Reciprocal altruism and group formation: The degree of segmentation of reciprocal altruists who prefer 'old-helping-partners'

To what degree does reciprocal altruism add to the explanation of the human way of group living? That is the main question of this paper. In order to find an answer to this question, we use the Social Evolution Model (SEM) that has been developed earlier. It allows us to investigate both the conditions under which cooperation is a viable strategy and the conditions under which individuals structure themselves in stable groups. In the SEM, exchange relationships are created on the basis of asking for help and providing support in an initially unstructured population. We study whether, and to what extent, this process results in a socially segmented population. First we arrive at the conclusion that there is no analytical solution to some minimal group size that guarantees group survival in which all individuals are reciprocal altruists. If there is anything, then it is an optimal instead of a minimal group size. Our simulation results suggests that on the basis of our present assumptions some degree of group formation does appear, but not to the extent that we 'see' in real life exchange settings