On the evolution of baboon greeting rituals

Social uncertainty promotes signal complexity during approaches in wild chimpanzees (Pan troglodytes verus) and mangabeys (Cercocebus atys atys)

The social complexity hypothesis for the evolution of communication posits that complex social environments require greater communication complexity for individuals to effectively manage their relationships. We examined how different socially uncertain contexts, reflecting an increased level of social complexity, relate to variation in signalling within and between two species, which display varying levels of fission-fusion dynamics (sympatric-living chimpanzees and sooty mangabeys, Taï National Park, Ivory Coast). Combined signalling may improve message efficacy, notably when involving different perception channels, thus may increase in moments of high social uncertainty. We examined the probability of individuals to emit no signal, single or multisensory or combined (complex) signals, during social approaches which resulted in non-agonistic outcomes. In both species, individuals were more likely to use more combined and multisensory signals in post-conflict approaches with an opponent than in other contexts. The clearest impact of social uncertainty on signalling complexity was observed during chimpanzee fusions, where the likelihood of using complex signals tripled relative to other contexts. Overall, chimpanzees used more multisensory signals than mangabeys. Social uncertainty may shape detected species differences in variation in signalling complexity, thereby supporting the hypothesis that social complexity, particularly associated with high fission-fusion dynamics, promotes signalling complexity.

Adult play and the evolution of tolerant and cooperative societies

Play is generally considered an immature affair. However, adult play is present in several mammal species living in complex social systems. Here, I hypothesize that adult social play is favored by natural selection in those species characterized by high level of social tolerance and/or by the need of others' cooperation to reach a goal (i.e., leverage). The integration and comparison of bio-behavioral data on non-human primates and wild social carnivores allows drawing a comprehensive picture on the importance of adult play in facing unpredictable, novel social situations and in overcoming stressful experiences. The ability to cope with potentially competitive interactions through play can favor the emergence of egalitarian societies. A further interesting and beneficial aspect of adult play is its role in synchronizing group activities and favoring collective decision making by renovating the motivation to cooperate in groupmates. As a last step, some considerations about the presence of adult play in the most egalitarian and cooperative human groups (e.g., hunter-gatherer societies) allows discussing the apparent dichotomy between cultural and biological evolution of certain behavioral traits, including social play in adulthood.

Baboon perspectives on the ecology and behavior of early human ancestors

For more than 70 y researchers have looked to baboons (monkeys of the genus Papio ) as a source of hypotheses about the ecology and behavior of early hominins (early human ancestors and their close relatives). This approach has undergone a resurgence in the last decade as a result of rapidly increasing knowledge from experimental and field studies of baboons and from archeological and paleontological studies of hominins. The result is a rich array of analogies, scenarios, and other stimuli to thought about the ecology and behavior of early hominins. The main intent here is to illustrate baboon perspectives on early hominins, with emphasis on recent developments. This begins with a discussion of baboons and hominins as we know them currently and explains the reasons for drawing comparisons between them. These include occupation of diverse environments, combination of arboreal and terrestrial capabilities, relatively large body size, and sexual dimorphism. The remainder of the paper illustrates the main points with a small number of examples drawn from diverse areas of interest: diet (grasses and fish), danger (leopards and crocodiles), social organization (troops and multilevel societies), social relationships (male–male, male–female, female–female), communication (possible foundations of language), cognition (use of social information, comparison of self to others), and bipedalism (a speculative developmental hypothesis about the neurological basis). The conclusion is optimistic about the future of baboon perspectives on early hominins.

Yet Another Non-Unique Human Behaviour: Leave-Taking in Wild Chacma Baboons (Papio ursinus)

Simple Summary

Although greeting is well-studied across animal species, its counterpart, leave taking, is little studied in nonhumans. Here, we review the previous limitations of leave-taking research and use this to develop a new method for studying leave taking in nonhumans. Using videos of chacma baboons in Gorongosa National Park, Mozambique, we compared behaviours at the end of social departures to nonsocial departures. We found that shifting orientation towards the direction of parting was significantly more likely in social departures compared to nonsocial departures. As the first evidence of leave taking in a wild nonhuman species, we suggest that leave taking is not uniquely human as previously argued, and that our method could be used to further explore the presence of leave taking in other nonhuman species.

Abstract

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.

Variation in communicative complexity in relation to social structure and organization in non-human primates

Communicative complexity relates to social complexity, as individuals in more complex social systems either use more signals or more complex signals than individuals living in less complex ones. Taking the individual group member's perspective, here we examine communicative complexity in relation to social complexity, which arises from two components of social systems: social structure and social organization. We review the concepts of social relationships and social complexity and evaluate their implications for communicative and cognitive complexity using examples from primate species. We focus on spider monkeys (Ateles geoffroyi), as their social organization is characterized by flexibility in grouping dynamics and they use a variety of communicative signals. We conclude that no simple relationship exists among social complexity, communicative complexity and cognitive complexity, with social complexity not necessarily implying cognitive complexity, and communicative and cognitive complexity being independently linked to social complexity. To better understand the commonly implied link between social complexity and cognitive complexity it is crucial to recognize the complementary role of communicative complexity. A more elaborated communicative toolkit provides the needed flexibility to deal with dynamic and multifaceted social relationships and high variation in fission-fusion dynamics. This article is part of the theme issue 'Cognition, communication and social bonds in primates'.

Sequence organization and embodied mutual orientations: openings of social interactions between baboons

Human interactions are organized in sequence, which is a key component of Levinson's 'interaction engine.' Referring back to the field where it originated, conversation analysis, we discuss its relevance within the interaction engine, before moving on to show how sequence organization is actually oriented to not only humans in social interaction, but also to non-human animals. On the basis of video-recorded encounters between baboons (Papio anubis), we study canonical sequences constituting openings and, within them, greetings. Openings are the locus where future interactants adjust to each other to coordinately enter in interaction, thus achieving a common definition of their context, activity, and relationships. The analysis shows that the ways individuals spatially approach each other provide systematic interactional affordances for how the first sequences of actions in the opening are formatted, initiated, and responded to. Adopting sequential multimodal analysis, we demonstrate how participants orient to central features of sequence organization-its sequential implicativeness and the expectations it produces-building on them their interpretations of others' actions, their responsivity, and their mutual understanding of the ongoing course of action as it unfolds. This paves the way for further reflections on the pervasiveness of the interactional engine in human and non-human primate communication. This article is part of the theme issue 'Revisiting the human 'interaction engine': comparative approaches to social action coordination'.

Ritual explained: interdisciplinary answers to Tinbergen's four questions

Convergent developments across social scientific disciplines provide evidence that rituals are a psychologically prepared and culturally inherited behavioural hallmark of our species. The dramatic diversity of ritual practices ranges from simple greetings to elaborate religious ceremonies, from the benign to life-threatening. Yet our scientific understanding of this core human trait remains limited. Explaining the universality, functionality and diversity of ritual requires insight from multiple disciplines. This special issue integrates research from anthropology, archaeology, biology, primatology, cognitive science, psychology, religious studies and demography to build an interdisciplinary account of ritual. The objective is to contribute to an integrative explanation of ritual by addressing Tinbergen's four key questions. These include answering ultimate questions about the (i) phylogeny and (ii) adaptive functions of ritual; and proximate questions about the (iii) mechanisms and (iv) ontogeny of ritual. The intersection of these four complementary lines of inquiry yields new avenues for theory and research into this fundamental aspect of the human condition, and in so doing, into the coevolution of cognition and culture. This article is part of the theme issue 'Ritual renaissance: new insights into the most human of behaviours'.