A shared universe › Blog › What makes a friendship · Español
Nobody becomes a close friend of someone else in one afternoon. It takes time, a good deal more than we usually think, and a certain kind of time too. Two researchers have measured it in different ways, and what they have found helps explain why true friends are few and worth so much.
The British anthropologist Robin Dunbar, of the University of Oxford, is known for a number: 150. In 1992, comparing the relative size of the cerebral cortex with the size of groups in different primates, he calculated that a person can maintain around 150 stable relationships. Over the years, he and his team described how those relationships are arranged, in circles that run from the inside outwards:
Beyond that come acquaintances, about 500, and faces you recognise, about 1,500. Each circle has its own rhythm: according to Dunbar, for the relationship to last, the people in the circle of five usually see each other roughly once a week; those in the circle of fifteen, once a month; and those in the circle of 150, at least once a year.
The number 150 is not an exact law. In 2021, researchers in Stockholm repeated the calculations with other methods and obtained very different figures, with margins so wide that, in their view, it makes no sense to fix a number. Dunbar and his team, for their part, continue to find that structure of a few people very close and many more further away in data of very different kinds.
Dunbar calculates that about 40% of our social time and effort goes to the five closest people, and another 20% to the next ten. That is, 60% is shared among just fifteen people. There is not enough time for more, and that is why close friendships are few.
This lifts a burden of guilt from many people: having few true friends is normal. According to Dunbar, the number of close friends most associated with health and wellbeing is around five. And the quality of those few relationships weighs more than their number, as the Harvard study described in what really makes a good life shows.
Jeffrey Hall, of the University of Kansas, wanted to put a figure on that time. In 2018 he asked 355 adults who had recently moved how many hours they had spent with an acquaintance since the move and what relationship they had with that person. He then followed 112 students starting university for nine weeks.
According to his calculations, it takes about 50 hours together to go from acquaintance to casual friend, about 90 to become a friend and more than 200 for someone to be a close friend. These figures are approximate, drawn from what people remembered, but they give an idea: a close friendship is built from months of shared time.
Not all hours count the same. Hours at work added little; leisure hours, a great deal more: hanging out, joking, doing something together for pleasure. Among the students, too, certain kinds of everyday chat brought people closer. Hall suggested changing the setting: if you like someone at work, suggest something outside it.
Sam Roberts and Robin Dunbar followed for 18 months 25 young English people who were finishing school and leaving for university or work. With family, closeness increased. With friends, on the other hand, it fell. What slowed that cooling was effort: talking more often or doing more things together. In that group, girls benefited above all from the first and boys from the second; with so few people, all that remains is that there is more than one way of looking after a friendship.
According to Dunbar, when two friends stop seeing each other, closeness drops measurably within a few months, although it probably takes about three years without contact for someone in the close circles to drop out of those 150 altogether. Messages help the cooling to be slower, but in the long run true friendships need to meet in person from time to time.
Long friendships have something that cannot be improvised: a shared history. Someone who has known you for thirty years knows where you come from without your explaining it. Looking after them does not call for grand gestures:
As an adult, making new friends is harder, and it is not your fault: work, family and tiredness leave few free hours, and a friendship needs many. That is why activities that repeat every week with the same people help, such as a group, a class or volunteering: the hours add up almost without your noticing.
If the lack of company weighs on you, there are more ideas in unwanted loneliness.
That friend who is still there after so many years deserves a few words. You can leave them on a “For someone” star with “What I’m grateful for”. And afterwards, ring them for that coffee you have been putting off for so long.