The lockdowns have curtailed our social lives and limited the number of people we engage with socially, nudging us to think about the quantity and quality of our relationships. Whilst it might sound unromantic to take away the spontaneity and the natural course in which we develop relationships, apparently there is science behind the number and depth of our friendships. Robin Dunbar, an Oxford evolutionary psychologist, who found a correlation between primate brain size and average social group size, established the ‘Dunbar’s number’, a suggested cognitive limit to the number of people with whom one can maintain stable social relationships. He showed that for the human brain that number was around 150. In this interview with The Atlantic, he talks about his new book  “Friends: Understanding the Power of Our Most Important Relationships”, which extends this subject to include some fascinating ideas about our social relationships:
The circles of friendship:
“Dunbar’s number really isn’t a single number. It should be a series of numbers. When collecting data on personal friendships, we asked everybody to list out everybody in their friendship circles, when they last saw them, and how emotionally close they felt to them on a simple numerical scale. Relationships turned out to be highly structured in the sense that people didn’t see or contact everybody in their social network equally. The network was very clumpy.
The distribution of the data formed a series of layers, with each outer layer including everybody in the inner layer. Each layer is three times the size of the layer directly preceding it: 5; 15; 50; 150; 500; 1,500; 5,000.
The innermost layer of 1.5 is [the most intimate]; clearly that has to do with your romantic relationships. The next layer of five is your shoulders-to-cry-on friendships. They are the ones who will drop everything to support us when our world falls apart. The 15 layer includes the previous five, and your core social partners. They are our main social companions, so they provide the context for having fun times. They also provide the main circle for exchange of child care. We trust them enough to leave our children with them. The next layer up, at 50, is your big-weekend-barbecue people. And the 150 layer is your weddings and funerals group who would come to your once-in-a-lifetime event.
The layers come about primarily because the time we have for social interaction is not infinite. You have to decide how to invest that time, bearing in mind that the strength of relationships is directly correlated with how much time and effort we give them.”
As you get older, this number declines:
“Who your friends are changes constantly. You don’t throw away all your friends and start again, but you have this kind of churn going on. When you’re younger, in your late teens and early 20s, the churn rate can be very high indeed. Losing and gaining is largely a consequence of who you’re exposed to. Have you moved away to a new place for school or for a job? Have you just been exposed to a new group of people? That stabilizes by [about] the 30s, in most cases, [when people start having children], because babies are the killer for any kind of social life for everyone. But the number starts to decline into old age—mainly by virtue of progressively losing the outermost layers. It ends up, if you live long enough, with just the innermost layer of 1.5.”
About the seven pillars of friendship:
“The seven pillars are seven dimensions of who you are that form the basis of friendship through homophily, which is the tendency for like to associate with like. “Birds of a feather flock together.” Our friends are very similar to us.”…Among the more predictable pillars, such as sharing the same language, growing up in the same location, and having similar worldviews (moral, religious, and political), I was surprised to find that having the same sense of humor was included. Even more counterintuitively, so was having the same musical taste.”
Friendships require investment of time:
“It takes about 200 hours of investment in the space of a few months to move a stranger into being a good friend. This fits with our data, which suggests that close friends are very expensive in terms of time investment to maintain. I think the figures are a guideline rather than precise. It just means friendships require work.”

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