Dunbar's Number

You can feel it starting to happen again. The name is something really common.. Sandra? Susan?

Does it start with an S at all? Sharon?

You’ve seen this face before, but you can’t quite put your finger on who it is, or who they are to you.

Running into someone “in the wild”, without context, does this to me from time to time. I will see someone and recognize their face, but that’s just about all the information I have on that person at the moment.

In 1993, Robin Dunbar set out to explain why.

Dunbar's number is a theoretical cognitive limit to the number of people with whom one can maintain stable social relationships. These are relationships in which an individual knows each person and how each person relates to every other person.

That number is 150, according to Dunbar's theory.

On a personal level, this number really checks out! At Revolution BJJ, we have somewhere around 410 students right now. I remember a time when I knew everyone’s name in the gym, when it was essentially a given that you’d learn a new name every week or so, one at a time. At some point, probably around at 150 mark, it became much tougher to remember names.

This image represents maybe a fifth of the students, give or take (plus a few guests):

Do you think you could keep track of five times this many faces?

Back over to Dunbar and his revolutionary concept. As a biological anthropologist specializing in primate behavior, he found a correlation between the size of a primate's neocortex and the size of their social groups.

Gorillas have a very small neocortex relative to their brain size, and as a result (or so Dunbar postulated), they hang out in small groups of five to ten individuals. Moving up the primate ladder, chimpanzees often have larger groups of somewhere between 20 and 50 individuals, and their neocortex takes up more space.

Baboons have a neocortex that takes up a ton of space (relative to gorillas or chimps, anyway). They can run in crews as large as 100.

Extrapolating this relationship to humans, he proposed the number 150.

Now, I’m not sure how much stock to put into the relationship between neocortex size and the number of people we can remember and know well. That’s a debate for people far more qualified than me, but the one thing I know for sure is that this framework is useful.

I also know that Dunbar never meant for the 150 number to be exact, so it’s much more of an estimate. Nevertheless, the idea that there’s a limit to the number of meaningful connections and friendships one can sustain really resonates.

If you want to think more about this concept, I wrote about one of the most isolated groups of people, and how Dunbar’s Number applies to them:

Think about your own little social world. How many names and faces do you keep track of? How many people do you really know?