Dug Campbell

Dunbar’s Magic Number 150

I came across this tweet from Nick Szabo earlier a few days ago which intrigued me:-

So a bit of digging later and I find out that Dunbar’s number is a suggested limit to the number of people with whom a person can maintain stable social relationships. The concept was developed by British anthropologist Robin Dunbar and, somewhat fittingly, christened by someone on Facebook (according to his TEDx talk).

In essence, you’re unlikely to be able to maintain a social group of more than 150 people. That’s people with whom you have a relationship that involves some element of trust and obligation (as opposed to simply people whose names and faces you’re aware of). Out of that figure, you’ll still only have maybe 3 to 10 ‘close’ friends that you can call up in the middle of the night for help. But the total number of friends is supposedly related to brain size and appears to be a restraint imposed as part of our shared evolutionary inheritance.

Dunbar points out that you need to put in effort (interestingly, that predominantly takes the form of conversation in the case of women but shared activities in the case of men) in order to cultivate those close friendships, with any relationship requiring the passage of time to become stronger.

Anyway, the point here really relates to the development of social networks which we all now use to overlay our physical, face-to-face daily relationships. The theory goes that as humans we’ve been able to cultivate larger groups of friends than primates because of our development of speech which enabled us to communicate with far more widespread collections of people away from our close ‘tribes’.

As you would expect, Dunbar’s research has been looked at very closely by the modern networking giants, such as Facebook. Indeed, Path (the social network that is currently struggling to grow despite significant investment) which has always sought to differentiate itself from Facebook has always been structured on the basis that a user has a fixed limit of 150 friends that he or she can befriend with his or her account as a result of exactly the same principle.

To me, 150 seems a high figure. To many, it will seem too few. I suspect that that’s always going to be the case with an arbitrary figure as an output from research. But to me, it’s particularly interesting to see how this figure has actually been adopted for use elsewhere. Take a look at W.L Gore for example. A company that’s often lauded for its innovation and fantastic employee working environment, they’ve had a rule from the start that requires teams to never grow to a size that’s much greater than the magic 150 that Dunbar’s research suggests is optimal.

For all the technology that we surround ourselves with, and the increasingly efficient tools which we choose to communicate instantaneously, it appears that face-to-face, direct discussion still rules the roost.


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