Historical pathogen prevalence and the radius of trust

Why do people exhibit different levels of trust between strangers and those who are socially close to them? This study tests the hypothesis that societies with a historical prevalence of infectious diseases develop strategies to minimise contact with potentially unhealthy or contaminated out-groups, while emphasising strong local networks of in-groups to manage infections effectively, ultimately leading to a lower radius of trust. Our empirical analysis verifies that societies with higher historical pathogen prevalence trust less out-groups relatively to in-groups using (i) cross-country; (ii) cross-country individual-level; (iii) ethnic group-level; and (iv) individual-level data for a sample of second-generation migrants. In particular, our findings support a negative association between historical pathogen prevalence and the contemporary radius of trust, specifically when we differentiate attitudes between socially distant groups (e.g., people met for the first time) and family members. Furthermore, this pattern remains consistent when we proxy trust attitudes using historical data on disapproval of violence at the ethnic group level from the Standard Cross-Cultural Sample. We find that an increase in historical pathogen prevalence is associated with a lower disapproval of violence toward out-group members from other societies relative to in-group members from the local community. Overall, historical pathogen prevalence sheds light on a fundamental cultural trait that persists over time.