AbstractHow do moral systems evolve? The common view, rooted in game theory, is that cooperation and mutual aid require tight partnerships among individuals, or close kinship. But this dogma is now being shaken and, on page 573 of this issue, Nowak and Sigmund report a new mathematical model to show that cooperation can become established even if recipients have no chance to return the help to their helper. This is because helping improves reputation, which in turn makes one more likely to be helped. Nowak and Sigmund's stance differs radically from classical approaches, because they assume that any two organisms are unlikely to interact twice. This excludes any direct reciprocity, meaning that you should not expect your assistance to be returned by somebody you helped on a previous encounter, but by somebody else. For such indirect reciprocity to work, individuals must assess others in their group by watching their games from the sidelines and assigning 'image scores' to them. If you watch one individual helping another, you can allot him or her one point of image score; but if you witness the individual refusing to help, withdraw one point. Then, when you are asked to help, you will cooperate if your partner's score is otherwise, you defect (that is, you don't cooperate). Strategies can be more or less discriminating according to their 'score cut'. For example, a 'cooperative' strategy has a score cut of zero or less, meaning that the individual then cooperates with other individuals on their first interaction...
Ferriere R <http://pure.iiasa.ac.at/view/iiasa/1248.html> (1998). Help and you shall be helped. Nature 393 (6685): 517-519. DOI:10.1038/31102 <https://doi.org/10.1038/31102>.