Pathogens, Personality, and Culture: Disease Prevalence Predicts Worldwide Variability in Sociosexuality, Extraversion, and Openness to Experience Mark Schaller and Damian R. Murray University of British Columbia 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 sociosex- uality, (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. Keywords: culture, disease prevalence, extraversion, openness to experience, sociosexuality People’s personalities differ, and some of that individual vari- ability is geographically clumped. But why is that so? How are we to understand the origins of regional differences in personality? A complete response to that question will surely require attention to many different processes operating at different levels of analysis. Here, we focus on one previously unidentified contributor to those differences. We report empirical results indicating that specific kinds of cross-cultural differences in personality result, in part, from regional differences in the prevalence of infectious disease. Cross-Cultural Differences in Personality In recent years, several ambitious programs of research have collected data from dozens of countries worldwide as a means of documenting cross-cultural differences on various kinds of per- sonality traits. These investigations assessed personality traits at the individual level of analysis, with standard trait assessment instruments, and on the basis of these data computed mean trait scores at the regional level of analysis. For example, Schmitt (2005) and his collaborators in the Inter- national Sexuality Description Project assessed worldwide vari- ability in chronic tendencies toward either a “restricted” or “unre- stricted” sociosexual style. (Among other things, more highly unrestricted individuals seek more sexual variety, are more com- fortable with casual sexual encounters, and have more sexual partners across their lifetime.) The results document considerable regional variability on this trait. In addition, several international teams of researchers have assessed worldwide variability along the Big Five personality traits of agreeableness, conscientiousness, extraversion, neuroticism, and openness to experience (McCrae, 2002; McCrae, Terracciano, & 79 members of the Personality Profiles of Cultures Project, 2005; Schmitt et al., 2007). The results document regional differences along all five fundamental dimensions of personality. These results, and others like them, are invaluable assets to the scientific study of individual differences and culture. Newer in- vestigations have been addressing the consequences that these cultural differences may have (e.g., on health outcomes and social policy decisions; McCrae & Terracciano, 2008). To date, however, almost no research whatsoever has addressed why these worldwide differences in personality profiles exist in the first place. Psychology, Ecology, and the Origins of Culture Many factors may have contributed to cross-cultural differences in personality. Some of those causes may be idiosyncratic to the unique histories of specific populations. Although important, anal- yses of idiosyncratic circumstances don’t easily yield conclusions that are predictive on a more global scale. It is toward discovering a more complete (and more broadly predictive) explanation for the origins of cross-cultural differences that it is useful to consider how basic human tendencies, operating in conjunction with vary- ing ecological conditions, can produce cross-cultural differences Mark Schaller and Damian R. Murray, Department of Psychology, University of British Columbia, Vancouver, British Columbia, Canada. This research was supported by research grants from the University of British Columbia Hampton Fund and the Social Sciences and Humanities Research Council of Canada. Thanks to Emma Buchtel, Steve Heine, and Ara Norenzayan for helpful comments and suggestions. Thanks also to Robert McCrae, Antonio Terracciano, and their collaborators on the Per- sonality Profiles of Cultures Project for generously providing us with the opportunity to do secondary analyses on their facet-level findings prior to the publication of those findings. Correspondence concerning this article should be addressed to Mark Schaller, Department of Psychology, University of British Columbia, 2136 West Mall, Vancouver, British Columbia V6T 1Z4, Canada. E-mail: schaller@psych.ubc.ca Journal of Personality and Social Psychology Copyright 2008 by the American Psychological Association 2008, Vol. 95, No. 1, 212–221 0022-3514/08/$12.00 DOI: 10.1037/0022-3514.95.1.212 212