Involuntary defection and the evolutionary origins of empathy

An occasional involuntary defection (IVD)—being unable, rather than unwilling, to donate help to others—is an intrinsic attribute of reciprocal cooperation (2003. J. Theor. Biol. 225–285). In fact, it is easy to see that—barring special circumstances—individuals that can donate help whenever requested do not need help of the same kind from others. That is, it is by no means clear why such individuals should participate in symmetric reciprocity interactions.In this paper, I analyse the consequences of introducing IVD into direct reciprocity modeling and show that a simple form of empathy—not retaliating after being punished for IVD—is a prerequisite for evolutionarily stable cooperation. Furthermore: we will see that the stability of this, empathic retaliator, strategy increases with the number of opportunities for cooperative exchanges in the life of an average individual.