Pathogenic diseases impose selection pressures on the social behaviour of host populations. In humans (Homo sapiens), many psychological phenomena appear to serve an antipathogen defence function. One broad implication is the existence of cross-cultural differences in human cognition and behaviour contingent upon the relative presence of pathogens in the local ecology. We focus specifically on one fundamental cultural variable: differences in individualistic versus collectivist values. We suggest that specific behavioural manifestations of collectivism (e.g. ethnocentrism, conformity) can inhibit the transmission of pathogens; and so we hypothesize that collectivism (compared with individualism) will more often characterize cultures in regions that have historically had higher prevalence of pathogens. Drawing on epidemiological data and the findings of worldwide cross-national surveys of individualism/collectivism, our results support this hypothesis: the regional prevalence of pathogens has a strong positive correlation with cultural indicators of collectivism and a strong negative correlation with individualism. The correlations remain significant even when controlling for potential confounding variables. These results help to explain the origin of a paradigmatic cross-cultural difference, and reveal previously undocumented consequences of pathogenic diseases on the variable nature of human societies.

Previous research has documented cross-cultural differences in personality traits, but the origins of those differences remain unknown. The authors investigate the possibility that these cultural differences can be traced, in part, to regional differences in the prevalence in infectious diseases. Three specific hypotheses are deduced, predicting negative relationships between disease prevalence and (a) unrestricted sociosexuality, (b) extraversion, and (c) openness to experience. These hypotheses were tested empirically with methods that employed epidemiological atlases in conjunction with personality data collected from individuals in dozens of countries worldwide. Results were consistent with all three hypotheses: In regions that have historically suffered from high levels of infectious diseases, people report lower mean levels of sociosexuality, extraversion, and openness. Alternative explanations are addressed, and possible underlying mechanisms are discussed.

Regional differences in disease prevalence are associated with a wide array of cross-cultural differences. However, the complex relationships among culture, disease, and other ecological variables remain underinvestigated. Future research into the origins of cultural differences will benefit from the availability of a numerical index identifying the extent to which infectious diseases have been historically prevalent within regions defined by geopolitical borders. This article introduces such an index. This index is based on disease prevalence data obtained from old epidemiological atlases and is calculated for 230 geopolitical regions (mostly nations) around the world.

What are the origins of cultural differences in conformity? The authors deduce the hypothesis that these cultural differences may reflect historical variability in the prevalence of disease-causing pathogens: Where pathogens were more prevalent, there were likely to emerge cultural norms promoting greater conformity. The authors conducted four tests of this hypothesis, using countries as units of analysis. Results support the pathogen prevalence hypothesis. Pathogen prevalence positively predicts cultural differences in effect sizes that emerge from behavioral conformity experiments (r .49, n 17) and in the percentage of the population who prioritize obedience (r .48, n 83). Pathogen prevalence also negatively predicted two indicators of tolerance for nonconformity: within-country dispositional variability (r -.48, n 33) and the percentage of the population who are left-handed (r -.73, n 20). Additional analyses address plausible alternative causal explanations. Discussion focuses on plausible underlying mechanisms (e.g., genetic, developmental, cognitive).

The behavioral immune system is a motivational system that helps minimize infection risk by changing cognition, affect, and behavior in ways that promote pathogen avoidance. In the current paper, we review foundational concepts of the behavioral immune system and provide a brief summary of recent social psychological research on this topic. Next, we highlight current conceptual and empirical limitations of this work and delineate important questions that have the potential to drive major advances in the field. These questions include predicting the ontological development of the behavioral immune system, specifying the relationship between this system and the physiological immune system, and distinguishing conditions that elicit direct effects of situational pathogen threats versus effects that occur only in interaction with dispositional disease concerns. This discussion highlights significant challenges and underexplored topics to be addressed by the next generation of behavioral immune system research.