Flexible and Derived Varieties of Mammalian Social Organization: Promiscuity in Aggregations May Have Served as a Recent “Toolkit” Giving Rise to “Sexual Segregation,” Polygynous Social Structures, Monogamy, Polyandry, and Leks

Chapter 3 argues that extant mammals are characterized by an ancient social “toolkit” derived from the traits of ancient group-living mammals. An important lesson highlighted by a review of extant social evolution is that animals in heterogeneous regimes are not necessarily group living, although, extreme environments (sublethal stress?) appear to favor higher grades of sociality. A review of the literature suggests that flexible social structures evolved from “promiscuous” aggregations of reproductive males and females characterized by nonoverlapping ranges and that body sizes, home-range sizes, and male–male tolerance are driven by evolution in thermal (“patch”) regimes.