Abstract
Social relationships endow health and fitness benefits, but considerable variation exists in the extent to which individuals form and maintain salutary social relationships. The mental and physical health effects of social bonds are more strongly related to perceived isolation (loneliness) than to objective social network characteristics. We sought to develop an animal model to facilitate the experimental analysis of the development of, and the behavioral and biological consequences of, loneliness. In Study 1, using a population-based sample of older adults, we examined how loneliness was influenced both by social network size and by the extent to which individuals believed that their daily social interactions reflected their own choice. Results revealed three distinct clusters of individuals: (i) individuals with large networks who believed they had high choice were lowest in loneliness, (ii) individuals with small social networks who believed they had low choice were highest in loneliness, and (iii) the remaining two groups were intermediate and equivalent in loneliness. In Study 2, a similar three-group structure was identified in two separate samples of adult male rhesus monkeys (Macaca mulatta) living in large social groups: (i) those high in sociability who had complex social interaction with a broad range of social partners (putatively low in loneliness), (ii) those low in sociability who showed tentative interactions with certain classes of social partners (putatively high in loneliness), and (iii) those low in sociability who interacted overall at low levels with a broad range of social partners (putatively low or intermediate in loneliness). This taxonomy in monkeys was validated in subsequent experimental social probe studies. These results suggest that, in highly social nonhuman primate species, some animals may show a mismatch between social interest and social attainment that could serve as a useful animal model for experimental and mechanistic studies of loneliness.
Highlights
For social species, having and maintaining social relationships with conspecifics is critical to individual survival and well-being
We investigated the extent to which similar groupings were evident in monkeys (Study 2) and whether their behavior in response to social probes paralleled the differences that have been found among people who differ in their level of loneliness (Study 3)
For Sample 1, the 31 LS animals were distributed in two groups, designated Manifestly Low Sociable (MLS; n = 5) and Truly Low Sociable (TLS; n = 26); group membership was unrelated to Sociability (p = .44), age (p = .97), or rank (p = .31)
Summary
For social species, having and maintaining social relationships with conspecifics is critical to individual survival and well-being. Considerable variation exists, in the extent to which individuals form and maintain salutary social relationships [9] These variations have often been analyzed in terms of broad personality traits, such as introversion. Whether experimentally induced or naturally occurring, cause people to feel unhappy and unsafe, heightening their sensitivity to perceived social threats and attacks, and leading them to behave in a self-protective, overly reactive fashion [10]. Many of these effects can be found in experimental studies of isolation in nonhuman social animals, as well [3]
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