The Cognitive Limit on Friendship
Robin Dunbar (1992) discovered that primate brain size predicts social group size. Extrapolating to humans, he found our neocortex can maintain about 150 stable relationships—people you know personally and could have a drink with if you ran into them. This limit has held across 2,000 years of human history, from hunter-gatherer tribes to Facebook friends.
Click a layer to learn more. Social networks aren't flat—they're nested circles.
Dunbar found brain size predicts group size across primates. Humans fit the pattern.
Typical band size across cultures: 100-230 members. The natural human community.
Archaeological evidence shows villages of 150-200 people before hierarchies emerged.
A century was ~80-100 soldiers; two centuries formed cohorts of 160.
W.L. Gore limits facilities to 150 employees—when it grows, they split.
Average user has 338 friends, but actively engages with ~150.
UK study: households send cards to ~150 people on average.
You can have 5,000 Facebook friends, but your brain still can't maintain more than ~150 real relationships. Social media creates the illusion of larger networks, but research shows engagement drops off at the same cognitive limits. Beyond 150, relationships become "one-way"—you know them, but they don't really know you. Technology changes communication, not cognition.