In contrast , anthropologist H. Russell Bernard and Peter Killworth have done a variety of field studies in the United States that came up with an estimated mean number of ties , 290 , roughly double Dunbar 's estimate .
That is known as Dunbar 's number .
Anthropologist H. Russell Bernard and Peter Killworth have done a variety of field studies in the United States that came up with an estimated mean number of ties , 290 , roughly double Dunbar 's estimate .
That is known as Dunbar 's number .