«Active» selection may participate in the evolution of primates

Abstract

Selection pressures in the evolution of morphological characters which are exclusive to primates were discussed. While the evolutionary change in some morphological characters of primates can be explained by natural or sexual selection, there are also morphological characters of primates, such as some regions of neocortices, which are involved in social interactions and whose evolutionary changes can hardly be explained by natural or sexual selection alone. Furthermore, recent studies have demonstrated that relative sizes of brain, neocortex and some thalamic nuclei of brains differ significantly by social structure in primates. Based on these and other findings, we propose here that “active” selection pressures may have favored a variety of morphological characters related to social interactions, the selection pressures which are derived from social interactions and are operative within animals or troops. The introduction of concept of active selection will be useful in developing conceptual frameworks for understanding of the mechanism of evolution of primates, in particular, of hominids.