Abstract
Indirect reciprocity is a mechanism for the evolution of cooperation based on social norms. This mechanism requires that individuals in a population observe and judge each other’s behaviors. Individuals with a good reputation are more likely to receive help from others. Previous work suggests that indirect reciprocity is only effective when all relevant information is reliable and publicly available. Otherwise, individuals may disagree on how to assess others, even if they all apply the same social norm. Such disagreements can lead to a breakdown of cooperation. Here we explore whether the predominantly studied ‘leading eight’ social norms of indirect reciprocity can be made more robust by equipping them with an element of generosity. To this end, we distinguish between two kinds of generosity. According to assessment generosity, individuals occasionally assign a good reputation to group members who would usually be regarded as bad. According to action generosity, individuals occasionally cooperate with group members with whom they would usually defect. Using individual-based simulations, we show that the two kinds of generosity have a very different effect on the resulting reputation dynamics. Assessment generosity tends to add to the overall noise and allows defectors to invade. In contrast, a limited amount of action generosity can be beneficial in a few cases. However, even when action generosity is beneficial, the respective simulations do not result in full cooperation. Our results suggest that while generosity can favor cooperation when individuals use the most simple strategies of reciprocity, it is disadvantageous when individuals use more complex social norms.
Highlights
Every time the donor cooperates, and it should deteriorate every time the donor defects
In situations in which they would usually defect, they may occasionally cooperate instead. These two kinds of generosity may seem similar, our results suggest that their effect on the resulting reputation dynamics is very different
Our results suggest that complex social norms of indirect reciprocity are not compatible with individual acts of generosity
Summary
Every time the donor cooperates, and it should deteriorate every time the donor defects. The reason for this instability is that individuals are required to defect against an ill-reputed group member; yet by doing so, they harm their own reputation To overcome this inconsistency, it has been argued that stable norms of indirect reciprocity need to be sufficiently complex to differentiate between justified and unjustified acts of d efection[22,23]. The analogous first-order social norm ‘Generous Scoring’ has been shown to be stable in the context of indirect r eciprocity[44], even though classical Image Scoring is not In both cases, there is the same intuition for why a certain degree of generosity is favorable. Unless generosity is the result of a coordinated effort among all population members, generosity merely acts as another seed of disagreement
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