dunbars-numberlisted

# Dunbar's Number ## Overview **Dunbar's number** (~150) is the cognitive limit on stable social groups the human neocortex can sustain, with nested layers at ~5, ~15, ~50, then outer bands at ~500 and ~1,500. Derived by Robin Dunbar (1992) from primate neocortex ratios. Key implication: **below ~150, informal trust coordinates behavior; above ~150, formal hierarchy becomes architecturally mandatory** — not a cultural choice. Composes with [`network-effects`](../network-effects/SKILL.md) (different coordination mechanisms below vs. above 150), [`principal-agent`](../principal-agent/SKILL.md) (exceeding 150 multiplies agency problems informal trust can no longer cover), [`founder-mindset`](../founder-mindset/SKILL.md) (founder relationship bandwidth peaks at ~150 — first breakpoint demanding shift from doing to delegating structure). ## When to Use - Headcount approaching or crossing 150 (or 50, or 500) - "Coordination getting harder" complaints with no obvious structural cause - Deciding to split a team, open a new office, or create a sub-unit - Designing org structure for a scaling startup; evaluating acquisition integration plans - Diagnosing why informal culture "felt different" after a headcount milestone **Not when:** group well below 50 and problems are interpersonal; constraint is incentive misalignment (use [`principal-agent`](../principal-agent/SKILL.md)); challenge is growing a network beyond 150 (use [`network-effects`](../network-effects/SKILL.md)). ## Coac