In addition to geographical heterogeneity for major genetic markers in the population, there is also vertical differentiation in behavioral and physical characters with substantial heritabilities. This vertical differentiation arises from social stratification of the population based on occupational status.
IQ has a substantial heritability, is positively correlated with social class, and is related to social mobility.
Laboratory experiments [on Drosophila melanogaster] have confirmed the hypothesis that social mobility dependent to some extent on a variable with a substantial heritability will lead to genetic differences between groups.
It is argued that both genetic and environmental factors must be considered in any explanation of social class phenomena.
The reported associations between some major genetic markers and various quantitative characters suggest that both discontinuous and continuous genetic variation should be taken into account in future investigations concerned with genetic aspects of social stratification.
…1961 tested this hypothesis in a general population sample by comparing the IQs of fathers and sons and relating the differences to both upward and downward inter-generational social mobility. He found that a large proportion of social mobility was indeed related to IQ. 3 pilot inquiries carried out in Cambridge have produced consonant results. The experimental design has varied, as in each case there was an interest in some other questions besides social mobility, but all 3 surveys involved interviews and the use of the same intelligence tests with both fathers and sons; the results are summarized in Table 2: The results show that the movement between classes has more than restored the correlation between IQ and class that there was in the fathers’ generation—this perhaps being due to the changes in educational opportunities. All 3 surveys also showed that if the distance of movement was measured on a 6-point class scale, and related to the extent of the differences between the IQs of fathers and sons, the greater the difference in IQ the greater the distance of movement. In families in which the IQs of the father and two male sibs were known it was also found that the upwardly mobile sibs tended to have higher IQs than the non-mobile or downwardly mobile sibs (1970). Both verbal and performance components of the IQ were related to this social mobility (Gibson & Mascie-1973).
