# Robin Dunbar The British anthropologist and evolutionary psychologist who **identified the cognitive limit on stable human social relationships** — approximately 150 — that has become known as the Dunbar Number. Dunbar (b. 1947) is Professor of Evolutionary Psychology at the University of Oxford. His 1992 paper "Neocortex size as a constraint on group size in primates" (*Journal of Human Evolution*) established the correlation between primate brain size and average group size; extrapolating the regression to human neocortex size produces the ~150 estimate. ## Career and contribution **Background.** University of Oxford (BA, PhD). Long career studying primate behavior in the field and applying insights to human evolutionary psychology. Positions at Cambridge, University of Liverpool, and University of Oxford. **The neocortex-group-size correlation.** The 1992 paper's key finding: across primate species, average group size correlates strongly with relative neocortex size. The interpretation is that maintaining social relationships is cognitively expensive; bigger brains support bigger groups. Extrapolating the regression to humans produces approximately 150 as the predicted average group size — and 150 turns out to be remarkably consistent with observed human group sizes across cultures and contexts (Neolithic villages, military companies, Hutterite religious communities, professional networks). **Layered social structure.** Subsequent research identified that Dunbar's framework is more accurately a layered structure: ~5 (closest intimates), ~15 (close friends), ~50 (good friends), ~150 (stable contacts), ~500 (acquaintances), ~1,500 (recognized faces). The layers scale approximately by a factor of 3 between levels. The ~150 figure is the most-cited but the layered structure is the actual finding. **Cross-cultural verification.** Dunbar and collaborators have verified the ~150 estimate across many contexts: traditional hunter-gatherer band sizes, military unit sizes, religious-community sizes, professional-network sizes, and social-media follower-engagement patterns. The cross-context consistency is strong evidence that the underlying cognitive constraint is real. ## KB significance **Why mass-scale politics produces specific distortions.** Modern political life operates far beyond the Dunbar limit. Voters interact with politicians through media rather than personally; political "communities" of millions are not communities in the cognitive sense Dunbar's framework requires. The resulting dynamics (parasocial relationships with politicians, identity-tribal sorting, outrage politics) are partially predictable from the scale mismatch between political organization and human social cognition. See Dunbar Number for the full treatment. ## See also - Dunbar Number — the eponymous concept - [[Bounded Rationality]] — broader frame for cognitive constraints