Married women with children experience greater intrasexual competition than their male counterparts.

Human males are considered to be more competitive than females. However, females must also compete for resources necessary for their own and their offsprings' survival. Since females use more indirect forms of competition than males, comparing observable forms of competition may be misleading. One critical driver of competition is resource asymmetry. Since competition occurs primarily within sex, reactions to resource asymmetry with same-sex peers should provide an important measure of competitiveness. We asked 596 married participants, 25-45 years of age with at least one child from three different countries to evaluate how same-sex individuals they know would react to a target individual who had a valuable resource that the same-sex individuals did not have. Half the participants evaluated reactions to same-sex targets, while the other half evaluated reactions to other-sex targets. Participants reported that women would react more negatively than men to resource asymmetry with same-sex targets, but not other-sex targets. These results suggest that women may be even more competitive than men in contexts when important resources related to reproductive success are at stake.

Females undergo selection too.

Extending Campbell's (1999) staying alive theory (SAT) beyond aggression, we reviewed evidence that females are more self-protective than males. Many commentators provided additional supporting data. Sex differences in life-history adaptations, in the optimal relation between survival and reproduction, and in the mechanisms underlying trade-offs involved with self-protection remain important topics with numerous opportunities for improved understanding.

Self-protection as an adaptive female strategy.

Many male traits are well explained by sexual selection theory as adaptations to mating competition and mate choice, whereas no unifying theory explains traits expressed more in females. Anne Campbell's "staying alive" theory proposed that human females produce stronger self-protective reactions than males to aggressive threats because self-protection tends to have higher fitness value for females than males. We examined whether Campbell's theory has more general applicability by considering whether human females respond with greater self-protectiveness than males to other threats beyond aggression. We searched the literature for physiological, behavioral, and emotional responses to major physical and social threats, and found consistent support for females' responding with greater self-protectiveness than males. Females mount stronger immune responses to many pathogens; experience a lower threshold to detect, and lesser tolerance of, pain; awaken more frequently at night; express greater concern about physically dangerous stimuli; exert more effort to avoid social conflicts; exhibit a personality style more focused on life's dangers; react to threats with greater fear, disgust, and sadness; and develop more threat-based clinical conditions than males. Our findings suggest that in relation to threat, human females have relatively heightened protective reactions compared to males. The pervasiveness of this result across multiple domains suggests that general mechanisms might exist underlying females' unique adaptations. An understanding of such processes would enhance knowledge of female health and well-being.

Girls exhibit greater empathy than boys following a minor accident.

Hundreds of studies find that girls and women report feeling greater empathy than boys and men in response to adverse events befalling others. Despite this, few non-self-report measures demonstrate similar sex differences. This produces the oft-cited conclusion that to conform to societal expectations of appropriate sex-typed behavior females report higher levels of empathy. Several studies of sex differences in areas of brain activation and on infants' and young children's behavior however provide suggestive findings that self-reports reflect actual underlying sex differences in experiencing concern about others. We demonstrate using behavioral indices that females experience more empathy than males after witnessing an adverse event befall a same-sex classmate. In our study, one member of a pair experienced a minor accident on the way to constructing a tower while a bystander observed. We measured whether bystanders ceased their ongoing activity, looked at the victim, waited for the victim to recover from the accident, and actively intervened to help the victim. Female more than male bystanders engaged in these activities. These behavioral results suggest that an adverse event produces different subjective experiences in females than males that motivate objectively different behaviors, consistent with findings from self-report measures of empathy.

Contest versus scramble competition: sex differences in the quest for status.

Both sexes benefit from attaining higher status than same-sex peers, but each sex employs distinctive competitive tactics. Men engage in conspicuous public contests for status and directly interfere with others' success. Despite frequent and intense contests which occasionally turn lethal, men typically employ ritualized tactics and accept status differentials within a group. More recently, research has examined women's subtle, safe, and often solitary, competitive tactics. Women's main competitive tactics consist of maintaining a few long-term alliances and gaining advantages when competitors are not present. When competitors are present, women utilize leveling, social exclusion, and low-cost forms of contest competition to best other women.

Gender differences in egalitarian behavior and attitudes in early childhood.

