Anthropologist Robin Dunbar's claim that the human neocortex caps our stable social world at roughly 150 relationships: the number behind village sizes, military companies, and the limit of who you can actually know.
Documented
The ratio
Documented: Dunbar's 1992 Journal of Human Evolution paper plotted primate neocortex ratio against social group size and extrapolated a human limit of about 148, rounded to 150, with a confidence interval roughly 100 to 230. Grooming, Gossip and the Evolution of Language (1996) argued language itself evolved as cheap grooming to hold that number. The layered structure, 5 intimates, 15 close, 50 friends, 150 meaningful, 500 known, 1500 faces, is documented in his subsequent work.
Assessment: Documented: the 1992 paper, the book, the layers. The confidence interval is wide and Dunbar publishes it.
Stories
The village evidence
The documented convergences: military companies from Rome to modern armies hover near 150, Hutterite communities split when they pass it, Neolithic villages and company-sized units recur at that scale across independent datasets. Gore-Tex famously caps its plants at about 150 employees on the same principle, cited in The Tipping Point.
Assessment: Documented: the military and communal datasets are published; the Gore-Tex practice is documented company policy. Convergence is not proof, and the card says so.
Interesting claims
The contested count
The documented challenge: Stockholm University analyses (2021) found the statistical basis shakier than the legend, the data compatible with limits anywhere from near 2 to over 500. Dunbar answered that the critics used outdated data and crude methods. The 150 survives as the most useful estimate ever published with a shrug attached, and the layered circles are the part most researchers accept.
Assessment: Interesting: the exact number is contested in print, by both sides, with new data. The village is real; its population is a range.
Sources and further reading
Robin Dunbar, 'Neocortex size as a constraint on group size in primates', Journal of Human Evolution 22, 1992 (primary paper, 148 extrapolation, CI 100-230)
Robin Dunbar, Grooming, Gossip and the Evolution of Language, 1996 (the grooming hypothesis)
Lindenfors et al., Stockholm University, 'The social brain hypothesis revisited', 2021 (the documented challenge)
Gore-Tex plant-size policy; Gladwell, The Tipping Point, 2000 (the applied case)
Worth asking
If the village is hardware, what exactly is the internet doing to it?