Conspiratorial echoes of disease: The relationship between pathogen prevalence and conspiracy beliefs

Conspiracy beliefs vary substantially across countries and regions, yet the ecological factors underlying this variation remain largely unexplored. Drawing on behavioral immune system theory, which suggests that pathogen threat can heighten vigilance toward potential dangers, we examined whether pathogen prevalence predicts conspiracy beliefs. Study 1 analyzed four cross-national datasets (20-32 countries) and found that conspiracy beliefs were higher in countries with greater historical pathogen prevalence. Study 2 tested this relationship in a preregistered study using a larger sample (N = 15,503 from 55 countries) and found that historical pathogen prevalence predicted higher levels of conspiracy beliefs. Study 3 extended these findings to the US state level using data from 123,781 participants across 50 states. Finally, Study 4 (N = 493) experimentally manipulated perceived pathogen prevalence and found causal effects on generic and vaccine-related conspiracy beliefs. These findings extend behavioral immune system research by relating pathogen-rich ecologies to contemporary conspiracy thinking.