According to the General Social Survey (GSS), the number of Americans who say they have no close friends has roughly tripled in recent decades. Asked how many close confidants they have, most people’s response is “zero”.  And adult men seem to be especially bad at keeping and cultivating friendships.

This may seem odd in the era of Facebook, Twitter, Instagram, and our numerous social media options. But the “friends” in your digital galaxy aren’t the ones that matter when it comes to your health and happiness.

Dr Robin Dunbar, an evolutionary psychologist at the University of Oxford, was one of the first to recognise that the size of a human’s social network is limited.

Dunbar became convinced that there was a ratio between brain sizes and group sizes through his studies of non-human primates.

This ratio was mapped out using neuro-imaging and observation of time spent on grooming, an important social behaviour of primates. Dunbar concluded that the size, relative to the body, of the neocortex – the part of the brain associated with cognition and language – is linked to the size of a cohesive social group. This ratio limits how much complexity a social system can handle.

He determined “Dunbar’s number” which he says is the number of relationships you can actually manage effectively. That number — usually cited as 150 (though actually it is a range between 100 and 200) is the approximate size of a person’s social circle or number of an ever-changing group of friends and family members one would invite to a large party.

150 is the approximate size of a person’s social circle or number of an ever-changing group of friends and family members one would invite to a large party.

Dunbar also says the closest 15 relationships — including family members or “kin” — seem to be most crucial when it comes to somebody’s mental and physical health.

According to Dunbar, this rule of 150 is as true for early hunter-gatherer societies as it is for a surprising array of modern groupings: offices, factories, residential units, military organisations, even Christmas card lists. Go over 150, and a network is unlikely to last long or cohere well. Could it be the reason why the first people to move into cities decided that, to avoid alienation or tensions, they would found quasi-villages within their cities, much like Pisa’s 17 contrade, once 59?

Certain organisations have taken this idea to heart. The Swedish Tax Authority, for instance, has restructured its offices to stay within the 150-person threshold.

Now, some people I know would dispute this number hotly. They would triumphantly point to their 1,000 or even 5,000 friends on

their Facebook pages, ranging from family members through work colleagues to acquaintances in far-off corners of the world they have never visited. But is this really true? How many real friends do people have on today’s social media, like Facebook, Twitter and Instagram?

Facebook itself did a survey of its accounts about a year ago and found that the average number of friends was between 120 and 130. The distribution is, of course, skewed, with a long tail to the right. Some people really do number their friends in the thousands, but they are in fact few and far between. And many of these cases are actually professional accounts held by writers, journalists, and musicians who use Facebook as a fan base.

Not everyone subscribes to the social brain hypothesis. Some are sceptical about the possibility of deriving a magic number for social interaction at all. Granted, the correlation has been confirmed in other studies. However, the correlation can disappear when adding more data to statistical models, such as information about other aspects of primate life. 

For example, some researchers have found that primate neocortex and brain sizes may be better predicted by diet than by sociality. I am inclined to agree, given that I always see the same set of people congregating near Maxim’s Pastizzeria in Naxxar every morning. I am sure some people will have made the same observation about the crows near Is-Serkin in Rabat.

“Although there are many factors that can limit the number of relationships that we create and maintain, these studies help us to better understand … and measure such variables’ influence,” says Cristina Acedo Carmona, an anthropologist and economist at the University of León in Spain.

Among those who agree that a Dunbar-ian number can be found, some contest whether it’s 150. Research on varied social groups in the US suggests that their social networks cluster around 290 in size. And these numbers may be significantly skewed by outliers.

Patrik Lindenfors, Andreas Wartel, and Johan Lindt have investigated the empirical underpinnings of Dunbar’s number, and found that it doesn’t stand up to scrutiny when larger datasets and more modern statistical methods are used.

While the human brain is anatomically remarkably similar to that of other primates, it functions differently in terms of memory and information processing.

One crucial difference between humans and other animals is that non-human species only have a limited capacity to recognise ordered sequences of information, for example a string of words. This key cognitive element, which sets humans apart from other animals, may explain why only humans learn languages and flexibly plan for the future.

With all this in mind, the three researchers replicated Dunbar’s original analysis with a larger dataset and more advanced statistical methods. To ensure robust results, they used three different but overlapping datasets, two different statistical approaches, and carried out analyses both including all primates, and a more limited sample including only monkeys and apes.

Their results were clear. Estimates of Dunbar’s number were highly inconsistent, and the 95% confidence intervals – a measure of the certainty of the estimates – were consistently far too large to specify any one estimate as a cognitive limit on human group size.

The question of friendship is an eternal one. Thousands of years ago, Aristotle described three types of friendships — utility, pleasure, and good.

Friendships of utility, he said, are the friendships we have with folks with whom we share carpool duty, or whose home we keep an eye on while they’re out of town because we’ll need them to pick up our mail when we go on vacation next month.

Friendships of pleasure are those that are all about simply enjoying one another’s company and having a good time together. This type of friendship includes somebody that you like having drinks with on summer evenings or the crowd you always get a coffee with after a football match.

Friendships of the good are those based on mutual respect, admiration, and appreciation for the qualities each of you brings to the relationship. These may begin as a function of shared interests, or shared life stage, but the spark between the two friends is lit and the opportunity for increasing mutual self-disclosure and connection is harvested.

The circle of friendship may also be influenced by generational differences. Dunbar’s own research found that those aged 18–24 have much larger online social networks than those aged 55 and above. It could well be that the primacy of physical contact in the social brain hypothesis may apply less to young people who have never known life without the internet, for whom digital relationships may be just as meaningful as analogue ones.

Personally, I am not one who has had hundreds of friends. I tend to prefer a small number of intimate friendships, guided by Muhammad Ali who once said that “Friendship is the hardest thing in the world to explain. It’s not something you learn in school. But if you haven’t learned the meaning of friendship, you really haven’t learned anything”, or by Tennessee Williams who remarked that “Life is partly what we make it, and partly what it is made by the friends we choose.”