The science and politics of I.Q.

JL his book is concerned with a single major question: Are scores on intelligence tests (I.Q.'s) heritable? The answer, in the consensus view of most intelligence testers, is that about 80 percent of individual variation in LQ. scores is genetically determined. That is not a new conclusion. Pearson, writing in 1906, before the widespread use of the LQ. test, observed that "the influence of environment is nowhere more than one-fifth that of heredity, and quite possibly not one-tenth of it." 1 Herrnstein, reviewing the history of intelligence testing to 1971, concluded, "We may, therefore, say that 80 to 85 percent of the variation in LQ. among whites is due to the genes." 2 The present work arrives at two conclusions. The first stems from a detailed examination of the empirical evidence which has been adduced in support of the idea of heritability, and it can be stated simply. There exist no data which should lead a prudent man to accept the hypothesis that LQ. test scores are in any degree heritable. That conclusion is so much at odds with prevailing wisdom that it is necessary to ask, how can so many psychologists believe the opposite? The answer, I believe, is related to the second major conclusion of this work. The LQ. test in America, and the way in which we think about it, has been fostered by men committed to a particular social view. That view includes the belief that those on