The More Friends You Have, the Longer You're Likely to Live

People living in virtually every culture, and throughout history, typically have an average of 150 friends, says Robin Dunbar, an evolutionary psychologist who's spent decades studying primate and human relationships. His new book analyzes how social ties affect our quality of life in unexpected ways

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Groups of people the banks of the Seine in Paris.
For women, friendship is all about the conversation. For men it's about doing things together. Credit: FRANCOIS GUILLOT / AFP
Tzach Yoked
Tzach Yoked
Tzach Yoked
Tzach Yoked

Here’s an interesting experiment for anyone who’s curious and has some spare time. Take a pen and paper, or use your computer, and make a list of your friends – counting those who you see as being very close to you and also those who are less close. Or you can skip the list and rely on the research of Prof. Robin Dunbar, the noted British anthropologist and evolutionary psychologist, who has found that every person has an average of 150 friends. “Dunbar’s number,” as it has been dubbed – that is, the number of people an individual has the cognitive capabilities to maintain as friends – and has been known in academic circles for the past 30 years.

Dunbar, 74, heads a group of Oxford University researchers that studies the connection between cognitive phenomena and social and evolutionary processes among primates and humans, and he has devoted his professional life to the study of friendship. What exactly does that concept mean? What are the conditions that make possible the formation of a meaningful friendship? And what is the dramatic role that friendship plays in our life?

In Dunbar’s latest book, “Friends: Understanding the Power of Our Most Important Relationships,” he presents in depth the insights he has gained over decades of research. The book integrates the results of many scientific studies and the personal experiences of researchers including himself with input from the realms of anthropology, cognitive sciences and genetics.

It turns out, for example, that it’s possible to break down into hours the length of time it takes for a stranger to be transformed into a true friend. In practice, “240 hours of personal contact, face to face, are required to turn a complete stranger into a good friend,” Dunbar says, in a Zoom conversation from his home in England. If so, how do people decide in whom to invest that much time?

According to Dunbar, there are seven fixed criteria that help predict who will become part of our circle of friends. Some are obvious: Most of our friends tend to be people who share our language and have similar geographical roots, educational level, spheres of interest and worldviews. But no less important, it emerges, is for friends to share our taste in music and sense of humor. These traits constitute “the collection of beliefs that define the community to which I belong,” the professor explains.

His new book is studded with fascinating observations (for example, he claims that when we get married we lose two friends on average – a subject we’ll get back to), but the connecting thread running through it is the powerful connection between social ties and a person’s quality of life, health and even longevity.

“The evidence indicates that the more friends we have, the less likely we are to fall ill, while our lifespan increases,” Dunbar explains.

For example, he cites in his book a study conducted about a decade ago by researchers at Brigham Young University in Utah and the University of North Carolina at Chapel Hill – based on data from about 300,000 people in developed countries – that found that individuals with a large web of social ties have a 50-percent greater likelihood of surviving a heart attack or a stroke, as compared with people who have a limited social circle. In another study, some of the same scholars found that among solitary individuals aged 60, the probability of death is 30 percent higher than among those with more extensive social ties.

A pair of researchers from University College London who examined data for 6,500 British citizens in their 50s came up with similar findings, in 2012. Their study, which examined the impact of social isolation over a decade, found that loneliness heightens the likelihood of death by no less than 25 percent. A subsequent and surprising study that Dunbar quotes detected a connection between the sociability of 6-year-olds and high blood pressure and obesity among the same sample when they are in their 30s: That is, boys who spent more time with friends were less likely to suffer from those medical conditions. In addition, researchers at Carnegie Mellon University in Pittsburgh found a connection between social ties and the body’s immune system: A flu vaccine administered to thousands of students was far less effective among those who reported feeling lonely.

“In other words,” Dunbar says, “the students who reported a feeling of loneliness had far lower immunity to the virus. The stronger the sense of loneliness, the less effect the vaccine had.”

Dunbar. “The social circle is fluid; we lose friends and acquire new friends all the time. In the 18- to 19-year-old age group, that occurs very frequently. It happens in mid-life, at a far slower pacCredit: Andre Camara

How do you explain the connection between social ties and health?

Dunbar: “I don’t explain it, and nobody can yet. But it is a very robust effect, widely evidenced in many different studies. There are two likely routes, however, both acting through the effect of friends on the endorphin system [a reference to the neurotransmitters that act to increase feelings of pleasure and well-being, and also to reduce pain and discomfort]. One is the direct effect endorphins have as opioids. They lift your mood and dull the pains that you have [by elevating pain thresholds]. That prevents you from sinking into a downward spiral of despondency, which is well known to adversely affect both psychological and physical health. In addition, it seems that endorphins activate the immune system. The endorphins seem especially to trigger the release of the immune system’s NT [so-called “natural killer”] cells, which target viruses and some cancer cells.”

Perhaps the effects are due to the fact that social individuals are also more active physically?

“These factors have all been taken into account in the studies that have looked at this. Yes, lack of exercise has an effect, but lack of friends has an even greater effect on top of this.”

Concentric circles

“The evidence indicates that the more friends we have, the less likely we are to fall ill, while our lifespan increases,” Dunbar explains.

All this begs the question of how one defines friendship – by nature, a term that has a different meaning for each individual and every culture. Dunbar defines the concept as based on the frequency with which one expends an effort to make contact with a particular person. The “seam line,” as he calls it, is one year: “In other words, if a year has passed and you didn’t bother to make contact with a particular individual, you are probably not truly friends.”

