a cognitive ceiling on stable relationships: roughly 150 people one mind can track well enough to know who they are and how they relate to everyone else. Robin Dunbar found the figure by correlating neocortex size across primates with typical group size, then reading the same ratio onto humans — an anthropological estimate, not a derived constant; published ranges for humans run roughly 100 to 250
past the number a group does not grow denser, it fissions: clans, companies, army units cluster near 150, then split into new units rather than piling onto one
in referral the number sets $D$, the referrer's equilibrium cell size rather than a hard cap: past $D$ the share curve flattens to the floor and growth continues by delegation — a referee builds a branch of their own instead of stacking onto the same referrer
see referral
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