Class, genes, and rationality: A gene–environment interaction approach to ideology

Abstract Variation in political preferences is increasingly understood to stem from both environmental influences and genetics. Research in political psychology has argued that a pathway for genetic effects on ideology is via cognitive performance, showing a sizable genetic overlap between the traits. Yet the link between actual trait cognitive performance and economic conservatism is itself highly ambiguous, with both positive, null, and negative estimates prevalent in the literature. In this study, I argue that this puzzle can only be understood from a gene–environment interaction (GxE) perspective. Drawing on traditional theories of political preference formation, I argue that genetics associated with cognitive performance should cause more left‐wing economic preferences if you grow up in relative poverty, but more right‐wing economic preferences if you grow up affluent. Utilizing variation in a polygenic index (PGI) of cognitive performance within dizygotic twin pairs, coupled with unique register data on economic conditions for the twins, their parents, and their childhood neighborhood, I show that the causal effect of the PGI on economic conservatism is zero on average, but indeed sizable and sign‐discordant by class background. The GxE perspective thus has wide‐ranging implications for future research attempting to integrate genetic methods into political psychology.