Dunbar's Number
Robin Dunbar · 1992
"Dunbar proposed humans can maintain roughly 150 stable social relationships, capped by neocortex size — beyond that, groups need hierarchy, rules, or substructure to stay coherent."
Dunbar correlated primate neocortex size with group size and predicted human groups stabilize around 150 — the largest village that still runs on gossip instead of formal structure.
The 150 is not magic but layered: ~5 intimate, ~15 close, ~50 friends, ~150 meaningful contacts, then acquaintances. Relationship maintenance scales with time and cognitive tracking; beyond the limit, informal reciprocity breaks and defection rises unless you add roles, rituals, or software. Military companies, Hutterite colonies, and effective Discord communities cluster near the same bands for the same reason.
What constrains Dunbar's number according to Dunbar's original argument?
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The explanation above is written with AI assistance. These are the originals — go to them to check it.
- Neocortex size as a constraint on group size — Dunbar's numberRobin Dunbar / Wikipedia
Reed's Law & Group-Forming Networks
"Reed argued that tools that let users form groups — not just connect one-to-one or broadcast one-to-many — have value that scales as 2^n, vastly outpacing Metcalfe's n², because the number of possible subgroups explodes."