Abstract
Complex societies are shaped by social relationships between multiple individuals. The pressure to track these relationships has driven the evolution of social cognition in primates. Importantly, it can be adaptive to track not only personal relationships, but also those established between third-parties. Primates have knowledge about others’ dominance hierarchies and kinship, but we do not know to what extent they also understand friendships. In a playback experiment, Tonkean macaques were presented with simulated conflicts involving third-party female dyads who were established friends or non-friends. Hearing a conflict between friends elicited a stronger behavioural response in listeners (i.e. an increase in looking time) compared to hearing a conflict between non-friends. Conflicts between friends are likely to represent a greater disruption of the social group and structure of the network, and therefore this difference in response may represent an adaptive strategy employed by the macaques to selectively monitor important social interactions in the group. These findings provide evidence that Tonkean macaques (and potentially other primates) can classify the relationships of others based on their degree of friendship and additionally, confirms the important role friendships have within the societies of social primates.
Highlights
Complex societies are shaped by social relationships between multiple individuals
The adaptive value of social relationships in maintaining stable and cohesive social groups has driven the evolution of social knowledge in primates[4], and has allowed for a cognitive capacity that enables primates to retain information about the relationships they have previously established with others[5]
The Tonkean macaque represents an ideal candidate for this study here, as we may expect any selective pressures driving the ability to understand third-party friendships to be exaggerated in this species
Summary
Complex societies are shaped by social relationships between multiple individuals. The pressure to track these relationships has driven the evolution of social cognition in primates. The adaptive value of social relationships in maintaining stable and cohesive social groups has driven the evolution of social knowledge in primates[4], and has allowed for a cognitive capacity that enables primates (and many non-primates) to retain information about the relationships they have previously established with others[5] This ability has been evidenced in numerous observational and playback experiments[6], where monkeys have been shown to look preferentially and respond adaptively to the social stimuli of their kin[7], friends[8] or more dominant individuals[9]. The Tonkean macaque represents an ideal candidate for this study here, as we may expect any selective pressures driving the ability to understand third-party friendships to be exaggerated in this species
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