How big's your social network?

Recently, there have been three ideas entirely new to me that have affected me profoundly. By profoundly I mean that until I happened to read the scholarly papers containing the ideas, I had no conception that such ideas even existed. It was such a shock that I had to stop reading and allow myself a little recovery time before reading on. And each time it happened I thought of John Keats, writing about his first experience of reading Chapman’s Homer:

Then felt I like some watcher of the skies
When a new planet swims into his ken


The most recent ‘planet’ was a 2003 paper by RA Hill and RIM Dunbar published in the journal Human Nature. They discuss the relative volume of the neocortex of the brain compared to the rest of the brain. Yes, I know that doesn’t sound very promising, but wait! All primates, such as humans, have a neocortex, the brain’s most recent addition. The neocortex is responsible for cognitive skills, such as identifying and recognising friends and foes. Now, what Hill and Dunbar did was to measure the share of the volume of the total brain taken up by the neocortex, primate species by primate species. They then looked at the size of the social group maintained by members of each species. The remarkable thing is that there is a direct, linear relationship between neocortex share and size of social group. Less neocortex means fewer friends, or at least people to socialise with.

The linear relationship predicts that the average human would have a social group size of about 150 people. This sounds like a lot of people to me, but then I’m a bit odd and not many people want to be friends with me. Anyway, the researchers then surveyed people in the UK, finding out the size of their social group through their Christmas-card lists. The result: the average Christmas-card list contained 154 names. Isn’t the fact that the predictions matched reality so closely fascinating? Now, one might want to run this particular survey again, and in other cultures perhaps, using something other than a Christmas-card list, perhaps e-mail recipients. That would be interesting in itself.