Persistent social isolation reflects identity and social context but not maternal effects or early environment

Abstract

Individuals who are well integrated into society have greater access to resources and tend to live longer. Why some individuals are socially isolated and others are not is therefore puzzling from an evolutionary perspective. Answering this question requires establishing the mix of intrinsic and contextual factors that contribute to social isolation. Using social network data spanning up to half of the median adult lifespan in a gregarious primate, we found that some measures of social isolation were modestly repeatable within individuals, consistent with a trait. By contrast, social isolation was not explained by the identity of an animal’s mother or the group into which it was born. Nevertheless, age, sex and social status each played a role, as did kin dynamics and familiarity. Females with fewer close relatives were more isolated, and the more time males spent in a new group the less isolated they became, independent of their social status. These results show that social isolation results from a combination of intrinsic and environmental factors. From an evolutionary perspective, these findings suggest that social isolation could be adaptive in some contexts and partly maintained by selection.

Evolutionary Consequences of Social Isolation

“…Consistent with this, specific genetic mutations in a mouse model have been linked to variation in sensitivity to social isolation [23]. Combined with findings from Rhesus macaques that the tendency to experience social isolation is variable and repeatable in a more naturalistic setting [3], and field crickets (Teleogryllus oceanicus) which show crossing reaction norms for mate discrimination after experiencing social versus asocial rearing conditions [48], gene-by-social environment interactions coupled with the release of cryptic genetic variation suggests a plausible mechanism driving evolutionary consequences of social isolation, and a promising avenue for future research.…”

“…Nearly every animal has the potential to experience social isolation. Many studies examining its effects understandably focus on social species, such as humans [2], other primates [3], and eusocial arthropods [4], and the study of social isolation has gained most traction in human research in which a well-developed literature focuses on the sociological, psychological and medical significance of experiencing separation from others. Despite this, the experience of social isolation is also highly relevant in species that are classified as asocial [5].…”

Long-term repeatability in social behaviours suggests stable social phenotypes in wild chimpanzees

“…Importantly, we found consistent individual differences in multiple forms of social interaction. Much research to date on social phenotypes has focused solely on association patterns (19,25), or on single forms of dyadic interaction (20, 34), with a minority of studies examining consistency in multiple forms of social behaviours (89,98,99). Our study shows that consistent individual differences in social behaviour extends to patterns of aggression and affiliation, both of which should influence fitness more than association alone (43,44,85–88,100).…”

“…Alternatively, consistent between-individual differences in behaviour and sociality may arise due to behavioural tendencies associated with specific life history stages or dominance positions, which appear to be individual phenotypes because the data collection protocol does not extend across the lifespan of the species (34–36). Indeed, within the human literature, longitudinal studies suggest human behavioural tendencies and personality may be more labile than previously thought, with shifts in these tendencies predicted by a combination of age-related change or adjustment to particular life events, e.g.…”

“…The majority of non-human animal (hereafter animal) studies examining the repeatability of social behaviour have used comparatively short-term datasets, representing a limited period within the lifespan of the study species (34). In our study, we examine how social behaviours vary between individuals in wild, adult chimpanzees, utilising a behavioural dataset spanning over 20 years and more than 7500 full-day focal follows.…”