Quartz 4

Dunbar's number

2 min read

Dunbar’s Number

What It Is

Dunbar’s Number (~150) is the cognitive limit on the number of stable social relationships a person can maintain — relationships where you know who each person is and how they relate to you. Proposed by anthropologist Robin Dunbar in the 1990s, based on the correlation between primate neocortex size and social group size.

The number isn’t a hard cliff — it’s more of a layered structure:

  • ~5 — intimate circle (closest support)
  • ~15 — close friends
  • ~50 — good friends
  • ~150 — meaningful acquaintances / stable community
  • ~500 — acquaintances
  • ~1500 — faces you recognize

Why It Matters for the CLT

At 150 people or fewer, relational accountability functions naturally. You don’t need institutional enforcement of norms because social pressure and genuine care do the work. Helping a neighbor isn’t abstract altruism — it’s of course you do that because you know them.

This is the scale at which the cosmological “why” (religious belief, ideology) becomes unnecessary. The relational “why” is sufficient.

The practical implication: the CLT community should probably not exceed ~150 residents if it wants to preserve the village dynamic. Growth beyond that likely requires spinning off new communities rather than scaling the existing one.

The Governance Implication

Dunbar’s number also explains why large organizations need bureaucracy — rules substitute for relationships when you can’t know everyone. Keeping the community within Dunbar’s range means governance can stay light and relational rather than procedural and institutional.

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