Dunbar’s number revisited

A while back, I made a brief reference to the so-called Dunbar number in relation to my list of friends on Facebook.

Since then, I’ve spent some time reading up on Dunbar’s number and the concept of friends on social networking sites, and feel the need to delve deeper into this discussion. danah boyd, one of the leading researchers on Social Networking Sites, has made the point that

Friends lists are not an accurate portrayal of who people know now, who they could ask favors of, who they would feel comfortable introducing at the moment. They’re a weird product of people from the past, people from the present, people unknown, people once met.

Based on my own anecdotal evidence, I find this to be exactly right. I have loads of contacts on Facebook that I haven’t seen, nor kept in touch with in ages, only now I have a sort of ambient awareness of what is happening in their lives. It’s like having a auto-updating version of the various social spheres I happen to be in. I guess the most apt metaphor would be a college yearbook – the original facebook – that updates itself everyday.

So, how does this relate to Dunbar’s number? Well, Robin Dunbar is an anthropologist who hypothesized that “there is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, that this limit is a direct function of relative neocortex size, and that this in turn limits group size … the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained.”

Dunbar sought to prove this hypothesis by correlating a number of studies measuring the group size of a variety of different primates with the brain sizes of the primates. He used these correlations to produce a mathematical formula for how the two correspond. Using his formula, which is based on 36 primates, he found that 147.8 is the “mean group size” for humans, which he found to match census data on various village and tribe sizes in many cultures.

So that’s the basis of the Dunbar’s number of 150 relationships. But as Christopher Allen has done well to point out, reducing Dunbar’s research to just one number would be misleading. As he concludes: The “Dunbar’s group threshold of 150 applies more to groups that are highly incentivized and relatively exclusive and whose goal is survival.”

Similarly, boyd sums up Dunbar’s point quite well:

Just as monkeys groomed to maintain their networks, humans gossiped to maintain theirs! He found that the MAXIMUM number of people that a person could keep up with socially at any given time, gossip maintenance, was 150. This doesn’t mean that people don’t have 150 people in their social network, but that they only keep tabs on 150 people max at any given point.

But one thing is how many active social relationships we can have – i.e. how many people we can keep up with socially in a reciprocal fashion. Another thing is how we know these people and how well we know them. Our social relationships come with both a context and a strength of your shared bond. The context and the strength of our relations is crucial for how we distribute information, support, and trust among our friends.

Typically, we can group our relations in various groups based on the context of the relation: People we know from work, from school, from hockey practice, or people we know through our significant other, people we’ve been introduced to by another relation. Until social networks like Facebook came along, these groups rarely overlapped and got a chance to meet. But these social networks suddenly expose more about our contextual relationships to different groups of people than we would ever do in real life, and we end up having to reconcile the bar-hopping facet of our identity with the paid work facet.

Clay Shirky does well to analyse the consequences of this new social situations. As he argues: It’s not information overload. It’s filter failure: All of the sudden people are able to discover new social contexts in which their friends are part because the filters, which people had in place are no longer working:

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