Jensen, Arthur

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Jensen, Arthur 1923–

Arthur R. Jensen was born on August 24, 1923, in San Diego, California. He joined the faculty of the University of California, Berkeley, in 1958 and became the center of a major controversy in 1969 when his article “How Much Can We Boost IQ and Academic Achievement?” was published in the Harvard Educational Review.

Jensen argued that Americans socially classified as black and white had, on average, different genetic potentials for intelligence, which he identified with IQ. He concluded that if black and white Americans enjoyed environments of equal quality, blacks would reduce their 15-point IQ deficit (compared to whites) to only about 10 points. In his later works he introduced the concept of “g,” sometimes called the “general intelligence factor,” which measures the tendency of some people to do better (or worse) than others on a whole range of mental tasks. This tendency becomes more marked as the cognitive complexity of the task increases and Jensen notes that blacks tend to fall farther below whites when the “g-loading,” or cognitive complexity, of an IQ test increases.

At Berkeley, the immediate reaction to Jensen’s views was several weeks of violent demonstrations, and protests continued to flare periodically throughout the 1970s. He defended himself against charges of racism with four arguments:

  1. Setting race aside, “black” and “white” are socially significant groups in America. Blacks are identified for purposes of affirmative action (different standards of entry to universities) and public debate. For example, the principal of a school may be criticized if the children of black professionals do worse than most white students.
  2. There can be average genetic differences between socially constructed groups. For example, if people with higher intelligence become professionals and less intelligent people become unskilled workers, and if like tends to marry like, then a genetic difference for intelligence will emerge among social classes. This theme was later developed by Charles Murray and Richard Herrnstein in The Bell Curve (1994).
  3. The truth can never be racist, and whether two groups differ for genetic potential is a scientific question to be settled by evidence. Knowing the truth is important. If black and white children, on average, do have different genetic potentials for academic achievement, it may be unjust to criticize a school principal when an achievement gap exists.
  4. An average difference between groups does not justify discrimination against individuals because of their group membership. Jensen stresses that, even if his hypothesis is correct, under conditions of environmental equality the upper 25 percent of blacks would overlap with the upper 50 percent of whites for intelligence. Indeed, the brightest individual in America might be black.

The emotion that has surrounded Jensen’s hypothesis has largely overshadowed the evidence both for and against it. For example, after World War II, the children of black American soldiers and German women matched the IQs of children fathered by white soldiers and German women, irrespective of the g-loading of IQ tests. This fact is by no means decisive of the debate, but it illustrates that the debate can be carried on in terms of evidence rather than epithet. Jensen’s assessment of the evidence from postwar Germany appears in The g Factor (1998).

Emotion has also obscured the fact that had the IQ debate not occurred, certain advances in psychology might also not have occurred. For example, Jensen (1972) noted that identical twins have IQs far more alike than randomly selected individuals, which seems to show that genes are dominant and environment weak in determining intelligence. He calculated that the impotence of environment was such that the magnitude of the black-white IQ gap was too large to be purely environmental.

William Dickens and James Flynn responded to Jensen’s theories to this point with a model suggesting that people who are alike genetically tend to have environments that are atypically similar. Two individuals born with the physical traits of being fast and tall are both likely to be selected for basketball teams and get professional coaching. Similarly two individuals born with more mental ability than average are likely to have the benefits of greater teacher attention, honors classes, and attending good universities. In other words, even when identical twins are separated at birth, they will have more than genes in common: they will have life histories that show the same powerful environmental factors at work. They both will have enjoyed professional coaching, or both will have enjoyed highly superior educational experiences. The model’s mathematics demonstrated that large group differences in either basketball skills or IQ-test performance could be primarily environmental in origin. If correct, this would illuminate areas as diverse as special education and how to remain mentally acute in old age. The Jensen debate shows that racism and the scientific examination of group differences are two different things, and also that banning scientific debate always inhibits the pursuit of truth.

SEE ALSO Heritability; IQ and Testing.


Dickens, William T., and James R. Flynn. 2001. “Great Leap Forward.” New Scientist 170 (2287): 44–47.

Flynn, James R. 1980. Race, IQ, and Jensen. London: Routledge.

_____. 1999. “Searching for Justice: The Discovery of IQ Gains over Time.” American Psychologist 54 (1): 5–20.

Herrnstein, Richard J., and Charles Murray. 1994. The Bell Curve: Intelligence and Class Structure in American Life. New York: The Free Press.

Jensen, Arthur R. 1972. Genetics and Education. London: Methuen.

_____. 1998. The g Factor: The Science of Mental Ability. Westport, CT: Praeger.

James R. Flynn