The Twenty Years' War

"Intelligence" may offer the clearest example we have of how ideology can corrupt social science. Although the topic has been politicized by both left and right, during the last generation the ideological pressures have come almost entirely from the left, and along these lines: that intelligence is essentially the product of experience—above all, the nature of the child's environment—the genes having little to do with it; group differences in test performance are spurious, contrived to favor the socially privileged; the meaning of intelligence is in any case unclear; and the methods of measuring it inadequate and likely to be prejudicial.

This indictment reflects a more general aversion towards heredity, intelligence being only one of a large number of qualities where a genetic influence is denied. Until recently, schizophrenia was thought to be produced by pathological childrearing, despite much evidence for a significant biological influence. When the infantile autism disorder (the "Rain Man" syndrome) was diagnosed in the 1940's, it was also taken to be the result of a disturbed upbringing—in this case, by a "refrigerator mother." This assumption, especially, illustrates vividly the power of dogma over observation, as significant features of the syndrome point to a strictly neurological explanation.

Although fierce environmentalism has given way where severe mental...

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