Back in the 1990s, British anthropologist Robin Dunbar hypothesized that the number of significant relationships a human can have is limited by the size of their brain. By plotting the correlation between the size of human brains and the social groups they formed, he predicted that the maximum number of people in someone’s social circle is 150.
Bill Gore, the founder of of a company called GORE-TEX, found that the larger his company grew, the less likely people were to work hard and cooperate with each other. With more than 150 people in the same building, people were unable to keep track of one another, and all sense of community was lost. By building new factories and thus reducing the number of people assigned to each factory to 150, Gore found the sense of community in his company renewed as business skyrocketed.
From GORE-TEX’s model, Dunbar’s number, or the idea that humans can only have about 150 meaningful relationships in their lives, was conceived. Just as we can’t breathe underwater or see microwaves with the naked eye, we can’t maintain more than 150 meaningful relationships at any given time, since we’re cognitively not built for it. This magical number dates back to our primitive origins — in smaller groups, primates could work together to solve problems and evade predators. Further along in history, hunter-gatherer communities numbered at around 150.
“The figure of 150 seems to represent the maximum number of individuals with whom we can have a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us,” Dunbar said, according to Bloomberg. “Putting it another way, 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.”
To conduct this study, Dunbar and his fellow researchers gathered information from public records on about six billion cell phone calls made by 35 people in Europe back in 2007 to see who was talking to whom and how often. The results showed that about 27,000 people called 130 other people on average and made about 10 calls per day.
Rather than a single number, Dunbar’s number is a series with 150 being the most widely known, according to Technology Review. The number actually increases and decreases over a range of layers based on emotional ties. The closest layer consists of five people who can be considered our closest friends. Next is fifteen close friends, then 35 close acquaintances and finally 100 acquaintances, adding up to 150 people total.
According to The New Yorker, the absolute limit of this series is 500, indicating the number of people for whom you can put a name to a face. These group sizes are relatively stable, but their composition is fluid — the five you consider your best friends today may not be in the same layer next week, and people can shift between layers or even fall out of them altogether.
There’s also the question of how Dunbar’s number factors into advances in online social networks. According to Bloomberg, software engineers at Facebook and startups like Asana and Path invoke Dunbar’s number to replicate and enhance face-to-face communication.
“What Dunbar’s research represents is that no matter how the march of technology goes on, fundamentally we’re all human, and being human has limits,” said Path Co-Founder Dave Morin. “The question is, ‘Does digital technology in general allow you to retain the old friends as well as the new ones, and therefore increase the size of your social circle?’ The answer seems to be a resounding no, at least for the moment.”