How Understanding Dunbar’s Number Can Help You Build Stronger Relations and Organizations

Dunbar’s Number is a measurement of the cognitive limit to the number of individuals with whom any one person can maintain stable relationships.

Robin Dunbar

Dunbar’s Number is a suggested cognitive limit to the number of people with whom one can maintain stable relationships, in which an individual knows who each person is and how each person relates to every other person. This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. Dunbar’s argument is that brains evolve, and get bigger in order to handle the complexities of larger social groups. If you belong to a group of five people, you have to keep track of ten separate relationships: your relationship with the four others, and the six other two-way relationships between the others. Then, you know everyone in the group. You have to understand the personal dynamics of the group, juggle various personalities, keep people happy, manage the demands on your own time and attention, etc.

When belonging to a group of twenty people, there are 190 two-way relationships to keep track of. Thus, even a relatively small increase in group size, creates a significant additional social and intellectual cost.

By using the average size of the neocortex relative to the size of the brain, Dunbar developed an equation which works for most primates, that outputs the expected maximum group size of the animal. For Homo Sapiens the group estimate is 147.8, roughly 150. In other words, he proposed that humans can comfortably maintain 150 stable and genuine social relationships. One might consider this our cognitive social channel capacity. Basically, in today’s terms, the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to meet them in a bar.

A Few Examples

• Dunbar finds empirical backing for his claim on efficient group size in anthropological literature as for instance 21 different hunter gatherer societies for which there is solid historical evidence, such as
  • Walbiri of Australia
  • Tauade of New Guinea
  • Ammassalik of Greenland
  • Ona of Tierra del Fuego (Argentina and Chile)

• The same pattern holds true for military organizations, as they tend to hold as a rule of thumb that functional fighting units should not exceed 200 men. Dunbar argues that with a larger size you would have to impose complicated hierarchies, rules and regulations as well as formal measures in order to command loyalty and cohesion. However, at or below 150, it is possible to achieve these same goals informally as orders can be implemented and unruly behavior controlled on the basis of personal loyalties and direct person-to-person contacts.
  
• The Hutterites (who sprung out of the same tradition as the Amish and Mennonites) have a strict policy that every time a colony approaches 150, they split it in two and start a new one, as “it seems to be the best and most efficient way to manage a group of people” according to one of the leaders Bill Gross. When the group gets too big (~150), organically there is an internal break-out into two or three groups within the larger group. This is something you would like to prevent, by splitting the group into two before this happens.
  
• Gore Associates (that makes e.g. Gore-Tex fabric and special insulating coatings for computer cables) came to the conclusion, on their own, that they would have maximum 150 employees per plant. This meant that no plant would be larger than 50 000 square feet (4 645 m²), with 150 parking spaces. Typically, when people started parking on the grass, it was time to split up and build another plant.

It turns out that peer pressure is much more powerful than a concept of a boss, as people want to live up to what is expected of them. Thus, above the point of about 150 people, structural impediments begin to emerge and the group is no longer able to agree and act with one voice.

Keep In Mind

• Dunbar’s Number is not a hard limit. It is possible for humans to maintain relationships with more than 150 people, but it becomes increasingly difficult as the number of relationships increases.
  
• Dunbar’s Number is not the same for everyone. It may be higher or lower for people with different personalities, cultures, or levels of social interaction.
  
• Dunbar’s Number is not static. It may change over time, depending on factors such as age, lifestyle, and technology.

Overall

Dunbar’s Number is a useful concept for understanding the limits of human social cognition. It can help us to understand why we have difficulty maintaining large social networks, and why we are more likely to form close relationships with a small number of people.

Bear in mind that it has been criticized by some researchers, who argue that it is too simplistic and does not take into account factors such as culture, personality, and technology. However, it is a useful mental model to have at your disposal, and the concept has successfully been widely applied to better manage people by splitting them into smaller, more autonomous groups, which gives the benefit of close relations and ties, with the additional benefits of scale across all such groups.

For more info on Dunbar’s Number, also see the book The Tipping Point by Malcolm Gladwell.

Video version of this article explaining Dunbar’s Number

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