The story
Proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size.
Etymology from Wiktionary, CC BY-SA 4.0.
Dunbar's number
Today it means: A suggested cognitive limit to the number of people with whom one can maintain stable social relationships. It has been proposed to lie between 100 and 250, with a commonly used value of 150. Full definition →