![]() ![]() As noted above, one of the costs of group living is the potentially high level of conflict and aggression that occurs among group members, which involves greater energy expenditure, risk of injury, and chronic stress. Thus when they reach adulthood they will have learned what they can and cannot do, and thereby fit into the social fabric of their social group (Pereira & Fairbanks 1993).įinally, sociality in and of itself appears to carry benefits for individuals. For example, during social play juveniles receive reinforcement from adults about how dominance hierarchies work, and what it means to have a given rank within a social group of a given species. In social groups, infants and juveniles play with one another, which develops motor skills as well as the social skills necessary to survive and reproduce in a social setting. Moreover, sociality allows cooperative socialization of offspring. Group-living animals simply choose mates within their social group. Animals that do not live in groups must either search for mates or opportunistically mate when they encounter other individuals. In addition, sociality is beneficial to group-living animals in that it makes it easier for them to find mates. Group members will also benefit from cooperation over defense of food-or other limited resources such as water holes and sleeping sites-as groups can out-compete individuals, and larger groups can out-compete smaller groups (Wrangham 1980). In groups, there are many individuals looking for food simultaneously and thus detection of good food resources (e.g., ripe fruit Figure 2) will inevitably be communicated to others simply because group members are usually in close proximity to one another. Sociality also benefits animals via access to food and other resources. Third, individuals in groups can collectively mob predators and successfully drive them away, whereas lone individuals cannot. Second, living in a group decreases each individual's chance of being preyed upon due to an effect called "geometry for the selfish herd" (Hamilton 1971): this states that the larger the group (e.g., 100 versus 10), the lower each individual's chance (1/100 versus 1/10) of becoming prey. First, in social groups there are more individuals looking out for predators and thus predators will be detected more quickly. Probably most importantly, living in a group likely decreases one's risk of falling victim to predation (van Schaik 1983). Given all of these potential costs of group living, why do so many primates-and other mammals-bother living in groups at all? One might especially wonder about this for the lowest-ranking individuals in a social group (i.e., those who are last in line for the available resources).ĭespite the costs, sociality is important to these animals for several reasons. Finally, groups may be disadvantageous because they are more easily detectable by predators compared to solitary individuals. In addition to these social costs of group living, close social contact also increases the potential transmission of pathogens, which increases each individual's risk of contracting infectious diseases. Other socially-induced events may also increase stress levels: in chacma baboons, for example, infanticidal (infant killing) behavior by males-or even simply the immigration of a potentially infanticidal male into a social group-increases stress hormone levels in females with infants (Engh et al. Chronic stress can adversely affect health and reproduction in numerous ways (Sapolsky 2002). In addition to energy costs and risk of injury, high levels of aggression-given or received-can lead to chronic psychological stress. While usually mediated by dominance hierarchies in which higher-ranking individuals have priority of access to limited resources, aggressive competition over food and mates is common in primates, and is not only energetically costly but can lead to injury and even death (Mason & Mendoza 1993). Individuals must share food resources, water resources, sleeping sites, and mates. Group life carries with it inevitable conflict and competition. ![]()
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