Dunbar’s Number

In the 1990s British anthropologist Robin Dunbar performed an interesting research and suggested that humans can comfortably maintain about 150 contacts. It’s now best known as the Dunbar’s Number and it’s a measurement of the “cognitive limit to the number of individuals with whom any one person can maintain stable relationships”. Stable relationships mean that you know who they are and how they relate to you – as Dunbar explained “it’s the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar”.

Based on Dunbar’s research and social brain theory it’s suggested that the average person’s relationships are grouped in 6 layers (or circles, if you will) of social proximity, and it seems to follow a simple pattern – at each level the size of the layer (number of people/relationships) typically increases by a factor of 3. The numbers are:

• Close friends (5 people)
• Good friends (15 people)
• Close network (50 people)
• Personal network (150 people) – Dunbar’s Number
• Acquaintances (500 people) – These are people we have contact with, but the additional 350 people are not part of your core network and you don’t know much about them
• Recognizable (1500 people) – You recognize the faces, but these are people with whom you don’t have a great deal of social contact

Dunbar’s findings affect not only our personal lives, but also how we interact at work and how we maintain our business relationships. It basically means that there are limits to number of people that should be on one team, number of people that should belong to a department (~50) or to a division (~1500). There are organization that take social brain theory seriously and shape their structures accordingly. Unfortunately, many leaders ignore these facts and expect results that are impossible to achieve. I.e. “a team” of 100 people is expected to “work closely together on daily basis” or, my favorite, a group of 250 people is expected to “break down the silos and act as one team” to streamline the communication and knowledge sharing.

We need to understand that we have our cognitive limits. Like it or not, but maintaining meaningful relationships require time and effort. This inevitably means we can’t have an unlimited number of meaningful relationships and we should optimize how we spent our cognitive fuel each day. And organizations should be structured in a way that recognizes these limits and supports the most effective relationships and communication flows.