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Mischievous Tests. But behavioral scientists are less willing to define with Jensen's confidence the comparative roles of heredity and environment in human intelligence. "I agree that it is foolish to deny the possibility of significant genetic differences between races," writes James F. Crow, a population geneticist at the University of Wisconsin, in a response to the Jensen article commissioned by Harvard's Review. "But this is not to say that the magnitude and direction of genetic racial differences are predictable." In American society, he adds, the environmental difference between being black and being white could of itself account for the IQ gap.
This possibility appears to gain support from a well-known study by Geneticists Irving I. Gottesman and James Shields, which was not cited by Jensen, of 38 pairs of identical white twins. Separated in infancy, these twins were reared in different environments. Gottesman and Shields found that, since the twins were presumed to be genetic equals, the environmental factor alone must have accounted for a spread of 14 IQ points—almost the same gap that separates black and white.
Until instruments more precise than the IQ test are developed, any attempt to rank the intelligence of black and white is meaningless—and is bound to be mischievous in the light of its political implications. Too little is known of the genes to justify positive statements about their contribution to the intelligence of mankind at large, much less to any division of mankind. The suspicion that there are genetically determined differences at birth, and that these may contribute to the enormous diversity of the human intellect, is at least as old as Plato. But, as Geneticist Lederberg observes, "it remains just a hypothesis, and we are not much better equipped than Plato was to assess it."