Primates on Facebook

THAT Facebook, Twitter and other online social networks will increase the size of human social groups is an obvious hypothesis, given that they reduce a lot of the friction and cost involved in keeping in touch with other people. Once you join and gather your “friends” online, you can share in their lives as recorded by photographs, “status updates” and other titbits, and, with your permission, they can share in yours. Additional friends are free, so why not say the more the merrier?

But perhaps additional friends are not free. Primatologists call at least 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. Several years ago, therefore, 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”.