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Social norm complexity and past reputations in the evolution of cooperation

Nature volume 555, pages 242245 (08 March 2018) | Download Citation

Abstract

Indirect reciprocity is the most elaborate and cognitively demanding1 of all known cooperation mechanisms2, and is the most specifically human1,3 because it involves reputation and status. By helping someone, individuals may increase their reputation, which may change the predisposition of others to help them in future. The revision of an individual’s reputation depends on the social norms that establish what characterizes a good or bad action and thus provide a basis for morality3. Norms based on indirect reciprocity are often sufficiently complex that an individual’s ability to follow subjective rules becomes important4,5,6, even in models that disregard the past reputations of individuals, and reduce reputations to either ‘good’ or ‘bad’ and actions to binary decisions7,8. Here we include past reputations in such a model and identify the key pattern in the associated norms that promotes cooperation. Of the norms that comply with this pattern, the one that leads to maximal cooperation (greater than 90 per cent) with minimum complexity does not discriminate on the basis of past reputation; the relative performance of this norm is particularly evident when we consider a ‘complexity cost’ in the decision process. This combination of high cooperation and low complexity suggests that simple moral principles can elicit cooperation even in complex environments.

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Acknowledgements

This work was supported by Fundação para a Ciência e Tecnologia (FCT) through grants SFRH/BD/94736/2013, PTDC/EEI-SII/5081/2014, PTDC/MAT/STA/3358/2014, UID/BIA/04050/2013 and UID/CEC/50021/2013. We are grateful to A. P. Francisco and M. Janota for comments.

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Affiliations

  1. INESC-ID and Instituto Superior Técnico, Universidade de Lisboa, IST-Taguspark, 2744-016 Porto Salvo, Portugal

    • Fernando P. Santos
    •  & Francisco C. Santos
  2. ATP-group, 2744-016 Porto Salvo, Portugal.

    • Fernando P. Santos
    • , Francisco C. Santos
    •  & Jorge M. Pacheco
  3. Centro de Biologia Molecular e Ambiental, Universidade do Minho, 4710-057 Braga, Portugal

    • Jorge M. Pacheco
  4. Departamento de Matemática e Aplicações, Universidade do Minho, 4710-057 Braga, Portugal

    • Jorge M. Pacheco

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Contributions

F.P.S., F.C.S. and J.M.P. conceived the project. F.P.S. performed the mathematical and numerical analysis. F.P.S., F.C.S. and J.M.P. analysed the results and wrote the paper. All authors contributed to all other aspects of the project.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jorge M. Pacheco.

Reviewer Information Nature thanks C. Efferson, E. Fehr, G. Szabó and A. Tavoni for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature25763

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