From Wikipedia dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships relationships in which an individual knows who each person is and how each person relates to every other person. This number was first proposed in the 1990s by British anthropologist Robin Dunbar who found a correlation between primate brain size and average social group size. By using the average human brain size and extrapolating from the results of primates he proposed that humans can comfortably maintain 150 stable relationships. There is some evidence that brain structure predicts the number of friends one has though causality remains to be seen. Dunbar explained it informally as the number of people you would not feel embarrassed about joining uninvited for a drink if you happen to bump into them in a bar.

Proponents assert that numbers larger than this general require more restrictive rules laws and enforce norms to maintain a stable cohesive group It has been proposed to lie between 100 and 250 with a commonly used value of 150. Dunbar’s number states the number of people one nose and keeps social contact with and it does not include the number of people known personally with a ceased social relationship nor people just generally known with a lack of persistent social relationship a number of which might be much higher and likely depends on long-term memory size. On the periphery the number also includes past colleagues such as high school friends with whom a person would want to reacquaint himself or herself if they met again.

Malcolm gladwell discusses the Dunbar number in his popular 2000 book called The tipping point. Gladwell describes the company WL Gore and associates now known for the Gore-Tex brand. By trial and error the leadership in the company discovered that if more than 150 employees were working together in one building different social problems could occur. The company started building company buildings with the limit of 150 employees and only 150 parking spaces. When the parking spaces were filled the company would build another 150 employee building. Sometimes these buildings would be placed only short distances apart. The company is also known for the open allocation company structure.