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correlations obtained for intelligence almost as precisely as it does for height," Jensen wrote. And yet, as several of his critics pointed out, the mean height in the United States and Japan has increased considerably in the last two centuries, too rapidly to be accounted for by genetic factors. Couldn't we expect the same of intelligence in an ideal learning environment?
Jensen conceded that there had been some general increase in height, but he proposed that it could be explained by the increased mobility among populations.
Outbreeding has increased at a steady rate ever since the introduction of the bicycle. For example, sons of parents who were from different Swiss villages were taller by approximately 1 inch than the sons of parents from the same village. The increase in heterozygosity, of course, eventually "saturates," and the effects level off, as has already occurred in the U.S. That genetic as well as nutritional factors are a major cause of the increase in actual height is further shown in the fact that approximately the same increase has occurred in all social classes in Western countries even though there have been nutritional differences among social classes.
Jensen concluded his argument: "Thus, the slight increase in the population's mean height over the last two centuriesthe environmentalists' favorite counter-argument to the high heritability of IQitself turns out to be largely a genetic phenomenon!"

 

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Obviously, if Jensen's premise were true, his solutiondividing students by lower and higher abilitieswould lead to schools that were resegregated along racial lines, this time because of supposed differences in student intelligence, rather than social discrimination. In fact, his argument was immediately enlisted by attorneys in a federal district court in a last-ditch effort to resist the desegregation of the Greensville and Caroline County, Virginia, public schools. The furor that resulted from the article was more personal than scholarly. For many years afterward, Jensen's mere appearance on a college campus would set off near riots.
In 1971, the psychologist Richard J. Herrnstein, confessing that he had been "submerged for twenty years in the depths of environmentalist behaviorism" as a former student of B. F. Skinner and a psychology professor at Harvard, wrote an equally provocative article simply titled "IQ" in the Atlantic Monthly . Herrnstein used much of the same material as Jensen (it became the basis for his book IQ and the Meritocracy and later The Bell Curve ). The New York Times quoted him as saying that his "conclusions, if true, amounted to a death sentence for the ideal of egalitarianism.'' Buttressed by Burt's formidable data from twin studies, the hereditarian argument appeared to have climbed out of the Nazi grave to which it had been consigned.
Within a month after Herrnstein's article appeared, he was invited to speak at Princeton University on an unrelated subject ("The visual field of the pigeon"), but he declined to attend when the university could not make what he thought were sufficient guarantees for his safety. In place of his lecture there was a forum on academic freedom. Herrnstein was defended by Leon Kamin, a psychology professor who had known him at Harvard when both were students there. Kamin, how-

 

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ever, was a behaviorist who believed that there was no plausible evidence that intelligence was genetically transmitted. Because Herrnstein cited Burt's famous separated-twin study, Kamin decided to read it for himself. Within ten minutes of starting to read Burt, Kamin decided that "it was transparently clear that the guy was a fraud." He noticed, for instance, that Burt had published several studies of separated twins over the years, beginning with twenty-one pairs in 1955, increasing to "over 30" pairs in 1958, and concluding with the fifty-three pairs in 1966. Despite the fact that the sample size more than doubled over the years, the heritability of