Dunbar's Number

Definition: "Dunbar's Number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is and how each person relates to every other person. This number was first proposed 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 only comfortably maintain 150 stable relationships." Quoted from Wikipedia on "Dunbar's number" Also, see the curious article, "Dunbar’s Number Kicked My Ass in Facebook Friends Experiment"