In Grooming, Gossip, and the Evolution of Language (ISBN 0674363361), the primatologist Robin Dunbar argues that humans are adapted for social group sizes of around 150 or less, a size that shows up in a number of traditional societies, as well as in present day groups such as the Hutterite religious communities. Dunbar argues that the human brain is optimized for keeping track of social relationships in groups small than 150, but not larger.