Group-level cooperation in chimpanzees is shaped by strong social ties

Liran Samuni,Catherine Crockford,Roman M Wittig

doi:10.1038/s41467-020-20709-9

Abstract

Humans maintain extensive social ties of varying preferences, providing a range of opportunities for beneficial cooperative exchange that may promote collective action and our unique capacity for large-scale cooperation. Similarly, non-human animals maintain differentiated social relationships that promote dyadic cooperative exchange, but their link to cooperative collective action is little known. Here, we investigate the influence of social relationship properties on male and female chimpanzee participations in a costly form of group action, intergroup encounters. We find that intergroup encounter participation increases with a greater number of other participants as well as when participants are maternal kin or social bond partners, and that these effects are independent from one another and from the likelihood to associate with certain partners. Together, strong social relationships between kin and non-kin facilitate group-level cooperation in one of our closest living relatives, suggesting that social bonds may be integral to the evolution of cooperation in our own species.

Highlights

Humans maintain extensive social ties of varying preferences, providing a range of opportunities for beneficial cooperative exchange that may promote collective action and our unique capacity for large-scale cooperation
This hypothesis is supported by studies showing that chimpanzee males more often patrol the borders of their territory together with their maternal brothers compared to unrelated dyads[18] or with males with which they groom more[44], and that the presence of a kin or non-kin bond partner during chimpanzee intergroup encounters appears to buffer stress responses[4]
We find that cohesive engagement of many community members and the presence of adult maternal kin or social bond partners predict the likelihood of males and females to contribute to hostile encounters with rival groups

Summary

Introduction

Humans maintain extensive social ties of varying preferences, providing a range of opportunities for beneficial cooperative exchange that may promote collective action and our unique capacity for large-scale cooperation. It is reasonable to assume that such consistent social exchange that occurs within one’s group and aids in navigating within-group competitive interactions will predict coordination and coalitionary support during between-group competitive interactions[44], potentially facilitated by oxytocinergic system activity[45,46] This hypothesis is supported by studies showing that chimpanzee males more often patrol the borders of their territory together with their maternal brothers compared to unrelated dyads[18] or with males with which they groom more[44], and that the presence of a kin or non-kin bond partner during chimpanzee intergroup encounters appears to buffer stress responses[4]. We investigate this during intergroup encounters that were either initiated or involved an active approach behaviour by the in-group, as otherwise no voluntary participation was made

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Conclusion