Dunbar's Number Explained Simply

Dunbar’s Number – All You Need To Know

In this post, we’ll unpack all you need to know about Dunbar’s Number, defining exactly what it is, its origin, how it relates across cultures, the science behind it, why it matters and more.

What Is Dunbar’s Number?

Named after British Anthropologist Robin Dunbar, Dunbar’s Number refers to the theoretical numerical limit of people that one can maintain stable relationships with.

While an individual’s social network may contain more, 150 marks the cognitive limit on those with whom we can maintain a stable social relationship involving trust and obligation. Move beyond 150 and people are mere acquaintances.

The Origin Of Dunbar’s Number

The number 150 was first proposed when Dunbar found a correlation between primate brain size and average social group size. He went on to theorise that the limit of relationships we can maintain is a direct function of the limit imposed by neocortical processing capacity.

By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships. In this context, “stable relationships” are relationships in which an individual knows who each person is and how each person relates to every other person.

Dunbar’s Number Across Cultures

Combing through the anthropological literature, Dunbar found that the number 150 popped up again and again across many different cultures.

For example, he analysed 21 different hunter-gatherer societies with solid historical evidence. He found that the average number of people in their villages was 148.4.

The same pattern holds true in many other cultures. This includes the average size of historical English villages, the ideal size for church parishes and the size of businesses.

Why It Matters

Dunbar’s Number implies that there is an upper limit on the size of any group that can work effectively together.

Once a group expands beyond 150 people, then it’s impossible for everyone to know everyone else. Individual relationships break down. Since people don’t know each other in large groups, the usual methods of maintaining social relationships don’t work. Thus, new mechanisms are required to help maintain stable and cohesive groups.

Summary (TL;DR)

Dunbar’s Number refers to the theoretical number of stable relationships that humans can maintain.

If the number of 150 relationships that we can maintain is accurate, we can use this information to maintain group cohesion.


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