A group of researchers from the University of Berne, Switzerland has shown that rats will help other rats whenever they have recieved help themselves before regardless of the identity of the new reciever. This is called "Generalized Reciprocity" and is shown for the first time in nonhumans.

 

The results are congruent with recent theoretical models that suggest that cooperation can evolve even without individual recognition in small groups. It works because the previous interactions - even if anonymous - provide pointers to the overall level of cooperation within a small group. Although rats helped by anonymous helpers became generally more helpful, help is elevated even more towards recognized helpers consistent with theory and earlier results. Reference: Generalized Reciprocity in Rats Rutte C, Taborsky M PLoS Biology Vol. 5, No. 7, e196 doi:10.1371/journal.pbio.0050196