The biological and social transmission of attitudes toward abortion and gay rights are analyzed in a large sample of adult twins, siblings, and their parents. We present a linear model for family resemblance allowing for both genetic and cultural transmission of attitudes from parents to offspring, as well as phenotypic assortative mating (the tendency to marry like) and other environmental sources of twin and sibling resemblance that do not depend on the attitudes of their parents. The model gives a close fit to the patterns of similarity between relatives for the two items. Results are consistent with a substantial role of genetic liability in the transmission of both attitudes. Contrary to the dominant paradigm of the social and political sciences, the kinship data are consistent with a relatively minor non-genetic impact of parental attitudes on the development of adult attitudes in their children. By contrast, the choice of mate is a social action that has a marked impact on the polarization of social attitudes and on the long-term influence that parents exert upon the next generation.