DONDENA Seminar - Julián Costas-Fernández

Who interacts with whom shapes access to resources, opportunities, and wellbeing, yet the persistence of social networks remains poorly understood. This paper documents the long-run persistence of family-level ties in Latin America, tracing connections first established in Spain during the colonization of the Americas into the present day. Using biographical data on Spanish colonial migrants, we reconstruct historical family networks based on surname associations in Spain during colonization. We then link these to modern marriage patterns, identified through the joint distribution of surnames in full population data covering nearly 59 million individuals. Our analysis shows that colonial-era family ties remain remarkably persistent: families historically close in Spain are significantly more likely to intermarry today, even 500 years later. Part of this persistence is explained by historical and modern over-representation of homogamous marriages, nonetheless we still find sizeable persistence when we account for these. We document sizeable heterogeneity across locations in Latin America. Persistence is strongest in locations tied to colonial administration, and in areas with greater modern diversity. Finally, we compare our results with modern-day Spain.