Conservatism and “copy-if-better” in chimpanzees (Pan troglodytes)

This work was funded by the project SOMICS, ERC-Synergy grant # 609819 to Josep Call.Social learning is predicted to evolve in socially living animals provided the learning process is not random but biased by certain socio-ecological factors. One bias of particular interest for the emergence of (cumulative) culture is the tendency to forgo personal behaviour in favour of relatively better variants observed in others, also known as the "copy-if-better" strategy. We investigated whether chimpanzees employ copy-if-better in a simple token-exchange paradigm controlling for individual and random social learning. After being trained on one token-type, subjects were confronted with a conspecific demonstrator who either received the same food reward as the subject (control condition) or a higher value food reward than the subject (test condition) for exchanging another token-type. In general, the chimpanzees persisted in exchanging the token-type they were trained on individually, indicating a form of conservatism consistent with previous studies. However, the chimpanzees were more inclined to copy the demonstrator in the test compared to the control condition, indicating a tendency to employ a copy-if-better strategy. We discuss our findings in light of their relevance to the emergence of cumulative culture.Publisher PDFPeer reviewe

Biased cultural transmission of a social custom in chimpanzees

Cultural transmission studies in animals have predominantly focused on identifying between-group variation in tool-use techniques, while immaterial cultures remain understudied despite their potential for highlighting similarities between human and animal culture. Here, using long-term data from two chimpanzee communities, we tested whether one of chimpanzees' most enigmatic social customs-the grooming handclasp-is culturally transmitted by investigating the influence of well-documented human transmission biases on their variational preferences. After identifying differences in style preferences between the communities, we show that older and dominant individuals exert more influence over their partners' handclasp styles. Mothers were equally likely to influence their offspring's preferences as nonkin, indicating that styles are transmitted both vertically and obliquely. Last, individuals gradually converged on the group style, suggesting that conformity guides chimpanzees' handclasp preferences. Our findings show that chimpanzees' social lives are influenced by cultural transmission biases that hitherto were thought to be uniquely human

Food sharing with friends and acquaintances:A study in preschool boys and girls

IntroductionThe current study examined whether preschoolers in a (semi-)natural situation shared more food with friends or acquaintances, and whether this was different between boys and girls, older and younger children, and for preferred and non- preferred food. In order to do so, we replicated and extended the classical work of Birch and Billman in a Dutch sample.MethodsParticipants included 91 children aged between 3 to 6 years (52.7% boys, 93.4% Western European) from a middle- to upper-middle-class neighborhood in the Netherlands.ResultsThe results revealed that children shared more non-preferred than preferred food with others. Girls gave more non-preferred food to acquaintances than to friends, whereas boys gave more to friends than to acquaintances. No effect of relationship was found for preferred food. Older children shared more food than younger children. Compared to acquaintances, friends made more active attempts to get food. Moreover, children who were not shared with were just as likely to share food as children who were shared with.DiscussionOverall, only a small degree of agreement with the original study was found: Some significant findings could not be replicated, and some unconfirmed hypotheses of the original study were supported. The results underscore both the need for replications and studying the effect of social-contextual factors in natural settings

Tool use for corpse cleaning in chimpanzees

For the first time, chimpanzees have been observed using tools to clean the corpse of a deceased group member. A female chimpanzee sat down at the dead body of a young male, selected a firm stem of grass, and started to intently remove debris from his teeth. This report contributes novel behaviour to the chimpanzee’s ethogram, and highlights how crucial information for reconstructing the evolutionary origins of human mortuary practices may be missed by refraining from developing adequate observation techniques to capture non-human animals’ death responses.Publisher PDFPeer reviewe

Chimpanzees use social information to acquire a skill they fail to innovate

E.J.C.v.L. was funded by the European Union under European Research Council Starting Grant no. 101042961—CULT_ORIGINS.Cumulative cultural evolution has been claimed to be a uniquely human phenomenon pivotal to the biological success of our species. One plausible condition for cumulative cultural evolution to emerge is individuals’ ability to use social learning to acquire know-how that they cannot easily innovate by themselves. It has been suggested that chimpanzees may be capable of such know-how social learning, but this assertion remains largely untested. Here we show that chimpanzees use social learning to acquire a skill that they failed to independently innovate. By teaching chimpanzees how to solve a sequential task (one chimpanzee in each of the two tested groups, n = 66) and using network-based diffusion analysis, we found that 14 naive chimpanzees learned to operate a puzzle box that they failed to operate during the preceding three months of exposure to all necessary materials. In conjunction, we present evidence for the hypothesis that social learning in chimpanzees is necessary and sufficient to acquire a new, complex skill after the initial innovation.Peer reviewe

Chimpanzee communities differ in their inter- and intrasexual social relationships

