ABSTRACT
The objective prevalence of and subjective vulnerability to infectious diseases are associated with greater ingroup preference, conformity, and traditionalism. However, evidence directly testing the link between infectious diseases and political ideology and partisanship is lacking. Across four studies, including a large sample representative of the U.S. population (N > 12,000), we demonstrate that higher environmental levels of human transmissible diseases and avoidance of germs from human carriers predict conservative ideological and partisan preferences. During the COVID-19 pandemic (N = 848), we replicated this germ aversion finding and determined that these conservative preferences were primarily driven by avoidance of germs from outgroups (foreigners) rather than ingroups (locals). Moreover, socially conservative individuals expressed lower concerns of being susceptible to contracting infectious diseases during the pandemic and worried less about COVID-19. These effects were robust to individual-level and state-level controls. We discuss these findings in light of theory on parasite stress and the behavioral immune system and with regard to the political implications of the COVID-19 pandemic.