The Econ­o­mist looks at whether Dunbar’s num­ber, the sup­posed limit of sta­ble social rela­tion­ships, holds true on social net­work­ing sites.

That […] 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. […]

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.

Two items of note: Face­book has an “in-house soci­ol­o­gist”; and this man, Dr Cameron Mar­low, reveals that the aver­age num­ber of friends cor­re­lates pretty closely to Dunbar’s number.

via Mind Hacks