Evolutionary Significance of the Role of Family Units in a Broader Social System

Indirect benefits to individual fitness in social species can be influenced by a variety of behavioral factors. Behaviors which support the fitness of kin provide indirect benefits in the form of evolutionary success of relatives. Further, individuals may obtain additional indirect benefits via participation in a well-organized social environment. Building on previous models of selfishly-motivated self-organizing societies, we explore the evolutionary trade-off between inclusion and maintenance of family groups and the ability of a population to sustain a well-organized social structure. Our results demonstrate that the interactions between Hamiltonian and organizationally-based indirect benefits to individual fitness interact to favor certain types of social affiliation traits. Conversely, we show how particular types of social affiliation dynamics may provide selective pressures to limit the size of behaviorally-defined familial groups. We present the first studies of the evolution of social complexity differentiating affiliation behavior between kin and non-kin.