Scotland Street Volume 18, Chapter 2: The categories of friendship

‘Robin Dunbar,” said Angus. “I’m reading his book. You’ve seen it. It’s the one Matthew lent me. He got it from Big Lou. He’s an evolutionary psychologist. It says that on the back cover. Do you know what that is?”
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Domenica knew. She was an anthropologist; evolutionary anthropology was an important branch of her own discipline and took much the same approach. “Evolutionary psychology,” she explained, “looks at how our behaviour and dispositions have been moulded by our survival instincts. If we do something, it’s because it helped evolutionary survival.”

She hoped she did not sound too pedantic. It was sometimes difficult to deal with complex ideas without sounding as if one was delivering a lecture, but it was hard to see how one could otherwise describe evolutionary psychology. It was like trying to illustrate the double helix without using one’s hands.

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But Angus understood. “That’s why he spends so much time studying friendship. Is it all to do with survival?”

Domenica nodded. “Ultimately, everything’s to do with survival if you’re an evolutionary psychologist – friendship’s no exception. I haven’t read him on the subject, but I imagine your Professor Dunbar says that the reason we have friends is that if we don’t, we perish.”

“Yes,” said Angus. “I think that’s his approach. I’m only on chapter four, though.”

“And his number?”

“The Dunbar Number,” Angus said, “is 150.”

Domenica smiled. “We’re always keen to find a number that explains everything,” she said. “What’s the number in The Hitchhiker’s Guide to the Galaxy that explains everything? Forty-two, I seem to recall. That’s the answer to the question, although nobody actually remembers what the question was.”

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Angus brought up the Golden Ratio. That was his number, he felt. Other people could have 42 or 150: he would stick to 1.618, or phi. “I’ve always believed in phi,” he said. “One of our tutors at art college swore by it. He told us that if we wanted to understand beauty, we had to be able to detect phi in whatever it was we were looking at. A beguiling face. A shell we’ve picked up on the beach. An example of Palladian architecture.” He paused, and gestured towards the window. “That window. The ratio between its height and width is phi. 1:1.618.Much of the Edinburgh New Town is the embodiment of that ratio. Phi is ubiquitous.”

“All very interesting,” said Domenica. She and Angus had discussed phi before; you could not be married to a person for long before discovering their views of phi. “But why 150?”

“That’s the number of friends we can have,” said Angus. “Not close friends, of course – we have far fewer of those – but friends we’d actually describe as friends rather than –”

“Acquaintances?” suggested Domenica.

“Yes.”

Acquaintance was a rather cold term, thought Domenica. To call somebody a mere acquaintance implied that it was unlikely that they could be something closer – that they would remain something barely above stranger. It was preferable, though, to the term she had heard one of the students in the downstairs flat using: randoms. That suggested a profound separation – even an indifference. Some terms were destined, she thought, to remain the property of the young – and random, in that sense at least, was one of them. These were words that wore their baseball caps backwards. Not, she thought, with an inner grin, that I am in any way hostile to neologisms …

“How did Professor Dunbar arrive at 150?” she asked.

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“Because it’s always been there,” Angus replied. “If you look at the size of human communities – in all sorts of societies – historically the basic unit was around 150. For a very long time, there were about 150 people in villages. When the population became bigger, new settlements were created. And plenty of other human associations recognise this. Companies do. Armies too. They organise themselves administratively in collections of about that number of people.”

“But why?”

Angus smiled. “Try talking to more than 150 people.”

Domenica looked thoughtful. “Yes, I can see that. You won’t know the people you’re talking to if there are –”

Angus completed the sentence: “Too many of them. We only trust people we know – or people we feel we could get to know. One hundred and fifty, it seems, is a natural size for a human community.”

“Big groups then –” Domenica began.

“Don’t work,” Angus interjected. “People are unhappy in big groups.”

“Nations?”

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Angus hesitated. Then he said, “They work best if they’re small: Singapore, Switzerland, Denmark. You do know, by the way, that the Danes are the happiest people in the world. Empires are inherently unstable. States that are made up of reasonably manageably-sized units are less shaky.” He closed his eyes for a moment. He wished the world at present was just a little less shaky … He continued, “But what really counts is being part of something much smaller. That’s why people in large cities create villages within the metropolis. Then they tell others, rather proudly, that their city is made up of villages.” Angus paused. “But I shouldn’t be telling you this. You’re the anthropologist, not me.”

Domenica smiled. “I knew it, I suppose. But you’re the one reading the book – obviously. I’d heard of Professor Dunbar, though. Doesn’t he have other numbers?”

“Yes,” replied Angus. “There’s 1.5. We have 1.5 intimates. Then there’s five. That’s the number of close friends we can manage. After that, it’s 15, which is the number of best friends we have – followed by 50 good friends.”

Domenica was silent. She was thinking of best friends – and of the letters she had to write, if she was to keep her friendships in good repair, as we were advised to do. And, as it happens, so was Angus.

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He thought of his friends from art college – they were good friends on the Dunbar scale. They had been through so much together, and yet he only saw one of them now. And his friends from the Scottish Arts Club. He had let so many of them slip away, as one does, simply by forgetting, or by not doing what he and Domenica clearly should do, which was to invite them round for a meal. Break bread with those you loved – you had to do that, and yet we did not do it enough because …why? Because of the pace of the life we led now: with all the things we had to do; with all the information we had to absorb; with all the moments we lost when we might otherwise think of our friends, or sit with them and hear them say the things they always said and that we had heard them say so many times before.

© Alexander McCall Smith, 2025. Bertie’s Theory of Ice Cream will be published by Polygon in August, price £17.99. The author welcomes comment from readers and can be contacted at [email protected]

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