"Indirect Reciprocity and the Evolution of Morals"
Indirect reciprocity serves as a framework for understanding large-scale human cooperation and is based on the idea that a player who cooperated gains the return back not from the beneficiary, as in direct reciprocity, but from a third person, who knows of his good deed through reputation. This can work if the cost of an altruistic act if offset by a raised 'score' or status, which increases the chance to subsequently become the recipient of an altruistic act. Cooperation is channeled towards the 'valuable' members of the community, and involves reputation and status. Ever since image-based models for indirect reciprocity were introduced, the relative merits of scoring vs. standing have been discussed to find out how important it is to differentiate between justified and non-justified defections. This is analogous to the question whether punishment can sustain cooperation even when it is costly. We show that an answer to this question can depend on details of the model, for instance concerning the probability distribution of the number of interactions experienced per player. We use extensive individual-based simulations to compare scoring, standing and other forms of assessing defections, and show that several forms of indirect reciprocation can robustly sustain cooperation.