In this study, we present a comparative sibling analysis. This enables us to test two major social mobility hypotheses, i.e. The modernization hypothesis and the socialist ideology hypothesis. We employ survey data on brothers in england, hungary, the netherlands, scotland, spain, and the usa, covering a historical period from 1916 till 1990. Results show that the effects of parental social class on educational attainment are smaller in technologically advanced societies, and that the effects of parental social class on occupational status are smaller in social-democratic and communist societies. In addition, the total family impact on occupational status declines with modernization. But overall, we observe that the family of origin has not lost its importance for its sons' educational attainment and occupational status yet.