Dunbar’s Number

R. I. M. Dunbar, “Neocortex size as a constraint on group size in primates,” Journal of Human Evolution, vol. 22, pp. 469-493, 1992.

Dunbar’s number (approximately 150) is the cognitive limit on stable social relationships a human can maintain simultaneously, derived from neocortex size across primate species. Dunbar identified a hierarchy of group sizes: 5 (intimate support), 15 (close friends), 50 (personal network), 150 (meaningful social group), 500 (acquaintances), 1,500 (recognizable faces). Beyond 150, organizations fragment without formal structure.