Dunbar's number is the theoretical number of people with whom one can maintain meaningful and stable social relationships.
The concept was proposed by British anthropologist Robin Dunbar in the 1990s.
It started with his research into feral goats in Scotland. Then he moved on to chimpanzees and other primates, looking at why they groomed each other. Was it for reasons of hygiene, or to become friends? Dunbar said: “I found a very nice relationship between brain size and grooming group size. If humans were like primates, the size of our social groups should be limited by the size of our brains.”
He went on to observe 38 types of non-human primates in an attempt to predict an optimum social group size for humans, by taking into account the relative sizes of the neocortex in their brains.
Dunbar predicted a human "mean group size" of 150 suggesting that humans can comfortably maintain, on average, that number of meaningful relationships. These relationships are not just acquaintances but involve knowing who each person is and how each person relates to every other person within the group. Dunbar explained the principle 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” or “the people you know well enough to greet without feeling awkward if you ran into them in an airport lounge”.
According to Dunbar and the many researchers he influenced, this rule of 150 remains true for early hunter-gatherer societies as well as a surprising array of modern groupings: offices, communes, factories, residential campsites, military organisations, 11th Century English villages, even Christmas card lists.
Exceed 150, and a network is unlikely to last long or stay cohesive.
In a piece he wrote for the Financial Times on 10 August 2018 called “Why drink is the secret to humanity’s success” about the positive role that the moderate intake of alcohol has played in the socialisation process over the years, Dunbar mentioned two more numbers: an inner core of about five people to whom we devote about 40 percent of our available social time, and 10 additional people to whom we typically devote another 20 percent.
All in all, we devote about two-thirds of our time to just 15 people.
So, looking at the diagram, and according to this theory, the tightest circle around us contains just five people – loved ones. That’s followed by successive layers of 15 (good friends), 50 (friends), 150 (meaningful contacts), 500 (acquaintances) and 1500 (people you can recognise). People migrate in and out of these layers, but the idea is that space has to be carved out for any new entrants.
Having said all this, social media and technologies are being designed to encourage us to grow our networks to seemingly unsustainable levels … to much higher numbers than those referenced above.
But fear not for Dunbar’s legacy. Further research has found that the relevance of Dunbar’s number is not impacted by social media metrics. As we’re sure you’re aware, your so-called Facebook “friends” are not necessarily your friends.
Story Idea: Claire Hanley
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References
wikipedia.org/wiki/Dunbar's_number
sciencedirect.com/science/article/abs/pii/004724849290081J
ft.com/content/c5ce0834-9a64-11e8-9702-5946bae86e6d
bbc.com/future/article/20191001-dunbars-number-why-we-can-only-maintain-150-relationships
themarginalian.org/2016/08/16/friendship
christopherroosen.com/blog/2019/4/26/relationships-are-a-limited-numbers-game
Images
1. Dunbar Doodle. Credit: Remo Giuffré.
2. Robin Dunbar. Photo credit: Magdalen College, University of Oxford
3. Primate friends grooming. Photo credit: Blickwinkel.
4. Social networks
5. Group of friends drinking beer. Photo credit: Pavel Danilyuk.
6. Book: How many friends does one person need? Robin Dunbar, 2010
