Mammal societies Although a few types of structures prevail, social systems among mammals are relatively varied. New techniques, from monitoring to genetics, have allowed for a deeper understanding of this variation, how it is related to the environment, and how it has evolved. Clutton-Brock reviews the forms of and drivers of the different types of breeding systems and how they have been shaped by ecology and history. The author discusses how mammalian social interactions may be affected by human activities that are driving environmental change. —SNV