The Effect of Group Size and Frequency-of-Encounter on the Evolution of Cooperation

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We introduce a model of the evolution of cooperation in groups which incorporates both conditional direct-reciprocity (“tit-for-tat”), and indirect-reciprocity based on public reputation (“conspicuous altruism”). We use ALife methods to quantitatively assess the effect of changing the group size and the frequency with which other group members are encountered. We find that for moderately sized groups, although conspicuous altruism plays an important role in enabling cooperation, it fails to prevent an exponential increase in the level of the defectors as the group size is increased, suggesting that economic factors may limit group size for cooperative ecological tasks such as foraging.