Friend or fomite: Interpersonal value regulates infection-risky social contact across 61 societies

Proceedings of the National Academy of Sciences of the United States of America. 2026.

Sun H., Spadaro G., Pelica S., Kamiloğlu R., Abrahams L., Ackerman J., Grigoryev D., Tybur J.

Interpersonal contact is essential for cooperation and care, but it also provides a route for pathogen transmission between individuals. Hence, a key challenge for social organisms involves maintaining beneficial social contact while also limiting exposure to infection risks. Existing proposals suggest that this trade-off is guided by the interpersonal value of specific social targets. In addition, ecological and cultural factors including historical pathogen prevalence, individualism collectivism, tightness-looseness, and relational mobility might also shape how people avoid pathogens. To test whether and how infection-risky social contact varies with individual-level interpersonal value and these societal-level factors, we collected data from 61 societies (N = 42,756). Participants were randomly assigned to imagine targets who varied in interpersonal value, then rated their comfort with infection-risky contact with that target (e.g., drinking from the same water bottle) and whether they would touch the target when greeting them. In all societies, participants were more comfortable with infection-risky contact and more likely to engage in physical contact during greetings with targets of higher interpersonal value. Such associations varied only modestly across societies. Notably, the associations between infection-risky contact and societal-level factors depended on target interpersonal value and were concentrated among high-value targets – contact was lower where historical pathogen prevalence and tightness were greater, and higher where individualism and relational mobility were greater. These findings suggest that infection-risky contact is primarily guided by the value of social targets, with ecological and cultural factors playing a lesser role.

Keywords: interpersonal contacts, evolutionary psychology, disease transmission, interpersonal value