The Evolution of Primate Social Systems and Social Complexity: The Promise and Challenge of Comparative Phylogenetic Methods

Social systems vary across the primate order, both within and between major lineages. Understanding how and why this variation arises and how social systems have changed over the radiation is a major focus of comparative primate evolutionary biology. For anthropologists in particular, the issue of social evolution resonates strongly because of interest in how certain aspects of human social systems—e.g., multilevel societies, divisions of labor—have come about. For primatologists, interest centers more around understanding the evolution of particular kinds of sociality (e.g., solitary versus various forms of group living); the variation observed in mating, breeding, and care systems; and the adaptive value of relationships. Attention has also been paid to the evolution of social “complexity,” although that concept is ill-defined and complicated by our human-centered perspective on the natural world. Here, I review 50 years of research on primate social evolution and how comparative phylogenetic approaches have informed that work, while offering some cautions and suggestions for the future.