To quote from Wikipedia, Dunbar's number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows who each person is, and how each person relates to every other person. Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. No precise value has been proposed for Dunbar's number. It has been proposed to lie between 100 and 230, with a commonly used value of 150. Dunbar's number states the number of people one knows and keeps social contact with, and it does not include the number of people known personally with a ceased social relationship, nor people just generally known with a lack of persistent social relationship, a number which might be much higher and likely depends on long-term memory size.
Like me, I'm sure that you know people who seem to remember everything said by everyone, however long ago. Perhaps like me you recognise your own inability to do the same. In my job I find that I have to interact with a huge number of people, and I often find myself completely unable to remember the name of someone who I have known for years.
|Robin Dunbar - a touch is worth a thousand words any day!|
Whether or not Dunbar's hypothesis about neocortical processing capacity or theories about long term memory are the perfect explanations of the phenomenon, I think almost all of us recognise the feeling. You can see him speaking about Facebook friends and 'real friends' and related topics in an excellent 19 minute long talk on ForaTV. See Robin Dunbar: How Many Friends Does One Person Need? He says that he thinks touch is one of the most important factors in maintaining a real relationship and discusses the role of kinship, and talks about the fragility of friendships. Interestingly it seems that the limit to the number of friends seems to be largely limited to primate species too.
A recent episode of the always-interesting podcast, Skepticality, featured an interview with David McRaney at this link You Are Not So Smart. In a discussion that covered a huge range of interesting topics he mentioned that studies of people's use of social media have been used to test Dunbar's number in a new way.
Looking into this I found one such study of Twitter users. Validation of Dunbar’s Number in Twitter by Bruno Goncalves et al seems to confirm the idea, with a sample of 1.7 million individuals, 380 million tweets and 25 million conversations. The magic number of contacts comes out at around 200 again.
Small note: I must admit that I'm not entirely certain where this was formally published as it is now in an online open-source repository, www.plosone.org. The authors appear to come from respectable organisations. I sometimes think that peer review is an over-rated idea anyway!