Dunbar's Number
Robin Dunbar's finding that human social ties sort into nested rings rather than one flat list: a support clique of about five people, a sympathy group of about fifteen, then wider bands of fifty and a hundred and fifty. Robin Dunbar and Matt Spoors defined the innermost ring in 1995 by asking who people would turn to in severe emotional, social or financial trouble, not who they liked best. The outer figure of 150 is the most quoted part of the model, and the most argued over.
What it is
Most people, asked to describe their social world, reach for a single number: how many friends, how many contacts, how big the group chat has become. Dunbar's research suggests that number is the wrong unit. Social ties arrange themselves into layers, each one wider and looser than the last, and the layers turn up with striking consistency across the people he studied.
Working with Matt Spoors, Dunbar surveyed people's support networks and kept finding the same shape: an innermost circle of around five, a next layer of about fifteen, then bands widening to roughly fifty and a hundred and fifty. Reported in "Social networks, support cliques, and kinship" in the journal Human Nature in 1995, the finding held up even when the question was put bluntly. Rather than asking who someone liked, Dunbar and Spoors asked who they would go to if their life fell apart: a job lost, a relationship ending, a diagnosis received. The five or so names that came back defined the support clique, and the definition mattered. It meant the innermost ring was not a popularity measure. It was a functional one, sorted by who actually shows up.
Move outward and the rings loosen. The sympathy group of about fifteen is who you would notice missing from a gathering. The band of fifty is people whose lives you follow in outline rather than in detail. The outer figure of 150, the one that escaped the academic literature and became "Dunbar's number" in general use, is roughly the group a person can plausibly maintain a relationship with at all: the size of a wedding guest list, or of a village where everyone still knows everyone. Emotional intensity falls steadily as the numbers climb. More contacts, thinner ties.
The 150 figure is the part most people have heard of, and it is also the part later work has pushed back on hardest. Estimates of the upper bound have varied across studies and methods, and some researchers argue the number is not as fixed as its popularity in management books and social-media commentary would suggest. The layered shape itself, a tight support clique nested inside progressively looser rings, has replicated more consistently than the specific ceiling of 150.