The Evolution of Altruism by Kin Selection: New Phenomena With Strong Selection

The development of a theory of kin selection has proceeded along two lines. Inclusivefitness models have implicitly assumed that sel~tion is weak, whereas exact-population genetic models place no constraints on the strength of selection. Several examples are presented showing that qualitatively new behavior has emerged from the exact models. However, for many problems, the exact-population and inclusive-fitness models often yield identical results. Unfortunately, it is not possible to identify a priori those problems that can be handled sufficiently by the simpler inclusive-fitness models. The initial increase of cooperative behavior in a population of egoists involves diiculties similar to the Initial increase of altruism. Clustering of cooperatives produces dynamics for the increase of cooperation that are formally similar to population models of inbreeding. Here, an increase in the tendency to cluster is equivalent to increasing the “relationship” among cooperatives, and therefore augments the chance for cooperation to increase.