptualize intelligence. Other chapters deal with the biological
correlates of g (excluding race), its heritability, and its practical
predictive power. The fact that psychometric g has many physical
correlates proves that it is not just a methodological artifact. Among
biological variables, gloads on heritability coefficients determined from
twin studies and inbreeding depression scores calculated in children born
from cousin-marriages. g is also related to brain size measured by
Magnetic Resonance Imaging (MRI), brain evoked potentials, and
intracellular brain pH levels. It (g) is a product of human evolution and
is also found in non-human animals.
Despite these caveats, The Bell Curve affair allows one to safely predict
g Factor's coverage of race will strike many as of central importance. All
the issues Jensen raised in 1969 are still with us today. Indeed, much of
the opposition to IQ testing and heritability would probably disappear if
it were not for the stubborn and unwelcome fact that, despite extensive
well funded programs of intervention, the Black-White difference refuses
to go quietly into the night. Chapter 11 of The g Factor fully documents
that, on average, the American Black population scores below the White
population by about 1.2 standard deviations, equivalent to 18 IQ points.
(This magnitude of difference gives a median overlap of less than 15
percent, meaning that less than 15 percent of the Black population exceeds
the White average of 50 percent).
The difference between Blacks and Whites in average IQ scores has
over the past 80 years (despite some claims that the gap is narrowing) and
can be observed as early as three years of age. Controlling for overall
socioeconomic level only reduces the mean difference by 4 IQ points.
Culture-fair tests tend to give Blacks slightly lower scores, on the
average, than more conventional tests, as do non-verbal tests compared
with verbal tests, and abstract reasoning tests compared with tests of
acquired knowledge. On average, Blacks also score 1 standard deviation
below Whites in academic achievement throughout the period from grades 1
through 12 (and also considerably below all other disadvantaged minorities
tested — Puerto Rican, Mexican-American, and American Indian).
International IQ Distribution
Inspired by "Jensenism," researchers like Richard Lynn and Philip E.
only pushed the envelope, but extended the ‘outside of the envelope' and
made the race-IQ debate international in scope with their findings that
East Asians average higher on tests of mental ability than do Whites,
whereas Caribbeans (and especially Africans) average lower. East Asians,
measured in North America and in Pacific Rim countries, typically average
IQs in the range of 101 to 111. Caucasoid populations in North America,
Europe, and Australasia typically have average IQs from 85 to 115 with an
overall mean of 100. African populations living south of the Sahara, in
North America, in the Caribbean, and in Britain typically have mean IQs
from 70 to 90. (Blacks in sub-Saharan Africa score about 2 standard
deviations [approximately 30 IQ points] below the mean of Whites on
But the 18 point IQ difference between American Blacks and Whites is only
average. On some sub-tests the Black-White difference is smaller and on
other sub-tests the Black-White difference is larger. Black-White
differences are markedly smaller on tests of rote learning and short term
memory than on tests of reasoning and those requiring transformation of
the input. For example, on the Forward Digit Span Test, in which people
are asked to recall a series of digits in the same order as that in which
they were presented, Black-White differences are quite small, but on the
Backward Digit Span Test in which people recall a series of digits in the
reverse order to that in which they were presented, they are quite large.
One day, while re-reading Spearman's (1927) The Abilities of Man, Jensen
tells us that he noted the suggestion (which appears on page 379), that
Black-White differences on various tests are a function of each tests' g
loading. Here, Jensen thought, was the essential phenomenon that would
explain, in much broader, more fundamental terms, the specific
psychometric phenomenon that gave rise to the variation in the Black-White
The g Factor summarizes the results of numerous investigations of
hypothesis on a wide variety of psychometric tests administered to large
representative samples of Whites and Blacks. Chapter 11, for example,
describes the results from 17 independent data sets on a total of nearly
45,000 Blacks and 245,000 Whites derived from 171 psychometric tests.
gloadings consistently predict the magnitude of the Black-White difference
(r = +.63). Spearman's hypothesis is borne out even among three-year-olds
administered eight subtests of the Stanford-Binet. The rank correlation
between the g loadings and the Black-White differences is +.71 (p <.05).
These g related race differences are not due to factors such as the
the test, social class differences, or tautologies based on some
inevitability of factor analysis. Indeed, it is not even universally true
that all groups that differ, on average, in their overall score on a test
battery will conform to Spearman's hypothesis. In South Africa, although
the nearly 1 standard deviation difference between Whites and East Indians
showed no correlation between g loadings and standardized mean
differences, the 2 standard deviation difference between Whites and Blacks
showed a correlation of +.62.
