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Partners and rivals in direct reciprocity

A Publisher Correction to this article was published on 27 March 2018

This article has been updated

Abstract

Reciprocity is a major factor in human social life and accounts for a large part of cooperation in our communities. Direct reciprocity arises when repeated interactions occur between the same individuals. The framework of iterated games formalizes this phenomenon. Despite being introduced more than five decades ago, the concept keeps offering beautiful surprises. Recent theoretical research driven by new mathematical tools has proposed a remarkable dichotomy among the crucial strategies: successful individuals either act as partners or as rivals. Rivals strive for unilateral advantages by applying selfish or extortionate strategies. Partners aim to share the payoff for mutual cooperation, but are ready to fight back when being exploited. Which of these behaviours evolves depends on the environment. Whereas small population sizes and a limited number of rounds favour rivalry, partner strategies are selected when populations are large and relationships stable. Only partners allow for evolution of cooperation, while the rivals’ attempt to put themselves first leads to defection.

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Fig. 1: Repeated interactions allow evolution of cooperation.
Fig. 2: Eight strategies for the repeated PD.
Fig. 3: Adaptive players versus ZD strategies.
Fig. 4: Partners and rivals.
Fig. 5: Evolution favours partners or rivals.

Change history

  • 27 March 2018

    In the version of this Review Article originally published, in Fig. 4 an arrow pointing from ALLC to ALLD was mistakenly omitted. This has now been corrected in all versions of the Review Article.

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Acknowledgements

This work was supported by the European Research Council Start Grant 279307: Graph Games (to K.C.), Austrian Science Fund (FWF) Grant P23499-N23 (to K.C.), FWF NFN Grant S11407-N23 Rigorous Systems Engineering/Systematic Methods in Systems Engineering (to K.C.), Office of Naval Research Grant N00014-16-1- 2914 (to M.A.N.) and the John Templeton Foundation (M.A.N.). C.H. acknowledges generous support from the ISTFELLOW programme.

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Hilbe, C., Chatterjee, K. & Nowak, M.A. Partners and rivals in direct reciprocity. Nat Hum Behav 2, 469–477 (2018). https://doi.org/10.1038/s41562-018-0320-9

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