Prof Robin Dunbar: How many friends do you really need?

From Saturday Morning, 9:30 am on 25 January 2020

Could having too many friends be bad for you? The answer is yes, according to Oxford University Professor Robin Dunbar who studies human social networks.

Maintaining a friendship is cognitively demanding and our brains may be wired with a limit to the number of stable social relationships we can handle.

Dunbar started his career studying African monkeys before turning his attention to less hairy hominids.

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Photo: Photo by Duy Pham on Unsplash

His key discovery? That a primate's brain size seems to dictate the size of their social networks and the number of relationships they can maintain. That number is 150.

He tells Kim Hill that number – now called the Dunbar number – was a predication based on an equation that related social group size in monkeys and apes to their brain size.

“Probably for the only time in my life, ever, I made a prediction and it turned out to be right.”

They know it to be right because studies of hunter-gatherer groups around the world tended to form communities that ranged from size between 100-200 people. Furthermore, when they asked people to list all the people they had contacted in the previous year, not including financial chores or obligations, it averaged 150.

Prof Dunbar says the limiting factor of our social group size is down to two things.

“Firstly, our brain. The principle is, how many relationships can you handle at any one time. We’ve been able to show with brain scanning experiments that the number of friends you have correlates with a particular neural circuit in the brain.

“In addition to that, there’s an issue about time because what keeps relationships, particularly friendships, going is how much time you invest in them. It turns out we allocate our time across our various friendships and family relationships in quite specific ways and, eventually, you just run out of time.”

He says the difference between extroverts and introverts relates to the amount of casual friendships one has, but the biggest difference is the amount of time and effort they put into relationships.

“Introverts prefer to go for having a few friends and investing a lot of time in each one, so the friendships are very strong. Extroverts, taking the same amount of time, spread it more thinly among more people, so their relationships are more fragile in a way.”

Another way we diverge in our relationships is between males and females. Prof Dunbar says friendship is more important to women than it is to men, and women are much more likely to have strong friendships with other women that pass the test of time.

“My cartoon version of this is how life was like at 9 or 10. For girls, if Penelope doesn’t invite you to her party, it’s the end of the universe as we know it. These friendships are very intense and very one-to-one. Whereas, for boys, they’re sort of standing on the opposite side of the road kicking a football back and forth.

“I maintain that, for a little boy or even a big boy, as long as the ball comes back – that’s a friendship. It doesn’t matter if it’s the wall the sends the ball back or another little boy, that’s a friendship.”

Prof Dunbar says that because humans, unlike monkeys and apes, find grooming too intimate to do to people unless they’re in relationships or at least very intimate, we’ve developed things like church, song, and dance that bring us closer together while having less intimate touch.

“When our ancestors needed to live in bigger groups, pushing up towards this 150 figure, they need to find other ways of triggering the endorphin system. That’s the only way you can, in effect, groom several individuals at the same time.”