Male and female human social bonding strategies are culturally shaped, in addition to being genetically rooted. Investigating nonhuman primate bonding strategies across sex groups allows researchers to assess whether, as with humans, they are shaped by the social environment or whether they are genetically predisposed. Studies of wild chimpanzees show that in some communities males have strong bonds with other males, whereas in others, females form particularly strong intrasex bonds, potentially indicative of cultural differences across populations. However, excluding genetic or ecological explanations when comparing different wild populations is difficult. Here, we applied social network analysis to examine male and female social bonds in two neighbouring semiwild chimpanzee groups of comparable ecological conditions and subspecies compositions, but that differ in demographic makeup. Results showed differences in bonding strategies across the two groups. While female–female party co-residence patterns were significantly stronger in Group 1 (which had an even distribution of males and females) than in Group 2 (which had a higher proportion of females than males), there were no such differences for male–male or male–female associations. Conversely, female–female grooming bonds were stronger in Group 2 than in Group 1. We also found that, in line with captive studies but contrasting research with wild chimpanzees, maternal kinship strongly predicted proximity and grooming patterns across the groups. Our findings suggest that, as with humans, male and female chimpanzee social bonds are influenced by the specific social group they live in, rather than predisposed sex-based bonding strategies. Graphical Abstract: [Figure not available: see fulltext.

Early Trauma Leaves No Social Signature in Sanctuary-Housed Chimpanzees (Pan troglodytes)

Negative early experiences can have detrimental effects on social functioning in later life, both in humans as well as in other socially-living animals. In zoo-housed chimpanzees, recent evidence suggests that there may be a lingering signature of early trauma on individuals' social interaction tendencies as measured by social proximity and grooming. Here, we address whether a similar effect would be observable in chimpanzees living under semi-wild conditions in an African sanctuary. By analysing party size, close proximity and social grooming, we show that in this specific sanctuary, chimpanzees that suffered early trauma (n = 42) were socially indistinguishable from chimpanzees who were born and raised by their mothers in the sanctuary (n = 36). Our findings indicate that chimpanzees may not be irreversibly affected by early social trauma, possibly owing to rehabilitation in stable social groups in a semi-natural environment. Beyond identifying sanctuaries as valuable rehabilitation centres for orphaned chimpanzees, this study demonstrates a remarkable social flexibility in one of our closest living relatives

Chimpanzees behave prosocially in a group-specific manner

Funding: EJCvL was funded by a Postdoctoral Fellowship awarded by the Research Foundation Flanders (FWO) and an ERC-Synergy Grant (no. 609819) awarded to JC.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.Publisher PDFPeer reviewe

Adult bonobos show no prosociality in both prosocial choice task and group service paradigm

Previous studies reported contrasting conclusions concerning bonobo prosociality, which are likely due to differences in the experimental design, the social dynamics among subjects and characteristics of the subjects themselves. Two hypotheses have been proposed to explain the occurrence of prosociality in animals: the cooperative breeding hypothesis and the self-domestication hypothesis. While the former predicts low levels of prosociality in bonobos because they are non-cooperative breeders, the latter predicts high levels of prosociality because self-domestication has been proposed to select for high levels of tolerance in this species. Here, we presented a group of thirteen bonobos with two platform food-provisioning tasks: the prosocial choice task (PCT) and the group service paradigm (GSP). The latter has so far never been applied to bonobos. To allow for free choice of participation and partner, we implemented both tasks in a group setting. Like in previous PCT studies, bonobos did not choose the prosocial option more often when a group member could benefit vs not benefit. In the GSP, where food provisioning is costly, only subadult bonobos showed a limited amount of food provisioning, which was much lower than what was previously reported for chimpanzees. In both experiments, adult subjects were highly motivated to obtain rewards for themselves, suggesting that bonobos behaved indifferently to the gains of group members. We suggest that previous positive food-provisioning prosociality results in bonobos are mainly driven by the behaviour of subadult subjects. The lack of prosociality in this study corresponds to the hypothesis that proactive food provisioning co-occurs with cooperative breeding and suggests that proactive prosociality might not be part of the self-domestication syndrome in bonobos

Food sharing with friends and acquaintances: A study in preschool boys and girls

INTRODUCTION: The current study examined whether preschoolers in a (semi-)natural situation shared more food with friends or acquaintances, and whether this was different between boys and girls, older and younger children, and for preferred and non- preferred food. In order to do so, we replicated and extended the classical work of Birch and Billman in a Dutch sample. METHODS: Participants included 91 children aged between 3 to 6 years (52.7% boys, 93.4% Western European) from a middle- to upper-middle-class neighborhood in the Netherlands. RESULTS: The results revealed that children shared more non-preferred than preferred food with others. Girls gave more non-preferred food to acquaintances than to friends, whereas boys gave more to friends than to acquaintances. No effect of relationship was found for preferred food. Older children shared more food than younger children. Compared to acquaintances, friends made more active attempts to get food. Moreover, children who were not shared with were just as likely to share food as children who were shared with. DISCUSSION: Overall, only a small degree of agreement with the original study was found: Some significant findings could not be replicated, and some unconfirmed hypotheses of the original study were supported. The results underscore both the need for replications and studying the effect of social-contextual factors in natural settings