Dunbar’s Number Explained

Dunbar's Number

Introduction: What is Dunbar’s Number?

In the ever-evolving era of social media and human interactions, what if someone asks you how many friends do you have? What would be your answer? 5? 50? 150? Equal to the number of your Instagram followers or Facebook friends? What if you were told that there is an actual limit to the number of friends you can have and people you can maintain stable social relationships with? Surprised? “150” or the Dunbar’s number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships in which an individual knows who each person is and how each person relates to every other person.

History and Discovery

This number was first proposed in the 1990s by British anthropologist Professor Robin Dunbar, who found a correlation between primate brain size and average social group size. This correlation was simple: the bigger their brains, the larger their social groups. The explanation made sense as bigger the brains of the animal, larger is its capacity to remember and thus can interact with more of their peers meaningfully.

He plotted this correlation and extrapolated it to the size of the human brain and thus predicted that humans cannot have more than 150 people approximately in his social sphere.

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Photographer: Agence Olloweb | Source: Unsplash

He does not say that the limit has to be exactly 150 though. According to Dunbar, the number can vary due to gender, social exposure and identity. Dunbar explained it informally as “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.” Throughout history, these are a few examples which validated Dunbar’s theory:·

· A study of the 20 tribal societies with available data showed a mean clan group size of 153

· Surprisingly the average number of Facebook friends is 150–200

· A 2011 twitter study of 1.7 million users found they, maintain a stable relationship with 100–200 individuals

· Exchange of Christmas cards in the UK and the maximum network size was about 153.5

· 2008 survey by The Knot Wedding Network of over 18000 brides revealed an average wedding guest total of 148

· The Roman army during the Republic utilized a fighting unit called the Maniple with 130–140 solders & officers

· When an NFL team wins the super bowl, 150 rings are awarded

· Modern military companies top at about 150

· Middle Eastern Neolithic villages dating back to 6000BC usually populated 120–150

· The Doomsday book written in 1086 on surveys by the conqueror king William which is one of the oldest ever reports about population, reveals an estimated English village size around 150

· Even in the 1800s, an average English village had about 160 residents

· Today the Hutterites, and Amish communities split groups if they exceed 150

· Bill gore split his Gore-Tex factories by 150 to keep his employees functioning in personal cooperative relationships.

Reasons for this limitation

1. Cognitive limitation

Medical information exhibit at the Museum of Weed
Photographer: Bret Kavanaugh | Source: Unsplash

The human brain is one of the most advanced and complex amongst all the other animals yet it has its limitations. The number of social relationships which the human brain can uphold is limited. Dunbar explains: “this limit is a direct function of relative neocortex size, and that this in turn limits group size, the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained”.

The neocortex is the part of the brain responsible for sensory perception, cognition and language. The connection between neocortex size and a number of social relationships was then established after several experiments and research. In simple words: bigger the brain, bigger the social circle.

2. Time limitation

Eventually everything hits the bottom, and all you have to do is wait until someone comes along, and turns it back again. ⌛️
Photographer: Aron Visuals | Source: Unsplash

Maintaining social relationships requires commitment and consumes a substantial amount of time. Having an unusually big social circle hampers productivity and also becomes incredibly tough to maintain due to time limitation.

The Social Media Factor

Social Media Facebook
Photographer: William Iven | Source: Unsplash

Dunbar and his team have also performed research on Facebook, using factors such as the number of groups in common and private messages sent to map the number of ties against the strength of those ties. When people have more than 150 friends on Facebook or 150 followers on Twitter, Dunbar argues, these represent the normal outer layer of contacts or the low-stake connections—be it 500,1,000 or 1,500.

For most people, intimacy may just not be possible beyond 150 connections. In his opinion, various digital media are really just providing us with another mechanism for contacting acquaintances. Dunbar says that there is a consistent pattern, and it scales roughly by a factor of three each time—five intimate friends, 15 good friends,50 close friends, and 150 friends. He also supposes that the numbers continue beyond that—500 acquaintances and 1,500 people who you could put a name to a face.

Even the possibility of anonymity online doesn’t seem to Dunbar to be substantially different from the offline world. He compares anonymous internet interactions to the use of confessionals in the Catholic church.


It makes sense that there is a finite number of friends most individuals can have. What is less clear is whether that capacity is being expanded, or contracted, by the ever-shifting ways people interact online. Isn’t it hard to cry on a virtual shoulder? Can you compare an online conversation to the personal meeting? Does that give that closeness feeling? “Virtual friendship does not last, it is literally fragile.” Dunbar quotes. However, Dunbar’s own research suggests generational differences in this regard. Those aged 18–24 have much larger online social networks than those aged 55 and above.

Moreover, the primacy of physical contact in the social brain hypothesis may apply less to young people who have never known life without the internet, for whom digital relationships may be just as meaningful as analogue ones. No one really knows how relevant the Dunbar number will remain in a world increasingly dominated by virtual interactions. Well, only time will tell who your true friends are who love you for you and are not just another acquaintance on a social media platform. Whether the Dunbar number will shrink or rise, that is a mystery of its own.