If a chimpanzee ventures into the territory of a different group, it will almost certainly be killed. But a New Yorker can fly to Los Angeles–or Borneo–with very little fear. Psychologists have done little to explain this: For years, they have held that our biology puts a hard upper limit of about 150 people on the size of our social groups. But human societies are in fact vastly larger. How do we manage—by and large—to get along with each other?

Drawing on his new book, The Human Swarm: How Our Societies Arise, Thrive, and Fall, Mark W. Moffett, a biologist and Smithsonian research associate in entomology, discusses how sprawling, highly complex civilizations have been created, and what it takes to sustain them. He examines findings in psychology, sociology, and anthropology that explain the social adaptations that bind members of societies, and explores how the tension between identity and anonymity defines how those groups work—and sometimes don’t.

Copies of The Human Swarm (Basic Books) are available for purchase and signing. 

Mark W. Moffet’s research into the world of ants reveals striking parallels between their behavior and those of humans. As a guest on “The Colbert Report,” he described the elaborate social structures of ants that include market economies and nationalism.