Bystanders, parcelling, and an absence of trust in the grooming interactions of wild male chimpanzees

Stefano S K Kaburu,Nicholas E Newton-Fisher

doi:10.1038/srep20634

Stefano S K Kaburu, Nicholas E Newton-Fisher

Open Access

https://doi.org/10.1038/srep20634

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Abstract

The evolution of cooperation remains a central issue in socio-biology with the fundamental problem of how individuals minimize the risks of being short-changed (‘cheated’) should their behavioural investment in another not be returned. Economic decisions that individuals make during interactions may depend upon the presence of potential partners nearby, which offers co operators a temptation to defect from the current partner. The parcelling model posits that donors subdivide services into parcels to force cooperation, and that this is contingent on opportunities for defection; that is, the presence of bystanders. Here we test this model and the effect of bystander presence using grooming interactions of wild chimpanzees. We found that with more bystanders, initiators gave less grooming at the beginning of the bout and were more likely to abandon a grooming bout, while bouts were less likely to be reciprocated. We also found that the groomer’s initial investment was not higher among frequent groomers or stronger reciprocators, suggesting that contrary to current assumptions, grooming decisions are not based on trust, or bonds, within dyads. Our work highlights the importance of considering immediate social context and the influence of bystanders for understanding the evolution of the behavioural strategies that produce cooperation.

Highlights

Economic decisions that individuals make during interactions may depend upon the presence of potential partners nearby which o ers co operators a temptation to defect from the current partner
Economic decisions that individuals make when interacting with group members may well depend upon the presence of potential partners nearby, and it is vital to determine the extent to which individuals respond to bystander presence10,11. he importance of bystanders is highlighted in two particular theoretical approaches, Noë and colleagues’[10,11] biological markets theory (BMT) and Connor’s parcelling model[12,13] for the evolution of cooperative exchanges
4% of grooming bouts were interrupted; this was less likely to occur with more male bystanders (GLMM: β ± SE = −0.418 ± 0.174, t = −2.40, p = 0.02), the number of male bystanders did not depend on the context during which the grooming interaction occurred (GLMM: β ± SE = −0.02 ± 0.062, t = −0.39, p = 0.69)

Summary

Introduction

The evolution of cooperation remains a central issue in socio-biology with the fundamental problem of how individuals minimize the risks of being short-changed (‘cheated’) should their behavioural investment in another not be returned. Understanding the evolution of cooperation in social animals remains a central issue in socio-biology[8,9], with the fundamental problem of how individuals minimize the risks of being short-changed (‘cheated’) should their behavioural investment in another not be returned. Central to Connor’s model is the concept that the existence of bystanders generates a temptation to defect from the current partner, and that this drives the parcelling (subdividing) of a social interaction such. RTS is not so much concerned with partner control (forcing a partner into a cooperative interaction) but with reserving signiicant cooperative investment for social partners who demonstrate a willingness to do likewise.

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