Leave-taking behaviours habitually occur before separation from social interaction in most human societies. It is thought to be a human universal, providing ritual brackets around interaction. Despite Knapp’s claim that leave-taking can tell us a good deal about human interaction, the topic remains critically overlooked from an evolutionary perspective. Cross-species data on leave-taking would be key to unveiling its evolutionary history and its role in sociality, but studies focusing on non-human species are rare. Here, leave-taking is reviewed using an evolutionary approach, pitting it against its symmetrical counterpart, greeting, and emphasising the lacunae in research on leave-taking. It is argued that leave-taking is overdue for serious, empirical attention regarding the ways in which leave-taking could contribute to understanding social evolution. Finally, methods are outlined to operationalise the study of leave-taking and propose the use of “levels of separation” to allow comparison of human and non-human species and to expand research efforts.

Leave taking is a common, possibly universal, feature of human social behaviour that has undergone very little empirical research. Although the importance remains unknown, it has been suggested to play an important role in managing separations, mitigating the risk, and increasing social bonding beyond the interaction itself. In nonhuman species, the literature is virtually absent, but identifying leave taking beyond humans may provide unique insights into the evolutionary history of this behaviour and shed light onto its proximate and ultimate function(s). Methods to study leave taking are not well-established, and the variation in definitions, measures, and control variables presented in past studies poses additional challenges. Baboons are a valuable model for investigating human behavioural evolution: as a flexible, highly adaptable, and social primate whose radiation is, similarly to humans, associated with the emergence of the African savannah biome. Using the framework and definition proposed by Baehren, we investigated the presence of leave taking in a wild, generalist primate and tested a range of candidate behaviours on prerecorded video footage: (1) self-scratching, (2) eye gaze, and (3) orientation in the direction of parting. Using multivariate analysis, controlling for interaction duration and individual variation, our results show that orientation in the direction of parting occurs predominantly before social separation events. These results indicate evidence of leave taking in a wild nonhuman population and contrast with previous ideas that this is a uniquely human behaviour. The presence of leave taking in baboons suggests a deep evolutionary history of this behaviour, warranting further investigation into its function and presence across other nonhuman primate species.

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