Chimpanzees act cooperatively in the wild, but whether they afford benefits to others, and whether their tendency to act prosocially varies across communities, is unclear. Here, we show that chimpanzees from neighboring communities provide valuable resources to group members at personal cost, and that the magnitude of their prosocial behavior is group specific. Provided with a resource-donation experiment allowing free (partner) choice, we observed an increase in prosocial acts across the study period in most of the chimpanzees. When group members could profit (test condition), chimpanzees provided resources more frequently and for longer durations than when their acts produced inaccessible resources (control condition). Strikingly, chimpanzees’ prosocial behavior was group specific, with more socially tolerant groups acting more prosocially. We conclude that chimpanzees may purposely behave prosocially toward group members, and that the notion of group-specific sociality in nonhuman animals should crucially inform discussions on the evolution of prosocial behavior.

Intergroup variation (IGV) refers to variation between different groups of the same species. While its existence in the behavioural realm has been expected and evidenced, the potential effects of IGV are rarely considered in studies that aim to shed light on the evolutionary origins of human socio-cognition, especially in our closest living relatives—the great apes. Here, by taking chimpanzees as a point of reference, we argue that (i) IGV could plausibly explain inconsistent research findings across numerous topics of inquiry (experimental/behavioural studies on chimpanzees), (ii) understanding the evolutionary origins of behaviour requires an accurate assessment of species' modes of behaving across different socio-ecological contexts, which necessitates a reliable estimation of variation across intraspecific groups, and (iii) IGV in the behavioural realm is increasingly likely to be expected owing to the progressive identification of non-human animal cultures. With these points, and by extrapolating from chimpanzees to generic guidelines, we aim to encourage researchers to explicitly consider IGV as an explanatory variable in future studies attempting to understand the socio-cognitive and evolutionary determinants of behaviour in group-living animals.

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Animals need to adjust their decision-making strategies to the ecological challenges of their environment. Variation in ecological unpredictability and harshness thus seem to affect their decisions in the wild. In our study, we combine methods from human life history theory and previous comparative work with chimpanzees to investigate whether current variability in ecological factors such as reward unpredictability and harshness affect chimpanzees’ decision-making strategies in two value-based scenarios. We presented chimpanzees with choices varying in the probability of obtaining food rewards (risk-choice task) and in their temporal availability (temporal discounting task). These scenarios were preceded by different sets of priming phases mimicking variability in resource unpredictability (predictable or unpredictable rewards) and harshness (abundant or scarce rewards). In addition, we implemented a social manipulation to explore whether variations in unpredictable gains and losses affected chimpanzees’ performance in both tasks. We found that chimpanzees were only affected by the social manipulation in the risk-choice scenario. Specifically, after a period of constant food losses chimpanzees became less risk prone. We discuss how different types of negative experiences affect chimpanzees’ decisions.