Robin Dunbar is an anthropologist who studied at Oxford during the second half of the 20th century. He researched and calculated the number of social relationships individuals of certain species can sustain- now known as Dunbar's Number.
-Chimpanzees can sustain 50 allies (close relationships)
-Humans on average can sustain 150 close relationships
(The size of a species brain has a positive correlation to the possible number of social relationships sustained)
These findings are not black and white because it is hard to look at friendships as being strictly present or not present. There is a spectrum to how comfortable we are around certain individuals, but Dunbar described these social relationships as people you would be comfortable getting a drink with at a bar.
We do not interact with everyone in our societies and generally there are more than 150 people in a society, so we pick and choose who we will befriend. Even if a society consisted of 150 people we would likely diverge into distinct groups with differing social networks.