Resilient Cooperators Stabilize Long-run Cooperation In The Finitely Repeated Prisoner’s Dilemma

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Learning in finitely repeated games of cooperation remains poorly understood in part because their dynamics play out over a timescale exceeding that of traditional lab experiments. Here, we report results of a virtual lab experiment in which 94 subjects play up to 400 ten-round games of Prisoner’s Dilemma over the course of twenty consecutive weekdays. Consistent with previous work, the typical round of first defection moves earlier for several days; however, this unravelling process stabilizes after roughly one week. Analysing individual strategies, we find that approximately 40% of players behave as resilient cooperators who avoid unravelling even at significant cost to themselves. Finally, using a standard learning model we predict that a sufficiently large minority of resilient cooperators can permanently stabilize unravelling among a majority of rational players. These results shed hopeful light on the long-term dynamics of cooperation, and demonstrate the importance of long-run experiments.

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Nature Communications
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Note: At the time of this publication, Dr. Duncan Watts was affiliated with Microsoft Research. Currently, Dr. Duncan J. Watts is Stevens University Professor at the University of Pennsylvania, and Professor in Department of Computer and Information Science in the School of Engineering and Applied Science, Annenberg School for Communication, and Department of Operations, Information and Decisions in the Wharton School.
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