Long ago, when we lived in small villages, your friends’ friends were generally your friends, and vice-versa, with almost complete overlap, because you likely knew the same people — the small number of people who lived in your village. Chances were that number was 150, because 150, as evolutionary anthropologist Robin Dunbar has argued in a social-brain theory built around this Dunbar number , is how many relationships our big human brains evolved to understand and manage. “We find it,” as Dunbar puts it:

in the typical community size of hunter-gatherer societies, in the average village size in county after county in the Domesday book, as well as in 18th-century England; it is the average parish size among the Hutterites and the Amish (fundamentalist Christians who live a communal life in the Dakotas and Pennsylvania, respectively). It is also the average personal network size – the number of people with whom you have a personalised relationship, one that is reciprocal (I’d be willing to help you out, and I know that you’d help me) as well as having a history (we both know how we came to know each other).

In today’s Guardian, Dunbar considers a key puzzle posed by that theory now that we live not in small villages but in complex societies where social circles don’t overlap as heavily.

In traditional small-scale societies, everyone shares the same 150 friends. This was true even in Europe until well into the 20th century, and probably still is true today of isolated rural communities. You might well fall out with them from time to time, but, like the Hutterites, you are bound together by mutual obligation and densely interwoven relationships. And of these, shared kinship was perhaps the most pervasive and important: offend Jim down the road, and you bring granny down on your back because Jim is her second-cousin-once-removed, and shes got her own sister, Jims grandmother, on to her about it.

In the modern world of economic mobility, this simple balance has upset: we grow up here, go to university there, and move on to several elsewheres in a succession of job moves. The consequence is that our social networks become fragmented and distributed: we end up with small pockets of friends scattered around the country, most of whom dont know each other and, perhaps more importantly, dont know the family part of our networks. You can offend Jim, and almost no one will care. And if they do, you can afford to move on and leave that whole subset of friends behind. Networks are no longer self-policing.

Because modern geographical communities no longer have the social coherence they had up until the 1950s, it is perhaps inevitable that people become less willing to remonstrate with miscreants because others are unlikely to back them up. Bearing these factors in mind, is it any wonder that some inner-city communities fall victim to gang violence? Our real problem for the future is how to overcome this social fragmentation by recreating a sense of community in our increasingly urbanised and mobile world.

It’s a nice point, but it raises another question: If we can handle only 150 substantive relationships, how can we increase and strengthen local connections of the sort Dunbar speaks of here while still maintaining the extra-local connections many of us need to work in an extralocal information economy?

In my own life, many if not most of my most vital social connections — bonds of mutual benefit and regard — are with people outside my local geographic communities. This affects both what I get out of my town and what I put into it (aside from taxes), and limits how many important relationships I have there. Sheer longevity in my little town and compensates somewhat; a book I wrote about the region earned me some cred, and weighing in or helping out with local development, school, or health-care reform issues here and there over the years gives me some pull. But I can’t possibly invest the time to build yet more relationships there and also maintain the relationships outside Montpelier — New York, Boston, London, to say nothing of researchers I talk to elsewhere — that I need to do the work I love. I’d run for city council, for instance, if I thought I had the time; but I don’t because I couldn’t’ do the position justice. Many others are in the same boat.

It’s only one tension between local community health and the global economy, of coures, and I don’t know how to resolve it. I’d love to see Dunbar or someone else address it.

Related:

There’s No Such Thing as Too Many Friends

The Gregarious Brain