This number was predicted by an evolutionary psychologist, Robin Dunbar, at the University College London in the 90's. He noticed that a given species of primates always formed groups no larger than a certain size and, more intimately, that a member of a group always had about the same number of grooming partners. For example, chimpanzee tribes number about 50 and each chimp has no more than 2 or 3 grooming partners.
He proposed that the maximum group size for a primate species depends on the size of the primate's neocortex. Extrapolating to humans, he derived the theoretical group size of 148, noting that this limit seems to be reinforced by the size of various human social organizations including Neolithic villages, Hutterite communities and army units.
He also noted that rather than "physically grooming", humans are able to substitute language as the key way for humans to maintain personal contact. He speculates that as much of 42% of a group's time would have to be devoted to social grooming/interaction to maintain group cohesion.
You can read Dunbar's document here.
This concept was then popularized in Malcolm Gladwell's book, "The Tipping Point: How Little Things Can Make a Big Difference. " In this book, he shows how ideas and message and behaviors can become mainstream when even a small number of people start behaving differently, an appealing concept to a marketer. He points to the Dunbar number group size as foundational in organizing marketing campaigns.
Two other anthropologists, H. Russell Bernard and Peter Kilworth, have led field studies directly focused on modern society and have found a repeated finding roughly double the Dunbar estimate (a mean number of 290, a median of 231).
Now, with new Social Media mechanisms like Facebook, LinkedIn and Twitter humans have new and efficient ways to establish social groups. Do these in practice reflect the hypothetical limits that the scientists suggest? Or do the social media mechanisms enable a greater effective social group due to more efficient methods of "grooming?" Or do they enable more gradients of "grooming and quality of relationship?" How can marketers harness this?At this point I see three directions:
- People will continue to have the same size small set of intimate friends they had before Social Media. Social Media will enhance those relationships.
- People will maintain ongoing casual relationships with a larger sphere of people, likely in the range of the Dunbar number for the more socially active. This sphere will be of people they actually know. These groups may be somewhat larger than "before Social Media" due to the efficiency and nature of the communication mechanisms.
- Social Media mechanisms will allow people who offer value much vaster circles of influence than ever possible before.
Here's data from a Facebook case study from The Economist which reinforces the first two points:
- The average number of Facebook friends in a network is 120 with women having somewhat more than men. However, the number with which an individual regularly interacts is much smaller than their network. The average man has regular two way communication with only 4 friends, the average woman with 6. These numbers don't increase much (10 and 16, respectively) for those with large networks, 500+.
This third point has been amply demonstrated with Twitter where top influencers directly reach hundreds of thousands of people who have chosen to follow them (e.g. Guy Kawasaki, Ashton Kutcher). Their tweets are then retweeted which increases the effective reach. Most importantly, there is value and real influence in the content.
So I believe Social Media has changed the nature of social groups and grooming. There is no longer one Dunbar number. As marketers, we need to keep abreast of the newly evolving social break points that Social Media mechanisms enable and harness them in our marketing efforts. We have unprecedented opportunities to find fans and influencers and have messages spread faster, more quickly and more efficiently than ever before.
