The Human Swarm: How Our Societies Arise, Thrive, and Fall

Imagine standing in a bustling train station, watching the swarm of humanity move beneath the grand clock. Each person is part of a larger whole, yet no one knows everyone else personally. What makes this crowd a society is not just their cooperation or their shared space, but a deeper, invisible bond: a shared identity that marks who belongs and who does not. Societies are more than mere groups of cooperating individuals; they are defined by stable membership and a collective sense of 'us' versus 'them'. This distinction is fundamental and ancient, extending beyond humans to many animal species.

One might think cooperation is the glue holding societies together, but cooperation alone doesn’t explain the vast scale of human societies. Our brains limit us to maintaining about 150 close relationships, a concept known as Dunbar's number. Yet, human societies range from thousands to billions. This disparity suggests that societies rely on markers and shared symbols to extend identity beyond personal acquaintance.

Consider that even chimpanzees, our closest relatives, live in communities rarely exceeding 200 members because they must recognize each individual. Humans broke this limit by developing ways to identify society members anonymously, such as language, dress, and customs.

Understanding society as a shared identity helps explain why people are willing to sacrifice for their nation or tribe, even without knowing most members personally. It also sheds light on the deep-rooted nature of ingroup and outgroup distinctions, which have shaped human history profoundly.

As we move forward, we will explore how these identities are formed and maintained, how societies function internally, and how they expand beyond the limits of individual recognition. The next section delves into the remarkable ways societies can grow large by relying on anonymous membership and markers of identity.