Social evaluation and decision-making in nonhuman primates
by Marie Hirel
Date of Examination:2024-12-05
Date of issue:2025-03-25
Advisor:Dr. Stefanie Keupp
Referee:Dr. Stefanie Keupp
Referee:Prof. Dr. Hannes Rakoczy
Persistent Address:
http://dx.doi.org/10.53846/goediss-11165
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Abstract
English
One of the challenges of living in a group is constantly having to decide when, how, and whom to interact with among several conspecifics in plenty of different contexts. For optimal decision-making, social animals can benefit from acquiring social information about others to selectively choose the most optimal partners to interact with. Accumulating research evidence that nonhuman primates form social knowledge and adapt their behaviours towards conspecifics that can benefit them. For example, individuals prefer interacting with the most cooperative and helpful group members, or the most competent at foraging tasks. Yet, how nonhuman primates acquire and use social information about others remains unclear. Their behaviours can be explained by an outcome-based process, associative learning strategies from past interactions, or by social evaluation inferences, impression formation about others from their past behaviours. In this thesis, I investigate whether nonhuman primates evaluate others’ characteristics and use their impressions to select social partners strategically. Three studies using different experimental settings were conducted on captive groups of Tonkean macaques (Macaca tonkeana) and brown capuchins (Sapajus apella) at the Centre de Primatologie – Silabe de l’Université de Strasbourg, in France. Both species live in multi-male, multi-female tolerant groups and have demonstrated selective partner choices, social knowledge, and cognitive skills. I first investigated whether Tonkean macaques and brown capuchins can evaluate the skilfulness of others and use their evaluation to select the optimal partner in two different contexts. In the first experiment, the subjects observed two human actors (skilful vs unskilled) trying to open several containers to release food. Afterward, Tonkean macaques and brown capuchins did not choose the skilful actor more frequently than the unskilled one to manipulate a food container. However, when their initial preferences for the actors were considered, the subjects successfully shifted their preference for the skilful actor – the better option to maximise reward outcomes. They did not learn to choose the skilful actor through direct experience during the test session nor did they base their decisions on the outcome they experienced in previous trials. Subjects also decreased their time looking at the unskilled actor after the demonstrations. Therefore, Tonkean macaques and brown capuchins used information about the actors’ skills to adapt their behaviours for optimising their food intake. Yet, as subjects experienced a differential reward after the actors’ demonstrations, an outcome-based process underlying their behaviours during the test cannot be ruled out. In contrast, for the second experiment, Tonkean macaques only observed two human actors (skilful vs unskilled) operating a puzzle task without obtaining food after the actors’ demonstrations. I then measured their probability of choosing the skilful actor – the optimal choice – to cooperate in a co-action version of the puzzle tasks. Tonkean macaques did not prefer to cooperate with the skilful over the unskilled partner. They did not spontaneously use information about the actors’ skills acquired by observation, nor did they learn through trials to use information from direct experience with the partners. Although recruiting a partner in a cooperative context might be more complex than the testing conditions in the first study, these results indicate that Tonkean macaques did not adapt their behaviours when direct experience with the partners during the demonstration phase was no longer possible. In a third experiment, I investigate whether Tonkean macaques can evaluate and prefer social agents that help rather than hinder others. For comparative purposes, I used a paradigm widely used to study children’s preference for helpers: the hill paradigm. Bonobos tested with the hill paradigm preferred hinderers over helper agents, contrasting previous findings on other nonhuman primates. Tonkean macaques watched several times videos in which an animated helper agent pushed a climber up a hill while an animated hinderer agent pushed the climber down the hill. No food was involved in the interactions between the animated agents, nor obtained by the subjects after the agents’ actions. Afterward, Tonkean macaques did not prefer the helper over the hinderer (or vice versa). No potential effects of perceptual features of the animated agents (shape, colour, movement) were found. While Tonkean macaques and bonobos share some behavioural and social characteristics, they do not show the same pattern of choices. Yet, the low level of attention of the subjects to the videos indicates a lack of interest in the experimental stimuli, raising a potential limitation of using videos and animated agents for testing this species. In conclusion, Tonkean macaques and brown capuchins used social information about the actors’ skills to inform their decisions, which supports previous findings that nonhuman primates can assess others’ competence. The results of the third study are however inconclusive to evidence an assessment of others’ prosocial tendencies in Tonkean macaques, in contrast to previous findings on other primate species. In addition, the findings do not evidence social reasoning skills corresponding to social evaluation inferences in these species and rather suggest that an outcome-based process underlies social information acquisition and decision-making in nonhuman primates. Yet, the inter-individual variation combined with the small sample sizes and potential methodological limitations found in this thesis call for further investigation of social evaluation in primates. Importantly, future studies using various experimental paradigms reflecting the species’ socio-ecological conditions are needed to better understand in which contexts evaluating and considering others’ competence or prosocial tendencies is valuable for each species.
Keywords: social cognition; Tonkean macaques; Macaca tonkeana; impression formation; partner choice; competence; skill attribution; cooperation; prosocial preference; brown capuchins; Sapajus apella; social evaluation; decision-making; primates; third-party observation; animated social agent; co-action task; social knowledge
