Arthur R. Jensen (2000) Mixing up Eugenics and Galton's Legacy to Research on Intelligence. Psycoloquy: 11(017) Intelligence g Factor (30)

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Psycoloquy 11(017): Mixing up Eugenics and Galton's Legacy to Research on Intelligence

Reply to Fancher on Jensen on Intelligence-g-Factor

Arthur R. Jensen
Educational Psychology
School of Education
University of California
Berkeley, CA 94720-1670


The fact that Sir Francis Galton coined the word 'eugenics' and promoted the concept during the latter part of his long life is hardly a disgrace, but it is apparently thought by some to sully his contributions as the founding father of differential psychology as an empirical science and to cast subsequent developments of Galton's original ideas in this sphere in a sinister light.


behavior genetics, cognitive modelling, evoked potentials, evolutionary psychology, factor analysis, g factor, heritability, individual differences, intelligence, IQ, neurometrics, psychometrics, psychophyiology, skills, Spearman, statistics
1. My aim in writing "The g Factor" (Jensen, 1998; 1999) was not to compile a history of the 'IQ controversy', or to recapitulate my earlier and often elaborate replies to critics of my former books and articles. I wanted to present as clear a picture as I could of the g factor, which has figured so prominently in the research on human abilities, and to explicate recent developments in empirical research on g. I believe that the Galton-Spearman line of thought about human abilities is now the mainline research in differential psychology, and I hope my book contributes to its advancement. My critics have been largely either ideological or scientifically technical. I pay little attention to the former but much attention to the latter.

2. Galton (1822-1911) is one of the most biographed figures in the history of psychology. Only the psychoanalyst has had more written about him. The variety and durability of Galton's ideas are truly remarkable and can't be diminished by the fact that there are currently some disapproving observations and reactions about the experiences gained in his extensive explorations in subSaharan Africa in the 1840s (Burt, 1962). But among biographies of famous scientists, particularly such near-psychopaths as Newton and Leibniz, Galton's personal conduct and ethical ideals seem exemplary by comparison. In any case, in science, unlike politics, a scientist's personality, beliefs, and convictions, although possibly of biographical and historical interest, are wholly separate from the objective validity of the scientist's discoveries, empirically testable theories, and methodological innovations.

3. Fancher (1999, par. #3) is waving a red flag by bringing up that fashionably vilifying word "eugenics" in the context of my book, which deals exclusively with the science of individual differences in mental abilities. The aspect of Galton's career that is most relevant to the subject of my book is not eugenics, which was a benign conception as initiated by Galton, but rather his extraordinary curiosity, inventiveness, and investigative zeal, which generated empirical discoveries of historic scientific importance and laid the foundations for differential psychology, psychometrics, and behavior genetics. True, he later promoted eugenics as a secular religion, with the express goal of increasing the future well-being of humanity. Galton took it for granted that superior mental and behavioral capacities as well as physical health and stamina are beneficial both to individuals and to the whole society.

4. In Galton's later years (he lived to 90) his scientific contributions became so amalgamated with his enthusiasm for eugenics as to have contributed to the disfavor in which Galtonian lines of research on human intelligence have been held in the latter half of the 20th century, during which we have seen a systematic inculcation in the public's mind of a link between the humane conception Galton termed 'eugenics,' on the one hand, and the fanatical political abuses and terrible acts committed in its name that were exposed at the end of World War II, on the other. This confusion has contributed to stigamatizing biological and genetical research on intelligence to a degree not seen in scientific research for any other natural phenomena, save perhaps for evolution as perceived by Biblical Fundamentalists.

5. What does not seem to be entirely clear, perhaps even to Galton himself, and to Fancher (1999), is that prescriptive eugenics falls not in the province of science, but in that of ethics or moral philosophy. Despite Galton's humanitarian aims, the desirability of eugenics is an ethical question rather than a scientific one. Science deals with what is, not with what anyone thinks ought to be. This critical distinction in no way discredits the eugenics concept or suggests that its aims, means, or feasibility should be divorced from scientific scrutiny. The same distinction must be made between medical science and medical practice, especially as biomedical technology advances. Galton himself mainly advocated negative eugenics, which today, in fact, is a principal aim of genetic counseling as respectably practiced in many medical centers around the world.

