It references research by anthropologist Robin Dunbar, now at Oxford. Dunbar suggests that the brain is efficient and because keeping up with too large a group is too time-consuming, there is a finite number. Dunbar suggests that number is 148.
(Primates on Facebook: http://www.economist.com/science/displaystory.cfm?story_id=13176775).
Here are snipets from the article:
Primatologists call some of the things that happen on social networks “grooming”. In the wild, grooming is time-consuming and here computerisation certainly helps. But keeping track of who to groom—and why—demands quite a bit of mental computation. You need to remember who is allied with, hostile to, or lusts after whom, and act accordingly.
Robin Dunbar, an anthropologist who now works at Oxford University, concluded that the cognitive power of the brain limits the size of the social network that an individual of any given species can develop. Extrapolating from the brain sizes and social networks of apes, Dr Dunbar suggested that the size of the human brain allows stable networks of about 148. Rounded to 150, this has become famous as “the Dunbar number”.
Many institutions, from neolithic villages to the maniples of the Roman army, seem to be organised around the Dunbar number. Because everybody knows everybody else, such groups can run with a minimum of bureaucracy.
Sociologists also distinguish between a person’s wider network, as described by the Dunbar number or something similar, and his social “core”. Peter Marsden, of Harvard University, found that Americans, even if they socialise a lot, tend to have only a handful of individuals with whom they “can discuss important matters”. A subsequent study found, to widespread concern, that this number is on a downward trend.
The rise of online social networks, with their troves of data, might shed some light on these matters. So The Economist asked Cameron Marlow, the “in-house sociologist” at Facebook, to crunch some numbers. Dr Marlow found that the average number of “friends” in a Facebook network is 120, consistent with Dr Dunbar’s hypothesis, and that women tend to have somewhat more than men.
What also struck Dr Marlow, however, was that the number of people on an individual’s friend list with whom he (or she) frequently interacts is remarkably small and stable. The more “active” or intimate the interaction, the smaller and more stable the group.
What mainly goes up, therefore, is not the core network but the number of casual contacts that people track more passively.
Put differently, people who are members of online social networks are not so much “networking” as they are “broadcasting their lives to an outer tier of acquaintances who aren’t necessarily inside the Dunbar circle,” says Lee Rainie, the director of the Pew Internet & American Life Project, a polling organisation. Humans may be advertising themselves more efficiently. But they still have the same small circles of intimacy as ever.