I just love this article – it sheds some light on the most essential thing that we as human beings and social animals have in common – how to create and maintain relationships with people who we are willing to connect with. There are things which you will learn that will take you by surprise, I promise!
This article was published in New Scientist on 3 March 2021
By Robin Dunbar
Evolutionary psychologist Robin Dunbar has found that our friendships are governed by secret rules, based on everything from your sex to your sleep schedule. Our unique social fingerprints help determine who we are drawn to, which friendships last and why some friends are ultimately replaceable.
FACEBOOK users used to have a lot more friends. The social networking site pursues a commercial strategy of trying to persuade people to “friend” as many others as possible. However, sometime around 2007, users began to question who all these people they had befriended were. Then, someone pointed out that we can only manage around 150 relationships at any time. A flurry of “friend” culling followed and, since then, the number 150 has been known as “Dunbar’s number”. Thank you Facebook!
Modern technology may have brought me notoriety, but Dunbar’s number is rooted in evolutionary biology. Although humans are a highly social species, juggling relationships isn’t easy and, like other primates, the size of our social network is constrained by brain size. Two decades ago, my research revealed that this means we cannot meaningfully engage with more than about 150 others. No matter how gregarious you are, that is your limit. In this, we are all alike. However, more recent research on friendship has uncovered some fascinating individual differences.
My colleagues and I have made eye-opening discoveries about how much time people spend cultivating various members of their social networks, how friendships form and dissolve and what we are looking for in our friends. What has really surprised us is that each person has a unique “social fingerprint” – an idiosyncratic way in which they allocate their social effort. This pattern is quite impervious to who is in your friendship circle at any given time. It does, however, reveal quite a lot about your own identity – and could even be influencing how well you are coping with social restrictions during the covid-19 pandemic.
Layers of intimacy
The typical social circle of 150 people is made up of a series of layers, each containing a well-defined number of people and associated with specific frequencies of contact, levels of emotional closeness and willingness to provide help (see “The structure of friendship”). In fact, our social world consists of two quite distinct sets of people: friends and family. What’s more, we tend to give preference to the latter. With our social networks limited to around 150 relationships, we first slot in family members and then set about filling any spare places with unrelated friends. As a result, people who come from large families tend to have fewer friends.
Some years ago, I examined evidence from various cultures and economies to try to find out how much time we actually spend on social interactions with our friends and family. I found around half a dozen studies where researchers had recorded the amount of time in the day that people devoted to different activities, including things like sleeping, cooking, relaxing and interacting socially. This gave me a diverse selection of societies: Maasai pastoralists in East Africa, Nepalese hill farmers, New Guinea horticulturalists, agricultural tribes in sub-Saharan Africa, !Kung San hunter–gatherers from southern Africa and housewives in Dundee, UK. My analysis revealed that people spent around 20 per cent of their time, on average, on social interactions. That’s about 3.5 hours a day talking, eating and sitting with people in a social context.
“We all spend about 20 per cent of our time, on average, on social interactions”
This may seem like a lot, but distributed evenly among your 150 friends and family, it works out at just 1 minute and 45 seconds per person per day. Of course, that isn’t what we do. Around 40 per cent of this social time is devoted to the five people in our innermost social circle, the support clique, with another 20 per cent given to the 10 additional people in the next layer, the sympathy group. That’s about 17.5 minutes and 4.5 minutes per person, respectively. The remaining 135 people in the two outer rings of our social circles get an average of just 37 seconds a day each.
These interactions are often not face to face, of course. Throughout most of human evolution, people lived in the same village as their friends and family, but today our social circles are far more geographically dispersed. In social networks, there is a very strong effect called the 30-minute rule that dictates how long you are willing to travel to go to see someone. It doesn’t matter much whether this is on foot, by bicycle or by car: it’s the psychological significance of the time it takes you that counts. Surprisingly, though, research reveals that we are also more likely to phone or text friends if they live nearby. For example, one study found that the frequency of phone contact between friends declined gradually the further apart they lived, with a sharp drop-off at about 160 kilometres.
Subconsciously, we seem to be aware that failure to contact someone will weaken a relationship, so we make up for it. Analysing mobile phone records, Kunal Bhattacharya and Asim Ghosh at Aalto University, Finland, found a correlation between the length of the gap since the last call and the duration of the next call – for special friends, but not for weaker friendships. Indeed, humans aren’t alone in making such subconscious calculations. I saw something similar in gelada baboons I was studying in Ethiopia. As their infants grew, mothers were forced to spend more time feeding, leaving less time to groom their main social partners – their best friends forever (BFFs). Instead, they relied on the friends to do all the work to keep the relationship going. However, once the infant had started to wean, they paid back the debt, devoting much more time to grooming the BFFs than the BFFs groomed them.
Oiling your contacts
Such behaviours matter because friendships are fragile. Unlike family bonds, they depend on you investing enough time and effort in each other to keep the relationship well oiled and functional (see “Six rules for keeping your pals”). If you see someone less often, whether deliberately or by force of circumstance, that relationship will weaken. Bob Kraut at Carnegie Mellon University in Pennsylvania calculated that a friendship of high strength will decline to no more than a mere acquaintanceship in just three years. To be fair, there are a few friendships that stand the test of time and absence: usually no more than three or four, and they tend to be people we were particularly close to in early adult life. However, until the internet, social media and mobile phones became widely available a mere decade ago, friendships would have died naturally if someone moved away.