An additional measure, relating to everyday life, is Dunbar’s “airport test.” A friend, he says, “is someone whom you will not hesitate to approach and greet if you chance to encounter them at 3 A.M. in the Hong Kong airport. You will know immediately where you know them from, to which social circle they belong, as well as their name and occupation. These are people whom you will not feel embarrassed to approach and speak to, because you’re familiar enough with them to know the nature of the relations between you.”

The broad definition of friendship, he claims, typically encompasses 150 people, who can be divided into different, concentric circles. The innermost circle contains no more than five intimate friends “who would donate a kidney to you if needed.” The second includes 12 to 15 good friends “who will help you in a difficult time and also mourn you when you die.” The 50 members of the third circle are people you would invite to your birthday party “but not necessarily for a [more intimate] meal in your home.” In the outer circle, bringing the total number to 150, are those “whose table you would feel sufficiently comfortable to join if you meet them at the bar.”

Social media, Dunbar relates, have helped him compile data on a vast scale and to corroborate his findings. He notes that “people often maintain that the number of 150 friends is illogical, because they have 500 friends on Facebook.” However, a “precise analysis” reveals that they do not really have 500 friends, but that the number of friends 61 million different users have “on average stood at exactly 149 friends,” he declares with unbridled satisfaction.

It’s not by chance that Dunbar’s number has remained more or less stable. After all, from his viewpoint it’s not a question of changing social circumstances, but of the evolutionary development of the human brain, and particularly the outer layer of the cerebrum, known as the neocortex, which, he notes, is responsible for emotional-social development in human beings: It constitutes the emotional reservoir from which a person draws the energy necessary to invest in and preserve social ties. People have a limited capacity for friendship, the professor adds: One person can have 30 good friends and another may have three, but at the end of the day, they will invest the same amount of time and energy in them.

Bonobo apes. Prof. Dunbar found “a direct correlation between the size of different regions in primates’ brains and the size of the group to which they belonged.”Credit: Georges Gobet/AFP

Dunbar’s initial field of research, in the 1980s, focused on the social development of primates. In it he discovered “a direct correlation between the size of different regions in primates’ brains and the size of the group to which they belonged.” For monkeys, this ranges from small groups of two or three individuals to very large groups of up to 55 members among chimpanzees and baboons, which possess the largest brain among all monkeys.

Extrapolating from what he saw as the direct link between primates’ brain size and the size of their groups, Dunbar concluded that if an average baboon is capable of maintaining social relations with 50 other baboons simultaneously – in humans, whose brain is three times larger and more developed, the number would be about 150. To verify the theory, he studied the way of life of different groups in centuries past and in the present, from tribes of hunters-gatherers in East Asia, to the number of members of a church in Britain, to the average number of guests at American weddings. “I think that altogether we have something like 24 different datasets, and the overall average of members in them is 155 exactly.”

So our sociability is determined from birth?

“Yes, but up to a certain point. The number of relationships that a person or an animal is capable of maintaining is a direct result of the brain size of each species. However, within that there is space for maneuver resulting from genetic differences, and from the quality of the connections between the different parts of the brain and the functioning of the neurons that connect them. You can say that all people have the same computer, but the question is what software you install to run that computer.”

Men don’t talk

Borrowing Dunbar’s metaphor, we can say that what his new book clearly shows is that when it comes to the perception of friendship, men and women have a different computer. In fact, the findings the professor presents sound so stereotypical that they almost make one uneasy. The simple conclusion deriving from them: Men are less sociable than women, not only in terms of the number of social ties they create, but also in terms of the nature of those ties. For women, he explains, “the most important element to preserve friendship is to converse with one another, whether in person or on the phone.” However, for men, “conversations had no impact on the prospect of preserving the social relationship.”

What’s important for men?

“Doing things together – going to a bar, watching a game, climbing – guys’ friendships are much more casual.”

Dunbar attributes these differences to the brain structures of women and men. “The wiring – the connection between the different parts of the brain – works better and more strongly in women,” he explains, meaning that the different parts of the female brain seem to communicate with each other far more efficiently. Among other things, this enables women to manage relationships on the basis of two different cognitive dimensions, whereas men have relationships that are more one-dimensional. “You can see it in the way that women’s friendship is far more intimate, so we see that if a woman’s friend moves away – [the woman is] on the Internet, Facebook, or phoning to keep the relationship going; for men, by contrast, a relationship is activity-dependent, so if one of them moves, the relationship will often be severed.”

That’s not the only gender-related difference: “For women, friendship is far more intensive and personal, with the emphasis on the other person. For men the whole concept of friendship is more facile, and bears the character of a social club. What’s important for a woman is the personality opposite her, whereas what’s important for men is whether you ‘belong to my club’ or not. As a result, conversations between women are far deeper, while between men conversations bear more of a competitive nature.”

Generally speaking, Dunbar explains that the largest number of friends and social connections exists when we’re in our 20s and early 30s. Moreover, among both humans and primates, the number of social ties is reduced when there are offspring to care for. On the other hand, once the offspring grow up, an opportunity is created to forge new relationships: “The social circle is fluid; we lose friends and acquire new friends all the time. In the 18- to 19-year-old age group, that occurs very frequently. It also happens in mid-life, but on a smaller scale and at a far slower pace.”

Is it true, as you write in your new book, that a romantic relationship exacts the price of losing two close friends?

“Yes, that is exactly what the studies show. An average person who is not in a romantic relationship has five friends on whose shoulders he can cry, those in the innermost circle. Generally speaking, it’s two friends, two relatives and another person, a friend or someone from the family. When a person is in an intensive relationship, the number drops to four, and includes the new romantic partner.”

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