Generalized reciprocity in rats

I think it was Trivers who first came out with this notion of generalized reciprocity a while back. It never really gained that much attention in the literature, although I was always a fan of this notion for explaining human cooperation - because so many instances of cooperation can not be explained by just reciprocity. In this paper, not only do they discuss generalized reciprocity but they also find that it happens in rats...pretty cool! (the effect that they find doesn't appear to be very big, however)

Generalized Reciprocity in Rats

Claudia Rutte, Michael Taborsky

PLoS Biology, 5(7)

Abstract: The evolution of cooperation among nonrelatives has been explained by direct, indirect, and strong reciprocity. Animals should base the decision to help others on expected future help, which they may judge from past behavior of their partner. Although many examples of cooperative behavior exist in nature where reciprocity may be involved, experimental evidence for strategies predicted by direct reciprocity models remains controversial; and indirect and strong reciprocity have been found only in humans so far. Here we show experimentally that cooperative behavior of female rats is influenced by prior receipt of help, irrespective of the identity of the partner. Rats that were trained in an instrumental cooperative task (pulling a stick in order to produce food for a partner) pulled more often for an unknown partner after they were helped than if they had not received help before. This alternative mechanism, called generalized reciprocity, requires no specific knowledge about the partner and may promote the evolution of cooperation among unfamiliar nonrelatives.