This article uses a behavioral genetics approach to study gender differences in expressed political interest, applying the enriched environment hypothesis to gendered political socialization. As girls are less stimulated to develop an interest in politics than boys, we theorize that these differences in the socialization environment reduce the expression of girls' genetic predispositions compared to boys', leading to a gender gap in the heritability of this trait. Analyses using data on German twins (11–25 years) demonstrate relevant differences by gender and age in heritability estimates. While differences in political interest between boys are largely explained by genes, this is less the case for girls, as they have considerably higher shared environment estimates. Our results imply that gender differences in expressed political interest are sustained by both genetic variation and environmental influences (such as socialization), as well as the interaction between the two.