Spearman's hypothesis even applies to the g factor extracted from
elementary cognitive tasks. In some of these studies, 9-to-12-year-olds
are asked to decide which of several lights is illuminated and move their
hand to press a button that turns that light off. All children can
perform the tasks in less than one second, but children with higher IQ
scores perform faster than do those with lower scores, and White children,
on average, perform faster than Black children. The correlations between
the g loadings of these types of reaction time tasks and the Black-White
differences range from +.70 to +.81.
Jensen also applied Spearman's hypothesis to East Asian-White comparisons
these same reaction time measures. The direction of the correlation is
opposite to that in the Black-White studies, indicating that, on average,
East Asians score higher in g than do Whites. No one so far seems to have
looked at East Asian-White differences on conventional psychometric tests
as a function of their g loadings. From the study just mentioned, however,
Jensen's prediction is clear: One should find the reverse of Spearman's
hypothesis for Black-White differences.
Are Race Differences Heritable?
Chapter 12 presents Jensen's technical arguments for why he believes that
differences are about 50 percent heritable. He emphasizes the fact that it
is precisely those components of intelligence tests that are most
heritable and that most relate to brain size which most profoundly
differentiate Blacks from Whites. Thus, Black-White differences on 11
sub-tests of the Wechsler Intelligence Scale for Children are predicted by
the amount of inbreeding depression on the same 11 sub-test scores from
Japan (r = +.48). The inbreeding prediction was a sufficiently robust
predictor to overcome generalization from the Japanese in Japan to Blacks
and Whites in the U.S. There really is no non-genetic explanation for the
inbreeding effect and its ability to predict Black-White differences in
scores on IQ tests.
The g Factor also cites the evidence of transracial adoption studies.
studies have been carried out on Korean and Vietnamese children adopted
into White American and White Belgian homes. Though many had been
hospitalized for malnutrition, prior to adoption, they went on to develop
IQs ten or more points higher than their adoptive national norms. By
contrast, Black and Mixed-Race (Black-White) children adopted into White
middle-class families typically perform at a lower level than similarly
adopted White children. In the well known Minnesota Transracial Adoption
Study, by age 17, adopted children with two White biological parents had
an average IQ of 106, adopted children with one Black and one White
biological parent averaged an IQ of 99, and adopted children with two
Black biological parents had an average IQ of 89.
The g Factor also devotes a fair amount of space to racial differences in
size. Chapter 6 reviewed the literature that found that the brain-size/IQ
relation was most clearly shown using Magnetic Resonance Imaging (r = .44
across eight separate studies). Chapter 12 documents the three-way racial
gradient in brain size established by aggregating data from studies using
four kinds of measurements: (a) wet brain weight at autopsy, (b) volume of
empty skulls using filler, (c) volume estimated from external head sizes,
and (d) volume estimated from external head measurements and corrected for
body size. East Asians and their descendants average about 17 cm3 (1 in3)
larger brain volumes than do Europeans and their descendants, whose brains
average about 80 cm3 (5 in3) larger than do those of Africans and their
descendants. Jensen calculated an "ecological" correlation (widely used in
epidemiological studies) of +0.99 between median IQ and mean cranial
capacity across the three populations of "Mongoloids," "Caucasoids," and
The g Factor also considers the race differences from an evolutionary
Jensen endorses the "Out-of-Africa" theory, that Homo sapiens arose in
Africa about 100,000 years ago, expanded beyond Africa after that, and
then migrated east after a European/East Asian split about 40,000 years
ago. Since evolutionary selection pressures were different in the hot
savanna where Africans evolved than in the cold Arctic where Mongoloids
evolved, these ecological differences had not only morphological, but also
behavioral effects. The farther north the populations migrated ‘Out of
Africa,' the more they encountered the cognitively demanding problems of
gathering and storing food, gaining shelter, making clothes, and raising
children during prolonged winters. As these populations evolved into
present-day Europeans and East Asians, they underwent selective pressure
for larger brains.
In recent years, the equalitarian dogma has run headlong into some bad
the wake of the success of The Bell Curve (Herrnstein & Murray, 1994), and
other recent books about race (including my own) to provide race-realist
answers to the question of differential group achievement, there has been
an intense effort to get the ‘race genie' back in the bottle, to get the
previously tabooed toothpaste back in the tube. By firmly establishing the
psychometric, neurophysiological, behavior genetic, and comparative
evidence for the existence and importance of Spearman's g, Jensen's The g
Factor makes it near certain that such efforts will end up shredded by
Galton, F. (1869). Hereditary genius. London: Macmillan.
Herrnstein, R.J., & Murray, C. (1994). The bell curve: Intelligence
structure in American life. New York: Free Press.
Jensen, A. R. (1969). How much can we boost IQ and scholastic
Harvard Educational Review, 39, 1-123.
Spearman, C. (1927). The abilities of man: Their nature and
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