It is axiomatic that human females are more egalitarian than males. However, surprisingly little empirical research exists that empirically assesses this stereotype. We created two studies designed to objectively examine egalitarian behavior in 3- to 5-year-old children. In Study 1 we compared the egalitarian behavior and attitudes of American girls versus boys by tabulating the extent to which each gender awarded the same number of stickers to, and liked to the same degree, two puppets. One puppet followed the child's instructions or actions while the other did not during a drawing task in which the child played the roles of leader and peer. In the peer role, girls exhibited more egalitarian behavior than boys. In Study 2, French-Canadian children were shown two drawings by unknown peers-one messily and one neatly colored-, then asked to distribute stickers to each peer's drawing. Again, girls exhibited more egalitarian behavior than boys. Results suggest the origins of gender differences in egalitarian behavior occur early in life and merit further investigation.

Competition Elicits more Physical Affiliation between Male than Female Friends.

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.

High status males invest more than high status females in lower status same-sex collaborators.

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.

Cross-Cultural Sex Differences in Post-Conflict Affiliation following Sports Matches.

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.

Sex differences in human gregariousness.

Research on human sociality rarely includes kinship, social structure, sex, and familiarity, even though these variables influence sociality in non-human primates. However, cross-cultural ethnographic and observational studies with humans indicate that, beginning after age 5 years, males and females form differing social structures with unrelated individuals in a community. Specifically, compared with females, human males exhibit greater tolerance for and form larger, interconnected groups of peers which we term "gregariousness." To examine sex differences in gregariousness early in life when children first interact with peers without adult supervision, 3- to 6-year-old children were given the choice to enter one of three play areas: an empty one, one with an adult, or one with a familiar, same-sex peer. More males than females initially chose the play area with the same-sex peer, especially after age 5 years. Sex differences in gregariousness with same-sex peers likely constitute one facet of human sociality.

Do young children understand relative value comparisons?

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.

Human males appear more prepared than females to resolve conflicts with same-sex peers.

The aim of the study was to investigate sex differences in proximate mechanisms that precede the termination of conflicts. In Study 1, we asked women and men to report their intensity of anger in response to hypothetical, common transgressions involving a same-sex roommate. Direct verbal and physical aggression elicited the highest-intensity anger for both sexes, although overall women reported more intense anger than men to all transgressions. In Study 2, we examined sex differences in subjective and physiological reactions to a conflict using a role-playing scenario. Following recall of a conflict involving direct aggression and role-playing a reaction to it, compared with men, women reported their anger would dissipate less quickly and they would take longer to reconcile. Women also exhibited increased heart rate, but little change in cortisol, whereas men exhibited little change in heart rate but increased cortisol production. We interpret the results as indicating that women are less prepared than men to resolve a conflict with a same-sex peer.

The development of human female competition: allies and adversaries.

Throughout their lives, women provide for their own and their children's and grandchildren's needs and thus must minimize their risk of incurring physical harm. Alliances with individuals who will assist them in attaining these goals increase their probability of survival and reproductive success. High status in the community enhances access to physical resources and valuable allies. Kin, a mate, and affines share a mother's genetic interests, whereas unrelated women constitute primary competitors. From early childhood onwards, girls compete using strategies that minimize the risk of retaliation and reduce the strength of other girls. Girls' competitive strategies include avoiding direct interference with another girl's goals, disguising competition, competing overtly only from a position of high status in the community, enforcing equality within the female community and socially excluding other girls.

Social exclusion: more important to human females than males.

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.

Boys affiliate more than girls with a familiar same-sex peer.

Evidence from ethnographic, observational, and experimental studies with humans converges to suggest that males affiliate more than females with unrelated, familiar same-sex peers, but this has never been examined directly. With this aim, we compared frequency of affiliation with a single, randomly chosen, familiar same-sex peer for the two sexes during early childhood. A focal child was brought to a room with three play areas-one containing a same-sex peer, one containing an adult, and one empty-and time spent with the peer was tabulated. Results demonstrated that boys visited the play area with the same-sex peer more frequently than girls did, and more boys than girls spent significant amounts of time with the peer. Human males' greater willingness to affiliate with randomly chosen familiar peers likely contributes to sex differences in a number of characteristics of humans' social interactions.

Male more than female infants imitate propulsive motion.

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.

Under threat of social exclusion, females exclude more than males.

Theoretical analyses and studies with children suggest that females are more likely than males to respond to threats of social exclusion with exclusion. Here we present a series of studies using a modified version of a computerized competitive game that participants play against two fictitious opponents. In previous studies, females and males have typically made identical strategy choices when playing this game. We show that when players are told that the two fictitious opponents may form an exclusionary alliance against them, females modify their competitive strategies by forming more preventive exclusionary alliances than males do. These results support the idea that adult females are more likely than males to form preventive exclusionary alliances when faced with a social threat. The results further suggest that females and males compete in different ways.