The Rule of 150
A brief introduction into Dunbar’s social hypothesis
Chances are you’re probably somewhat familiar with the “Rule of 150". You perhaps already know that it’s a theory that represents the maximum number of people that we are supposed to able to maintain a social relationship with. I’m certainly no expert, but here are a couple of things that I find interesting about the subject.
How the number 150 was born
Skipping a lot of scientific detail here, but simply put: as members of the primate family we fit into an evolutionary pattern. Our brains are not programmed for us to have more than a very limited number of people in our social circle. Close relationships require significant investment, both emotional and psychological, yet humans are limited in terms of their emotional capital.
The guy who came up with the rule, Robin Dunbar, supposed that primates with bigger brains have bigger social groups. So he compared the size of the neocortex (the layers of neurons on the surface of the brain, where conscious thought takes place) of different types of primates against the size of the group it lived in. He found the correlation he’d been looking for: the bigger the neocortex, the larger the group a primate could handle.
As group size grows, a crazy amount of data must be processed. Imagine a group of five friends. It has a total of 10 bilateral relationships between its members. A group of 20 already has 190; a group of 50, 1,225. Such a social life requires a hell of a lot of brain power. To come up with a predicted human group size, Dunbar plotted our neocortex measurement on his graph and got 147.8. And that’s where the rule of 150 was born.
Examples of the rule in practice
If you look carefully, the rule of 150 pops up more often than you might think.
You may have heard of the rule of 150 in relation to social networks like Facebook or Path. Path uses Dunbar’s thinking as a foundation to try to mirror the social dynamics of the real world.
Research shows that although you may have many connections on Facebook, you only realistically maintain contact with a small proportion of them.
Other studies have found that Twitter users, despite how easy it is to follow and interact with people on the platform, can only realistically manage between one and two hundred stable connections.
In financial planning (and likely other industries where it’s important to work closely with clients), it has been anecdotally suggested that one planner can only handle 100–125 clients at any one time.
Why we should care
Whereas our ancestors knew the same people their entire lives, in today’s increasingly mobile society we move around more, and as a result we lose touch with even our closest friends. Your 150 today might not be the same as your 150 a year ago, nor your 150 a year from now. It’s claimed that emotional closeness can decrease by 15 percent yearly when you don’t maintain face-to-face contact with someone. That means in just five years one of your best friends could find themselves at the most distant outer layer of your 150 social relationships. That’s a scary thought.
