Partners and Rivals in Direct Reciprocity

A new study by Martin Nowak examines how strategies can foster or destroy cooperation.  “If you consider all strategies of direct reciprocity, a very small subset of them are either partners or rivals, but evolution always leads to one or the other,” says Nowak. The study in Nature Human Behavior  finds that across repeated interactions, the environment that individuals find themselves in can affect whether they act as partners or rivals. Only partners allow for evolution of cooperation, while rivals attempt to put themselves first, which leads to defection.  The Harvard Gazette