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6 Evolutionary Perspectives on the Links Between Close Social Bonds, Health, and Fitness--Joan B. Silk
Pages 121-144

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From page 121...
... Much of the work I discuss has been conducted on nonhuman primates. This taxonomic bias primarily reflects the fact that primatologists have a long history of interest in the complex dynamics of social relationships and commonly collect detailed information about the form, frequency, and sequence of interactions among individually identified animals with known reproductive histories.
From page 122...
... If highranking animals have priority of access to resources, and access to resources is an important component of survival and reproductive success, then a positive correlation between dominance rank and reproductive success and for selection to favor traits that enhance success in competitive encounters would be expected. Both these predictions are widely supported, although there are some interesting exceptions to the general patterns (Ellis, 1995; Clutton-Brock, 2009; Majolo et al., 2012)
From page 123...
... I then consider the mechanisms that underlie relationships between sociality and fitness outcomes, discussing both the direct benefits that animals may gain from their social partners (e.g., protection from predators) and the indirect benefits that they may derive from social ties (e.g., reduced stress levels)
From page 124...
... These results attracted considerable interest because they provided the first systematic evidence that social relationships are linked to reproductive success, and they suggest that investment in close social bonds has an adaptive payoff. However, the Amboseli analyses were vulnerable to several potential questions and criticisms: 1.
From page 125...
... I begin by discussing the methods we have developed for characterizing dyadic social bonds, and then discuss the structure of social bonds among female baboons in Amboseli and in a second population of baboons. DEFINING AND DOCUMENTING THE STRUCTURE OF SOCIAL RELATIONSHIPS Primatologists must take a different approach to studying social relationships than psychologists or sociologists because we cannot interview our subjects about their relationships with others, and we cannot rely on introspection for an understanding of what these relationships mean to them.
From page 126...
... The Structure and Function of Social Bonds Among Female Baboons in Amboseli We used the approach described above to assess the nature of social relationships among females. For each pair of females, we tabulated the proportion of observation time that they were nearest neighbors or grooming one another, and used these values to create a dyad-specific composite sociality index (DSI, Silk et al., 2006a)
From page 127...
... Preferred partners are typically close kin, but nearly all females seem to form a few close relationships even if no close kin are available. Replication: The Structure and Function of Social Bonds Among Female Baboons in Moremi After the Amboseli data were published, Dorothy Cheney and ­ obertR Seyfarth invited me to collaborate on analyses of social relationships among female baboons in the Moremi Reserve of the Okavango Delta of Botswana.
From page 128...
... . Finally, we investigated the adaptive consequences of close social bonds among the Moremi females using survivorship analysis methods.
From page 129...
... Like female baboons and male chimpanzees, the male Assamese macaques spent more time grooming and associating with some male partners than others. Schülke and his colleagues discovered that males that formed the strongest bonds were more likely to support one another in aggressive interactions.
From page 130...
... Coalitionary Support Male Assamese macaques that formed close social bonds also supported one another in coalitions. Males that participated in coalitions most often were most likely to rise in rank, and high-ranking males had priority of access to receptive females and achieved higher reproductive success than lower ranking males.
From page 131...
... (2012) investigated the impact of close social bonds on the frequency with which female chacma baboons in semi-arid habitats in Namibia fed together in a single food patch.
From page 132...
... In this section, I review evidence that suggests that social ties help animals cope with several major stressors, social isolation, social instability, and subordinate status. I also describe results from several studies that suggest that the structure of individuals' social networks is linked to stress levels.
From page 133...
... Those that entered new groups on their own had substantially higher cortisol levels after one week than those that were accompanied by a familiar peer. Instability in the male dominance hierarchy has direct effects on females in some species.
From page 134...
... However, females that lost a close relative experienced greater increases in fGC levels than individuals that were present in the group, but did not suffer a personal loss. Subordinate Status There is considerable discussion about the effects of dominance rank on stress levels, with some studies showing that high-ranking individuals have lower cortisol levels than low-ranking individuals, and others showing the opposite effect (Sapolsky, 2005)
From page 135...
... Social Networks Two studies have examined the impact of an individual's social networks on cortisol levels in primates. During a period of stability in the male dominance hierarchy, female baboons in Moremi had lower fGC months during months in which they concentrated their grooming on a small number of partners than in months in which they distributed their grooming more evenly among potential partners (Crockford et al., 2008)
From page 136...
... Griffin and Nunn's (2012) results suggest that the structure of individuals' social networks might matter, and several studies provide evidence that supports this idea.
From page 137...
... For group-living animals, including other primates, the ability to form and maintain close social bonds may create multiple direct benefits, including reduced vulnerability to predators, greater access to food resources, and protection from harassment. Moreover, social ties seem to help animals cope with various sources of social stress, perhaps because their relationships provide a greater sense of predictability and control, and this in turn affects health outcomes.
From page 138...
... Animal Behaviour, 86(5)
From page 139...
... . Social stressors and coping mechanisms in wild female baboons (Papio hamadryas ursinus)
From page 140...
... . Primate Social Relationships: An Integrated Approach.
From page 141...
... Male and female chacma baboons form friend ships based on likelihood of paternity. Animal Behaviour, 79(5)
From page 142...
... . Social relationships among adult female baboons (Papio cynocephalus)
From page 143...
... . The benefits of social capital: Close social bonds among female baboons enhance offspring survival.


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