Mutation enhances cooperation in direct reciprocity

TL;DR

This paper shows that intermediate mutation rates can promote high cooperation levels in direct reciprocity, even with low benefit-to-cost ratios, by fostering diversity and community resilience.

Contribution

It reveals that mutation-induced diversity enhances cooperation in direct reciprocity, even when benefit-to-cost ratios are marginally above one.

Findings

Mutation leads to diverse cooperative communities.

Diversity undermines defector stability.

High cooperation achieved at low benefit-to-cost ratios.

Abstract

Direct reciprocity is a powerful mechanism for evolution of cooperation based on repeated interactions between the same individuals. But high levels of cooperation evolve only if the benefit-to-cost ratio exceeds a certain threshold that depends on memory length. For the best-explored case of one-round memory, that threshold is two. Here we report that intermediate mutation rates lead to high levels of cooperation, even if the benefit-to-cost ratio is only marginally above one, and even if individuals only use a minimum of past information. This surprising observation is caused by two effects. First, mutation generates diversity which undermines the evolutionary stability of defectors. Second, mutation leads to diverse communities of cooperators that are more resilient than homogeneous ones. This finding is relevant because many real world opportunities for cooperation have small benefit-to-cost ratios, which are between one and two, and we describe how direct reciprocity can attain cooperation in such settings. Our result can be interpreted as showing that diversity, rather than uniformity, promotes evolution of cooperation.