Pre-print, Working paper: We study horizontal between-group cultural transmission using Stalin's ethnic deportations as a historical experiment. Over 2 million Soviet citizens, mostly Germans and Chechens, were forcibly relocated from the western to eastern parts of the USSR during WWII solely based on ethnicity. As a result, the native population of the deportation destinations was exogenously exposed to groups with drastically different gender norms and behavior. We combine historical and contemporary data to document that present-day gender equality in labor force participation, business leadership, and fertility as well as pro-gender-equality attitudes are higher among local native population of deportation destinations with a larger presence of Protestant compared to Muslim deportees. The effects are stronger for culturally closer groups and when adopting deportee norms is less costly. The results cannot be explained by selection, vertical cultural transmission, or deportee impact on the local economy. The evidence strongly suggests that gender norms diffused horizontally from deportees to the local population through imitation and learning.