Person:

Benenson, Joyce

Theoretical models based on primate evidence suggest that social structure determines the costs and benefits of particular aggressive strategies. In humans, males more than females interact in groups of unrelated same-sex peers, and larger group size predicts success in inter-group contests. In marked contrast, human females form isolated one-on-one relationships with fewer instrumental benefits, so social exclusion constitutes a more useful strategy. If this model is accurate, then human social exclusion should be utilized by females more than males and females should be more sensitive to its occurrence. Here we present four studies supporting this model. In Study 1, using a computerized game with fictitious opponents, we demonstrate that females are more willing than males to socially exclude a temporary ally. In Study 2, females report more actual incidents of social exclusion than males do. In Study 3, females perceive cues revealing social exclusion more rapidly than males do. Finally, in Study 4, females’ heart rate increases more than males’ in response to social exclusion. Together, results indicate that social exclusion is a strategy well-tailored to human females’ social structure.

Few experimental studies investigate the mechanisms by which young children develop sex-typed activity preferences. Gender self-labeling followed by selective imitation of same-sex models currently is considered a primary socialization mechanism. Research with prenatally androgenized girls and non-human primates also suggests an innate male preference for activities that involve propulsive movement. Here we show that before children can label themselves by gender, 6- to 9-month-old male infants are more likely than female infants to imitate propulsive movements. Further, male infants’ increase in propulsive movement was linearly related to proportion of time viewing a male model’s propulsive movements. We propose that male sex-typed behavior develops from socialization mechanisms that build on a male predisposition to imitate propulsive motion.

Many forms of judgments, such as those used in economic games or measures of social comparison, require understanding relative value, as well as the more complex ability to make comparisons between relative values. To examine whether young children can accurately compare relative values, we presented children 4 to 7 years with simple judgments of relative value in two scenarios. Children then were asked to compare the relative values in the two scenarios. Results show that even the youngest children downgraded evaluations of a reward when another has a larger amount, indicating the ability to make relative value judgments. When asked to compare relative values however, only the oldest children were able to make these comparisons consistently. We then extended this analysis to economic game performance. Specifically, previous results using economic games suggest that younger children are more generous than older ones. We replicate this result, and then show that a simple change in procedure, based on the initial study, is sufficient to change young children’s choices. Our results strongly suggest that conclusions regarding young children’s pro-social motives based on relative value comparisons should be viewed cautiously.

Studies on human cooperation using economic games rarely include ecologically relevant factors. In studies on non-human primates however, both status and sex typically influence patterns of cooperation. Across primate species, high status individuals are more likely to cooperate, though this depends on the species-specific social structure of each sex. Based on human social structure, we predict that higher status males who interact more in hierarchical groups than females, will invest more than high status females in valued same-sex peers after successful cooperation. Across three studies, 187 male and 188 female participants cooperated with a (fictitious) same-sex partner who varied in competence. Participants then divided a reward between themselves and their partner. High status was induced in three different ways in each study, social influence, leadership and power. No overall sex difference in reward sharing was observed. Consistent with the hypothesis however, across all three studies, high status males invested more than high status females in cooperative partners, suggesting that high status males intuitively evaluate sharing rewards with same-sex partners as more beneficial.

The nature of ancestral human social structure and the circumstances in which men or women tend to be more cooperative are subjects of intense debate. The male warrior hypothesis proposes that success in intergroup contests has been vital in human evolution and that men therefore must engage in maximally effective intragroup cooperation [1–3]. Post-conflict affiliation between opponents is further proposed to facilitate future cooperation [4], which has been demonstrated in non-human primates [5] and humans [6]. The sex that invests more in post-conflict affiliation, therefore, should cooperate more. Supportive evidence comes from chimpanzees, a close genetic relative to humans that also engages in male intergroup aggression [7]. Here we apply this principle to humans by testing the hypothesis that among members of a large community, following a conflict, males are predisposed to be more ready than females to repair their relationship via friendly contact. We took high-level sports matches as a proxy for intragroup conflict, because they occur within a large organization and constitute semi-naturalistic, standardized, aggressive, and intense confrontations. Duration or frequency of peaceful physical contacts served as the measure of post-conflict affiliation because they are strongly associated with pro-social intentions [8, 9]. Across tennis, table tennis, badminton, and boxing, with participants from 44 countries, duration of post-conflict affiliation was longer for males than females. Our results indicate that unrelated human males are more predisposed than females to invest in a behavior, post-conflict affiliation, that is expected to facilitate future intragroup cooperation.

Across species, cooperative alliances must withstand internal tensions. The mechanisms by which allies respond to competing against one another have been studied extensively in non-human animals, but much less so in humans. In non-human species, affiliative physical contact and close proximity immediately following a contest are utilized to define reconciliation between opponents. The proportion of conflicts that are reconciled however differs markedly by species and sex. The purpose of this study was to examine whether, like many other social species, humans utilize physical contact and close proximity following a competition between friends, and if so, whether one sex is more likely to exhibit these behaviors. Using a standardized procedure, two same-gender friends competed against one another producing a clear winner and loser. Prior to and following the competition, the friends relaxed together. Videotapes of the relaxation periods showed that male friends spent more time than female friends engaged in affiliative physical contact and close proximity both before and after the competition, but not during a brief intervening cooperative task. These results suggest that in the face of competing self-interests, physical contact and close proximity facilitate repair of males’ more than females’ valuable relationships.