Race differences in intelligence
If we are able to draw strong conclusions concerning genetic factors involved in social class intelligence differences, why are we any less able to do so in conlparing racial groups? In terms of genetic criteria, social classes anc1 racial groups differ only in degree - both are breeding populatiolls which differ in gene frequencies for various characteristics. 1~he essential difference that concerns us is in the factors that influence social mobility. The main factor in upward mobility within racial groups is ability of one kind or another, including intelligence. Thus mobility and assortative mating based to some extent on ability make for SES stratification within racial groups a:nd a corresponding, though imperfect, segregation of those genetic factors associated with mobility in the SES hierarchy. This mO'vement is vertical within racial groups, but does not necessarily cut across racial boundaries. Thus, a certain SES status within the framework of one racial group cannot necessarily be directly equated with the corresponding status within a different racial group. As Eckland (1967, p. 191) has put it:
Both social classes and races can be treated as Mendelian populations. On the other hand, when describing . . . the selecting and sorting mechanisms that increase the betweengroup variance in intelligence, whites and Negroes cannot be thought of as being joined in this selection process. For all practical purposes, the fact persists that the American Negro, owing to discriminatory practices, is part of an adjacent but clearly separate structure which makes any comparisons of
phenotypic traits between Negroes and whites especially tenuous, except for skin color. (This is not true of social classes within either structure.) Differences in gene frequencies among SES groups, furthermore,
are more or less directly attributable to the selecting and sorting mechanisms involved in social mobility. The much larger variety of genetic differences among racial groups, on the other hand, has much more obscure origins tracing back through the history of the race for hundreds or thousands of generations and has involved a host of selective factors other than those involved in social mobility since the industrial revolution. Genetically selective factors, such as differences in climatic and social adaptation, mayor may not involve genes which are relevant to present-day social mobility. Yet it seems more likely than not that some of the cultural adaptations in the past history of a racial group would have genetically selective effects which could make for racial differences, on the average, in educability and types of occupational performance. Spuhler and Lindzey (1967, p. 412) have noted
. . . the enormous discrepancies between races in the efficiency with which culture is transmitted (for example, the difference between literate and nonliterate societies). Some of these differences are closely associated with race differences, have existed for many thousands of years, and presumably have been accompanied by very different selection pressures in regard to characters potentially relevant to culture transmission, such as 'intelligence'.