Tend and befriend

Tend-and-befriend is a critical, adaptive strategy that would have enhanced reproductive success among female cooperative breeders. Cooperative breeders are group-living animals where infant and juvenile care from non-mother helpers are essential to offspring survival.[10] Cooperative breeders include wolves, elephants, many nonhuman primates, and humans. Among all primates and most mammals, endocrinological and neural processes lead females to nurture infants, including unrelated infants, after being exposed long enough to infant signals.[11] Non-mother female wolves and wild dogs sometimes begin lactating to nurse the alpha female's pups.

Humans are born helpless and altricial, mature slowly, and depend on parental investment well into their young adult lives, and often even later.[11] Humans have spent most of human evolution as hunter-gatherer foragers. Among foraging societies without modern birth control methods, women tend to give birth about every four years during their reproductive lifespan.[11] When mothers give birth, they often have multiple dependent children in their care, who rely on adults for food and shelter for years. Such a reproductive strategy would not have been able to evolve if women did not have help from others. Allomothers (helpers who are not a child's mother) protect, provision, carry, and care for children.[11] Allomothers are usually a child's aunts, uncles, fathers, grandmothers, siblings, and other women in the community. Even in modern Western societies, parents often rely on family members, friends, and babysitters to help care for children. Burkart, Hrdy, and Van Schaik (2009) argue that cooperative breeding in humans may have led to the evolution of psychological adaptations for greater prosociality, enhanced social cognition, and cognitive abilities for cooperative purposes, including willingness to share mental states and shared intentionality.[10] These cognitive, prosocial processes brought on by cooperative breeding may have led to the emergence of culture and language.

Human and animal studies (reviewed in Taylor et al., 2000) suggest that oxytocin is the neuroendocrine mechanism underlying the female "befriend" stress response.[1] Oxytocin administration to rats and prairie voles increased social contact and social grooming behaviors, reduced stress, and lowered aggression. In humans, oxytocin promotes mother-infant attachments, romantic pair bonds, and friendships. Social contact or support during stressful times leads to lowered sympathetic and neuroendocrine stress responses. Although social support downregulates these physiological stress responses in both men and women, women are more likely to seek social contact during stress. Furthermore, support from another female provides enhanced stress-reducing benefits to women.[15] However, a review of female aggression noted that "The fact that OT [oxytocin] enhances, rather than diminishes, attention to potential threat in the environment casts doubt on the popular ‘tend-and-befriend’ hypothesis which is based on the presumed anxiolytic effect of OT".[16]

According to Taylor (2000), affiliative behaviors and tending activities reduce biological stress responses in both parents and offspring, thereby reducing stress-related health threats.[17] "Befriending" may lead to substantial mental and physical health benefits in times of stress. Social isolation is associated with significantly enhanced risk of mortality, whereas social support is tied to positive health outcomes, including reduced risk of illness and death.[18]

Women have higher life expectancies from birth in most countries where there is equal access to medical care.[19] In the United States, for example, this difference is almost 6 years. One hypothesis is that men's responses to stress (which include aggression, social withdrawal, and substance abuse) place them at risk for adverse health-related consequences.[20] In contrast, women's responses to stress, which include turning to social sources for support, may be protective to health.

Group living and affiliation with multiple unrelated others of the same sex (who do not share genetic interests) also presents the problem of competing for access to limited resources, such as social status, food, and mates. Interpersonal stress is the most common and distressing type of stress for women.[21] Although the befriending stress response may be especially activated for women under conditions of resource scarcity,[1] resource scarcity also entails more intense competition for these resources. In environments with a female-biased sex ratio, where males are a more limited resource, female-to-female competition for mates is intensified, sometimes even resorting to violence.[22] Although male crime rates far exceed those of females, arrests for assault among females follow a similar age distribution as in males, peaking for females in the late teens to mid-twenties. Those are ages in which females are at peak reproductive potential and experience the most mating competition. However, the benefits of affiliation would have outweighed the costs in order for tend-and-befriend to have evolved.

Rates of aggression between human males and females may not differ, but the patterns of aggression between the sexes do differ. Although females in general are less physically aggressive, they tend to engage in as much or even more indirect aggression (e.g. social exclusion, gossip, rumors, denigration).[23] When experimentally primed with a mating motive or status competition motive, men were more willing to become directly aggressive towards another man, whereas women were more likely to indirectly aggress against another woman in an aggression-provoking situation.[24] However, experimentally priming people with a resource competition motive increased direct aggression in both men and women. Consistent with this result, rates of violence and crime are higher among males and females under conditions of resource scarcity.[25] In contrast, resource competition did not increase direct aggression in either men or women when they were asked to imagine themselves married and with a young child. The costs of physical injury to a parent would also entail costs to his or her family.

Lower variance in reproductive success and higher costs of physical aggression may explain the lower rates of physical aggression among human females compared to males.[25] Females are in general more likely to produce offspring in their lifetimes than males. Therefore, they have less to gain from fighting and the risk of injury or death would produce greater fitness cost for females. The survival of young children depended more on maternal than paternal care, which underscores the importance of maternal safety, survival, and risk aversion.[25] Infants' primary attachment is to their mother, and maternal death increased the chances of childhood mortality in foraging societies by fivefold, compared to threefold in the cases of paternal death.[25] Therefore, women respond to threats by tending and befriending, and female aggression is often indirect and covert in nature to avoid retaliation and physical injury.

Women befriend others not only for protection, but also to form alliances to compete with outgroup members for resources, such as food, mates, and social and cultural resources (e.g. status, social positions, rights and responsibilities). Informational warfare is the strategic, competitive tactics taking the form of indirect, verbal aggression directed towards rivals.[26] Gossip is one such tactic, functioning to spread information that would damage the reputation of a competitor. There are several theories regarding gossip, including social bonding and group cohesion. However, consistent with informational warfare theory, the content of gossip is relevant to the context in which competition is occurring. For example, when competing for a work promotion, people were more likely to spread negative work-related information about a competitor to coworkers.[26] Negative gossip also increases with resource scarcity and higher resource value. In addition, people are more likely to spread negative information about potential rivals but more likely to pass on positive information about family members and friends.

As mentioned above, befriending can serve to protect women from threats, including harm from other people. Such threats are not limited to physical harm but also include reputational damage. Women form friendships and alliances in part to compete for limited resources, and also in part to protect themselves from relational and reputational harm. The presence of friends and allies can help deter malicious gossip, due to an alliance's greater ability to retaliate, compared to a single individual's ability. Studies by Hess and Hagen (2009) show that the presence of a competitor's friend reduced people's tendencies to gossip about the competitor.[26] This effect was stronger when the friend was from the same competitive social environment (e.g. same workplace) than when the friend was from a nonrelevant social environment. Friends increase women's perceived capabilities for inflicting reputational harm on a rival as well as perceptions of defensive capabilities against indirect aggression.