Social Subordination, Population Density, and Mammalian Evolution

Natural selection, operating on phenotypic expressions of the genetic material, is generally held to be of fundamental importance in evolution. Natural selection includes environmental selection, by which is meant here the selection of particular correlated phenotypic-genotypic changes or adaptations that confer better survival, including competitive advantages of the genotype, in a new or changing environment. However, the behavioral characteristics of many, if not most, mammals operate to reduce exposure to new or changing habitats. For example, most mammals are reluctant to go beyond the limits of familiar territory-their home range-and generally must be forced to do so. In addition, socially dominant animals usually occupy and hold the most desirable portions of the habitat and are the most successful breeders. In turn, their offspring tend to be dominant. Moreover, mammals generally occupy the habitat for which they are best adapted, and a given species may occupy similar, if not identical, habitats for many millennia. Therefore, if animals occupy a specific habitat and move with it as the habitat shifts with time and climatic change, how can they be subjected to the selective force of environmental changes, and by which mechanisms does mammalian evolution occur? Mammalian evolution might be expected to be conservative and limited to a rate characteristic of the entire ecosystem. However, mammalian evolution has been explosive with respect to rate and diversity. I suggest that the conservative influence of social dominance is more than offset by other consequences of hierarchical behavior, and that social behavior is a major force in the evolution