Evolution of Social Systems among Non-Human Primates: : Inequality and Equality Principles for Coexistence

Abstract

Besides sexual interactions and mother-offspring interactions, the social coexistence of individuals is based on two principles. The inequality principle urges an individual to behave in accordance with its dominant/subordinate relationship with others, while the equality principle works as if there were no dominant/subordinate inequality between individuals. Prevalence of either principle not only depends on the situational structure of the given event, but also on the phylogeny of the given species. By reviewing the dominance systems based on the inequality principle among Japanese macaques, I will probe into possible bases of social interactions based on the equality principle, and then trace the breakdown of the inequality principle and rise of the equality principle in the societies of the genus Pan, i.e., chimpanzees and pygmy chimpanzees.