Is that changing? To take a closer look, Sam Roberts at the University of Chester, UK, and I studied a group of 30 students – half of them female, half male – to find out how moving away from home affected their social networks. We picked them up in their final term at school and monitored them through the following 18 months to the end of their first year at university. The deal was that we gave them a free mobile phone subscription in return for being able to download their monthly bills so we could see who they phoned and texted. They also had to fill in a questionnaire at the beginning, middle and end of the study telling us who everyone in their network was, how emotionally close they felt to each person, when they had last contacted them and how, and what they had done with them when they met face to face.
“Our study had revealed that people have a unique social fingerprint”
We collected huge quantities of information. (We were particularly impressed by three of the students who sent an average of 100 texts a day – and kept this up for the entire duration of the study.) Luckily, I was collaborating at the time with some physicists on a project about online networks and persuaded a couple of them to help with the complicated task of analysing the data. We were amazed by what we found.’
We could see the layers of the students’ social circles very nicely. What we hadn’t expected, however, was the fine detail in how individuals allocated their social effort. Each showed a distinct pattern in the frequency with which they called friends. One might call their best friend 30 times a month and their second best friend 10 times, while another would call their two top friends 20 times each, for example. But that wasn’t the most surprising thing. There was an average of around 40 per cent turnover in network membership over the 18 months – which is fairly normal for young adults – yet, when we looked at the patterns of contact before and after a change in friendship, they were almost identical. It seems that when we replace someone in our social network, we slot the new friend into exactly the same position the old one previously occupied in terms of the frequency with which we contact them. Our study had revealed that people have a characteristic social fingerprint.
How often you contact each of your friends probably reflects aspects of your personality, such as extraversion, neuroticism and conscientiousness. Our analysis revealed another factor influencing your social fingerprint: whether you are male or female. Over the course of the study, some friendships held up better than others, and we wondered why. The answer tended to differ between the sexes. For the girls as a whole, the activity most effective in preserving a pre-university friendship was talking together, whether in person or by phone. For the boys, talking had absolutely no effect on how likely a friendship was to survive. What made the difference was doing stuff together more often than they had before – going to the pub, playing sports, climbing mountains or whatever. Such activities also had a positive effect on the girls’ friendships, but it was nowhere near as great.
Calling patterns
This could have implications for how well our friendships are bearing up during the pandemic, while face-to-face meetings are restricted. It might also help explain a difference we found in the amount of time girls and boys spent on the phone. Of course, there were big individual variations, but for girls, calls averaged 150 seconds in the morning, rising to 500 seconds by the end of the day. Boys’ calls, by contrast, averaged just 100 seconds throughout the day.
Further analysis, led by Talayeh Aledavood at Aalto University, revealed another aspect of our identity with an influence on our social fingerprint. When we looked at the times at which our students were calling and texting, they found clear differences. Some were most active on their phones during the day and others used them mostly at night. We also found that those who were early birds, or larks, at the start of the study were still larks 18 months later, and the night owls at the start were still owls at the end – despite the turnover in their friends. That may not be so surprising, but being a lark or an owl turns out to have big implications for your social network.
Aledavood discovered this when she and her colleagues analysed a similar data set of 1000 Danish university students. Being a much larger group, it allowed them to look at the relative frequencies of communication of larks and owls in more detail. Some 20 per cent of the students were committed larks, the same proportion were committed owls and the rest were neither one nor the other. Larks showed no particular preference for having larks as friends, but owls favoured associating with owls, strongly reinforcing research showing that what we most want in a friend is someone just like us (see “Seven pillars of friendship”). Owls also had larger social networks than larks, at least in terms of the number of people they phoned frequently – 35 rather than 28. However, they spent less time on the phone to each friend – 94 seconds compared with 112 seconds, on average, for larks – so their networks weren’t as well integrated and reinforced. Again, restrictions to our social lives caused by covid-19 may be proving more disruptive to some friendships than others.
I hadn’t anticipated quite how much we would learn from scrutinising the mobile phone bills of students. I was surprised to find that everyone appears to have their own unique social fingerprint, and intrigued to discover that aspects of an individual’s social style influence their friendship choices. What was most unexpected, however, is the durability of a person’s social fingerprint in the face of change. It is as though exactly who our friends are doesn’t really matter, as long as we have friends. Of course, we opt for people who are as congenial as possible, but, provided these boxes are ticked, more or less anyone will do. That may sound opportunistic or even callous, but it makes sense. Friendship isn’t just for fun; it has huge benefits for our mental and physical well-being. In a changing world, our approach to making and maintaining friends needs to be both flexible and stable so that we can optimise those benefits.
Six rules for keeping your pals
Friends come and go for all sorts of reasons, but if you want to keep a friendship alive, you must obey these six rules:
1. Stand up for friends in their absence
2. Share important news
3. Provide emotional support when it is needed
4. Trust and confide in one another
5. Volunteer to help when a friend needs you
6. Try to make your friends happy
Seven pillars of friendship
Our friends tend to be surprisingly like us, and there are certain personal characteristics that predict how close a friendship is likely to be:
1. You speak the same language or, better still, dialect
2. You grew up in the same area
3. You have the same educational and career experiences
4. You pursue the same hobbies and interests
5. You see eye to eye on moral, religious and political matters
6. You share a sense of humour
7. You have the same taste in music
This article was originaly published in New Scientist