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Like many other animals, human beings engage in behavioral defenses against infectious pathogens. The behavioral immune system consists of a suite of psychological mechanisms that (a) detect cues connoting the presence of infectious pathogens in the immediate environment, (b) trigger disease-relevant emotional and cognitive responses, and thus (c) facilitate behavioral avoidance of pathogen infection. However, the system responds to an overly general set of superficial cues, which can result in aversive responses to things (including people) that pose no actual threat of pathogen infection. In addition, the system is flexible, such that more strongly aversive responses occur under conditions in which perceivers are (or merely perceive themselves to be) more vulnerable to pathogen infection. Recent research reveals many provocative implications-for the experience of disgust, for extraversion and social interaction, for xenophobia and other prejudices, and for the origins of cultural differences.

From evolutionary psychological reasoning, we derived the hypothesis that chronic and contextually aroused feelings of vulnerability to disease motivate negative reactions to foreign peoples. The hypothesis was tested and supported across four correlational studies: chronic disease worries predicted implicit cognitions associating foreign outgroups with danger, and also predicted less positive attitudes toward foreign (but not familiar) immigrant groups. The hypothesis also received support in two experiments in which the salience of contagious disease was manipulated: participants under high disease-salience conditions expressed less positive attitudes toward foreign (but not familiar) immigrants and were more likely to endorse policies that would favor the immigration of familiar rather than foreign peoples. These results reveal a previously under-explored influence on xenophobic attitudes, and suggest interesting linkages between evolved disease-avoidance mechanisms and contemporary social cognition.

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People who are more avoidant of pathogens are more politically conservative, as are nations with greater parasite stress. In the current research, we test two prominent hypotheses that have been proposed as explanations for these relationships. The first, which is an intragroup account, holds that these relationships between pathogens and politics are based on motivations to adhere to local norms, which are sometimes shaped by cultural evolution to have pathogenneutralizing properties. The second, which is an intergroup account, holds that these same relationships are based on motivations to avoid contact with outgroups, who might pose greater infectious disease threats than ingroup members. Results from a study surveying 11,501 participants across 30 nations are more consistent with the intragroup account than with the intergroup account. National parasite stress relates to traditionalism (an aspect of conservatism especially related to adherence to group norms) but not to social dominance orientation (SDO; an aspect of conservatism especially related to endorsements of intergroup barriers and negativity toward ethnic and racial outgroups). Further, individual differences in pathogen-avoidance motives (i.e., disgust sensitivity) relate more strongly to traditionalism than to SDO within the 30 nations.political ideology | pathogens | disgust | culture | evolutionary psychology T he costs imposed by pathogens on their hosts have spurred the evolution of complex antipathogen defenses, many of which are behavioral (1, 2). In humans, such defenses range from the proximate avoidance of pathogen cues to the execution of complex rituals, often with far-reaching consequences (3). At the individual level, functionally specialized psychological mechanisms detect pathogen cues and motivate avoidance of physical contact with pathogens [e.g., via the emotion of disgust (4)]. These mechanisms, which have been collectively referred to as the behavioral immune system, influence, among other things, mate preferences (5, 6), dietary preferences (7), and person perception (8) (summarized in Significance Pathogens, and antipathogen behavioral strategies, affect myriad aspects of human behavior. Recent findings suggest that antipathogen strategies relate to political attitudes, with more ideologically conservative individuals reporting more disgust toward pathogen cues, and with higher parasite stress nations being, on average, more conservative. However, no research has yet adjudicated between two theoretical accounts proposed to explain these relationships between pathogens and politics. We find that national parasite stress and individual disgust sensitivity relate more strongly to adherence to traditional norms than they relate to support for barriers between social groups. These results suggest that the relationship between pathogens and politics reflects intragroup motivations more than intergroup motivations.