Reciprocal altruism has been the backbone of research on the evolution of altruistic behaviour towards non-kin, but recent research has begun to apply costly signalling theory to this problem. In addition to signalling resources or abilities, public generosity could function as a costly signal of cooperative intent, benefiting altruists in terms of (i) better access to cooperative relationships and (ii) greater cooperation within those relationships. When future interaction partners can choose with whom they wish to interact, this could lead to competition to be more generous than others. Little empirical work has tested for the possible existence of this 'competitive altruism'. Using a cooperative monetary game with and without opportunities for partner choice and signalling cooperative intent, we show here that people actively compete to be more generous than others when they can benefit from being chosen for cooperative partnerships, and the most generous people are correspondingly chosen more often as cooperative partners. We also found evidence for increased scepticism of altruistic signals when the potential reputational benefits for dishonest signalling were high. Thus, this work supports the hypothesis that public generosity can be a signal of cooperative intent, which people sometimes 'fake' when conditions permit it.

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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.

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Public generosity may be a means to convincingly advertise one's good character. This hypothesis suggests that altruistic individuals will be desirable as romantic partners. Few studies have tested this prediction, and these showed mixed results. Some studies have found that altruism is not particularly attractive; other studies showed that altruism is attractive by contrasting descriptions of 'nice guys' with 'jerks'. The present study sought to resolve this debate by having participants read a series of experimentally manipulated vignettes of persons with corresponding photographs, such that altruistic vignettes were compared with control descriptions that differed only in the presence or absence of small hints of altruistic tendencies. Altruists were more desirable for long-term relationships than neutral individuals. Women also preferred altruists for single dates whereas men had no such preference. These results are discussed with regard to the idea that people (males in particular) signal their good character via generosity.

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