Arthur R. Jensen’s research while affiliated with University of California, Berkeley and other places

This essay describes Rushton’s contribution to examining the nexus of intelligence, race, and genetics, specifically what I termed “Spearman’s hypothesis”. It states that Black–White differences are “most marked in just those [tests] which are known to be saturated with g”. I (Jensen) had confirmed this hypothesis using large data sets in the 1970s and 1980s and also found that Black–White differences were most marked on the more heritable rather than the more cultural subtests. Rushton confirmed and extended these findings in many highly innovative ways and demonstrated Spearman’s hypothesis applied among samples of Gypsy Roma in Serbia, and East Asian, European, South Asian, Colored and Black samples in South Africa. He has not only documented group differences in brain size, intelligence, life span, family structure, infant mortality, developmental precocity, personality, and temperament, and rates of two egg twinning, and crime among East Asians, Europeans, and Africans, but also provided a life history theory that explains them.

This article is a critique on M. W. Smith’s “Alfred Binet’s remarkable questions: A cross-national and cross-temporal analysis of the cultural biases built into the Stanford-Binet Intelligence Scale and other Binet tests,” published in Genetic Psychology Monographs, 1974, 89, 307-334.

Recent theory and research has focused on the relationship between speed of performing elementary cognitive operations and general intelligence. The developers of the British Ability Scales (BAS) included the Speed of Information Processing (SOIP) subtest as a measure of mental processing speed. To test the validity of the SOIP subtest, a group of 12-year-old children were given the BAS short-form, including the SOIP subtest, and a series of electronically timed reaction time (RT) tasks. Correlations between RT and SOIP were higher than correlations between RT and other BAS subtests, suggesting convergent and discriminant validity. A hierarchical factor analysis of the data shows that the BAS SOIP subtest is related more to speed of apprehension (RT) than to speed of making the motor response, or movement time (MT).

In this Editorial we correct the false claim that g loadings and inbreeding depression scores correlate with the secular gains in IQ. This claim has been used to render the logic of heritable g a “red herring” and an “absurdity” as an explanation of Black–White differences because secular gains are environmental in origin. In point of fact, while g loadings and inbreeding depression scores on the 11 subtests of the Wechsler Intelligence Scale for Children correlate significantly positively with Black–White differences (0.61 and 0.48, P < 0.001), they correlate significantly negatively (or not at all) with the secular gains (mean r = −0.33, P < 0.001; and 0.13, ns, respectively). Moreover, heritabilities calculated from twins also correlate with the g loadings (r = 0.99, P < 0.001 for the estimated true correlation), providing biological evidence for a true genetic g, as opposed to a mere statistical g. While the secular gains are on g-loaded tests (such as the Wechsler), they are negatively correlated with the most g-loaded components of those tests. Also, the tests lose their g loadedness over time with training, retesting, and familiarity. In an analysis of mathematics and reading scores from tests such as the NAEP and Coleman Report over the last 54 years, we show that there has been no narrowing of the gap in either IQ scores or in educational achievement. From 1954 to 2008, Black 17-year-olds have consistently scored at about the level of White 14-year-olds, yielding IQ equivalents of 85 for 1954, 82 for 1965, 70 for 1975, and 81 for 2008. We conclude that predictions about the Black–White IQ gap narrowing as a result of the secular rise are unsupported. The (mostly heritable) cause of the one is not the (mostly environmental) cause of the other. The Flynn Effect (the secular rise in IQ) is not a Jensen Effect (because it does not occur on g).

We provide a detailed review of data from psychology, genetics, and neuroscience in a point-counterpoint for-mat to enable readers to identify the merits and demerits of each side of the debate over whether the culture-only (0% ge-netic-100% environmental) or nature + nurture model (50% genetic-50% environmental) best explains mean ethnic group differences in intelligence test scores: Jewish (mean IQ = 113), East Asian (106), White (100), Hispanic (90), South Asian (87), African American (85), and sub-Saharan African (70). We juxtapose Richard Nisbett's position, expressed in his book Intelligence and How to Get It, with our own, to examine his thesis that cultural factors alone are sufficient to explain the differences and that the nature + nurture model we have presented over the last 40 years is unnecessary. We review the evidence in 14 topics of contention: (1) data to be explained; (2) malleability of IQ test scores; (3) culture-loaded versus g-loaded tests; (4) stereotype threat, caste, and "X" factors; (5) reaction-time measures; (6) within-race heri-tability; (7) between-race heritability; (8) sub-Saharan African IQ scores; (9) race differences in brain size; (10) sex dif-ferences in brain size; (11) trans-racial adoption studies; (12) racial admixture studies; (13) regression to the mean effects; and (14) human origins research and life-history traits. We conclude that the preponderance of evidence demonstrates that in intelligence, brain size, and other life history traits, East Asians average higher than do Europeans who average higher do South Asians, African Americans, or sub-Saharan Africans. The group differences are between 50 and 80% heritable.

