Kin selection, not indirect reciprocity, explains helping those who help others in image scoring

Helping those who help others appears to be a widespread phenomenon. It is typically framed as indirect reciprocity in which individuals who are seen to help later receive returns from third parties. However, indirect reciprocity only works when individuals condition their help not just on how their recipient has behaved in the past but also on whether their recipient was justified in behaving that way. It also requires sufficient repeated interactions of this type among other individuals for a benefit to be reciprocated. These factors limit the scope of indirect reciprocity to explain cases where people do help those who help others. Here, I propose instead that helping can be explained by the indirect fitness benefits (or relatedness) that result from helping other helpers in groups. This means that when individuals help other helpers, they may not make any returns via indirect reciprocity, but rather they may be helping a strategy of helping those who help. In this way, the helping strategy can spread even when helping has no net benefit to the individual helper. This is a form of relatedness in which individuals help their kin that are recognized by their helping behaviour. As such, conditional helping is likely to be found where population structure promotes relatedness through non-random association. The analysis suggests indirect reciprocity may not have played the decisive role in the evolution of human cooperation that is often thought, but paradoxically that the use of image scores deserves renewed attention as a strategy of helping those with the same behaviour.