THE ORIGINS OF INDIVIDUAL-DIFFERENCES IN OCCUPATIONAL-STATUS AND EDUCATIONAL-LEVEL - A STUDY OF TWINS REARED APART AND TOGETHER

Sources of influences on educational and occupational achievement were investigated using the powerful combined twin/adoption design. Analyses for education were based on 331 pairs of twins reared apart (TRA) and 375 pairs of twins reared together (TRT). Analyses for occupation were based on fewer pairs. Maximum-likelihood model-fitting analyses revealed that environmental effects unique to the individual, environmental effects shared by the two twins in a pair and gentic effects all were important for individual differences. For both education and occupation, environmental effects were more important among women and genetic effects were more important among men. For education there were differences in the relative importance of the effects when the analyses were performed separately for cohorts under and above age 60. Consistent with a social change hypothesis, environmental influences were more important among older individuals than among younger, and, conversely, genetic influences seem to have a greater impact on education for the younger age group. Regression analyses revealed that the circumstances of separation among the reared apart twins probably have not biased the results. These results support accumulated evidence of the importance of genetic effects as a source of familial resemblance for socioeconomic status among men. The disparity in conclusions by sociologists and behavior geneticists from similar data is discussed.