Associative Effects: Competition, Social Interactions, Group and Kin Selection
The phenotypes of those individuals with which an focal individual interacts often influences the trait value in the focal individual. Maternal effects is a classic example of this phenomena, as is fitness. If these traits are heritable, then the selection response depends on both the change in the direct effects influencing a target trait and the associative effects contributed by interacting individuals. In such a setting, the breeder's equation no longer holds, as the problem is now a multiple trait one. This chapter examines the theory of response under models with both direct and associative effects, which can lead to a reversed response (a trait selected to increase instead decreases). The evolution of behavioral traits, including the evolution of altruism, is best handled using this approach. Further, kin and group selection follow as special cases of the gerenal model under multilevel selection. This chapter also examines how mixed models can be used estimate model parameters.