This study presents a comparative sibling analysis. This allows for the testing of 2 major social mobility hypotheses: the modernization hypothesis and the socialist ideology hypothesis. Survey data on brothers in England, Hungary, the Netherlands, Scotland, Spain, and the US is employed, covering a historical period from 1916 until 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, it is observed that the family of origin has not lost its importance for its sons' educational attainment and occupational status yet.