Abstract

A prominent explanation of the evolution of altruism is ‘indirect reciprocity’ where the tracking of reputations in a population promotes altruistic outcomes. This paper investigates the conditions under which the meaning of reputation-tracking signals can co-evolve with altruistic behaviours. Previous work on this question suggests that such a co-evolution is unlikely. In our model, we introduce a mixture of direct and indirect information: individuals directly observe the actions and signals of others with some probability, rather than individuals always relying only upon information conveyed through signals. In this context, we see the co-evolution of altruism and the kind of ‘moral signals’ required for individuals to track reputation. Our interpretation of this model is that, although individuals can sometimes observe the behaviour of their fellows directly, they cannot always do so, and signals evolve to fill this gap. Although ‘can’ does not imply ‘must’—that our model can produce this co-evolution does not establish that we have found the only possible mechanism—we nonetheless consider this an interesting possibility result worthy of further investigation.