Recent editorials in this journal have defended the right of eminent biologist James Watson to raise the unpopular hypothesis that people of sub-Saharan African descent score lower, on average, than people of European or East Asian descent on tests of general intelligence. As those editorials imply, the scientific evidence is substantial in showing a genetic contribution to these differences. The unjustified ill treatment meted out to Watson therefore requires setting the record straight about the current state of the evidence on intelligence, race, and genetics. In this paper, we summarize our own previous reviews based on 10 categories of evidence: The worldwide distribution of test scores; the g factor of mental ability; heritability differences; brain size differences; trans-racial adoption studies; racial admixture studies; regression-to-the-mean effects; related life-history traits; human origins research; and the poverty of predictions from culture-only explanations. The preponderance of evidence demonstrates that in intelligence, brain size, and other life-history variables, East Asians average a higher IQ and larger brain than Europeans who average a higher IQ and larger brain than Africans. Further, these group differences are 50-80% heritable. These are facts, not opinions and science must be governed by data. There is no place for the "moralistic fallacy" that reality must conform to our social, political, or ethical desires.

General ability, defined as psychometric g, arises from the empirical fact that scores on various cognitive tests are positively correlated in the population. The g factor is highly stable across different factor analytic algorithms, across different test batteries and across different populations. Because all cognitive tests, from the simplest to the most complex, regardless of their informational content, are g-loaded to varying degrees, g cannot be described in terms of the tests' content, or even in psychological terms. It is actually a property of the brain. The loadings of various tests on g, from tests of sensory discrimination and reaction time to those of highly complex problem solving, predict those tests' degree of correlation with a number of non-psychometric variables: the test's heritability, inbreeding depression, coefficient of assortative mating, brain size, reaction time, brain nerve conduction velocity, brain glucose metabolic rate and features of brain evoked potentials. Although some of the brain's cognitive functions are modular, the g factor reflects the all-positive correlations among virtually all cognitive functions that show individual differences. I hypothesize that the brain contains no module for general problem solving. Correlations between individuals' performances in various cognitive tasks result from quantitative individual differences in physiological conditions that do not constitute the brain's modular and other neural design features but do influence their speed and efficiency of information processing.

Résumé De récents éditoriaux dans ce journal ont défendu le droit de l'éminent biologiste James Watson à soutenir l'hypothèse mal vue selon laquelle les populations d'origine subsaharienne obtiennent en moyenne aux tests d'intelligence générale des résultats inférieurs à ceux des populations d'origine européenne ou est-asiatique. Comme indiqué par ces éditoriaux, il existe des preuves scientifiques importantes démontrant que ces différences sont en partie d'origine génétique. Le traitement indigne infligé à Watson impose donc de faire le point sur l'état actuel des données sur l'intelligence, la race et la génétique. Dans le présent article, nous résumons nos précédentes revues fondées sur 10 catégories de preuves : la distribution mondiale des résultats aux tests ; le facteur g de capacité mentale ; les différences d'héritabilité ; les différences de taille du cerveau ; les études d'adoption transraciales ; les études sur les mélanges raciaux ; les effets de régression à la moyenne ; les traits liés à « l'histoire de vie » des sujets ; la recherche sur les origines humaines ; et la pauvreté des prévisions fournies par les explications fondées sur la culture seule. La majorité des données démontre qu'en matière d'intelligence, de taille du cerveau et d'autres paramètres de « l'histoire de vie », les Extrême-Orientaux ont un QI moyen supérieur et un cerveau plus gros que les Européens, qui ont un QI plus élevé et un cerveau plus volumineux que les Africains. De plus, ces différences entre groupes sont héritables dans des proportions allant de 50 à 80 %. Ce sont là des faits, pas des opinions, et la science doit être gouvernée par les données. Il n'y a pas place pour l'illusion moraliste selon laquelle la réalité doit se plier à nos désirs sociaux, politiques ou éthiques.