6. Galton's conception of eugenics is probably best expressed in his own words: "Individuals appear to me as partial detachments from the Infinite ocean of Being, and this world is a stage on which Evolution takes place, principally hitherto by means of Natural Selection, which achieves the good of the whole with scant regard to that of the individual. Man is gifted with pity and other kindly feelings; he has also to power of preventing many kinds of suffering. I conceive it to fall well within his province to replace Natural Selection by other processes that are more merciful and not less effective. This is precisely the aim of Eugenics. Its first object is to check the birth-rate of the Unfit, instead of allowing them to come into being, though doomed in large numbers to perish prematurely. The second object is the improvement of the race by furthering the productivity of the Fit by early marriages and healthful rearing of their children. Natural Selection rests upon excessive production and wholesale destruction; Eugenics on bringing no more individuals into the world than can be properly cared for, and those only of the best stock" (Galton, 1908, p. 323).

7. My critics have had no effect on the estimates of IQ heritability that I have reported at different times in various references, contrary to Fancher's (1999, par. #4) surmise. These estimates, like all statistical estimates of population parameters, vary in different samples and studies for a multitude of reasons - sample characteristics (e.g., age and range of ability), and psychometric characteristics of the tests. I discovered, for example, that the degree of heritability of mental tests is directly related to the tests' g loadings, further indicating that it is g, more than any other factor, that reflects the biological basis of individual differences in IQ. Whenever I have reported heritability estimates, they have been based on the average of the existing data at the time I am writing, but omitting, since 1975, the questionable data of Burt's studies of MZ twins reared apart. The overall average estimate of heritability based on monozygotic twins reared apart (excluding Burt's data) is .75. Burt's estimate was .77. Hence, averaging in Burt's figure with that of other studies or omitting it makes hardly any difference. In recent years, it has been discovered that IQ heritability increases with age, ranging from about .40 in childhood to about .65 -.70 in middle age and about .80 in the elderly. I have accordingly concluded that an overall average value of the broad heritability is rather uninformative compared to values which specify the age group, the types of kinship samples used, and the g-loadedness of the test scores used.

8. More is known about the genetic component of IQ variance than about the environmental component, most of which, by late adolescence, is NOT attributable to differences between family environments, but consists of nongenetic variance WITHIN families. It appears that most of this nongenetic variance results from what I call micro-environmental influences, which may consist largely of a multitude of virtually random small prenatal, perinatal, and postnatal environmental variables that have effects on the nongenetic but biological basis of mental development (Jensen, 1997). If this is true, it helps explain the failure of psychological and educational interventions to importantly and durably effect increases of the level of the g component of IQ tests. The secular increase in IQ (or Flynn Effect)would accordingly be explainable largely in terms of the intergenerational elimination of many of the most undesirable effects of the microenvironment by means that have affected virtually the whole population of the industrialized world, such as improved nutrition, advances in obstetrics, and inoculations that have virtually eliminated many childhood diseases.

9. I have always taken it for granted that the state of knowledge at the cutting edge of any science is provisional, as Fancher (1999, par. #7) points out, and that continual hypothesis testing is the scaffolding by which the theoretical structures for explaining empirical phenomena become generally accepted as true in a scientific sense. This has never implied any kind of Eternal Truth, which may exist only in pure mathematics and religion. While recognizing the provisional character of empirical knowledge at any given time, I doubt that equivocation on every point in its exposition is the most effective strategy for the advancement of research. Of what use to the development of a field is a book without an argument? The Science Citation Index and the Social Science Citation Index would seem to indicate that much of my work over the past three decades has indeed received, in Fancher's words, "wide and serious debate."


Burt, C. (1962). Francis Galton and his contributions to psychology. British Journal of Statistical Psychology, 15, 1-49.

Fancher, R.E. (1999). A historian's look at The g Factor. PSYCOLOQUY 10(58) psyc.99.10.058.intelligence-g-factor.8.fancher

Galton, F. (1908). Memories of my life. London: Methuen.

Jensen, A.R. (1997). The puzzle of nongenetic variance. In R.J. Sternberg & E.L. Grigorenko (Eds.), Heredity, intelligence, and environment (pp. 42-88). Cambridge: Cambridge University Press.

Jensen, A.R. (1998). The g factor: The science of mental ability. Westport, CT: Praeger.

Jensen, A.R. (1999). Precis of: "The g Factor: The Science of Mental Ability" PSYCOLOQUY 10(23). psyc.99.10.023.intelligence-g-factor.1.jensen

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