http://www.indiana.edu/~intell/bellcurve.shtml
The Bell Curve rests on two distinctly different but sequential arguments, which together encompass the classic corpus of biological determinism as a social philosophy. The first argument rehashes the tenets of social Darwinism as it was originally constituted. Social Darwinism has often been used as a general term for any evolutionary argument about the biological basis of human differences, but the initial nineteenth century meaning referred to a specific theory of class stratification within industrial societies, and particularly to the idea that there was a permanently poor underclass consisting of genetically inferior people who had precipitated down into their inevitable fate. The theory arose from a paradox of egalitarianism: as long as people remain on top of the social heap by accident of a noble name or parental wealth, and as long as members of despised castes cannot rise no matter what their talents, social stratification will not reflect intellectual merit, and brilliance will be distributed across all classes; but when true equality of opportunity is attained, smart people rise and the lower classes become rigid, retaining only the intellectually incompetent.
This argument has attracted a variety of twentieth-century champions, including the Stanford psychologist Lewis M. Terman, who imported Alfred Binet's original test from France, developed the Stanford-Binet IQ test, and gave a hereditarian interpretation to the results (one that Binet had vigorously rejected in developing this style of test); Prime Minister Lee Kuan Yevv of Singapore, who tried to institute a eugenics program of rewarding well-educated women for higher birth rates; and Richard Herrnstein, a co-author of The Bell Curve and also the author of a 1971 Atlantic Monthly article that presented the same argument without the documentation. The general claim is neither uninteresting nor illogical, but it does require the validity of four shaky premises, all asserted (but hardly discussed or defended) by Herrnstein and Murray. Intelligence, in their formulation, must be depictable as a single number, capable of ranking people in linear order, genetically based, and effectively immutable. If any of these premises are false, their entire argument collapses. For example, if all are true except immutability, then programs for early intervention in education might work to boost IQ permanently, just as a pair of eyeglasses may correct a genetic defect in vision. The central argument of The Bell Curve fails because most of the premises are false.
