The three types of friend you should drop, according to an expert

Robin Dunbar is a professor of anthropology at the University of Oxford, a renowned evolutionary psychologist and author of Friends: Understanding the Power of Our Most Important Relationships. According to his research, there are a myriad of psychological and physical health benefits from having just five intimate friendships and 150 people in our extended social networks. How do we choose who should go where? Follow the rule of seven. (Photo: Andre Camara)

The ideal number

Close friendships have a massive impact on your psychological wellbeing as well as your physical health. A torrent of research shows that friendship helps us live longer and protects us against disease, as well as physiological decline. Multiple studies across cultures have shown that five meaningful relationships across friends and family is the ideal number. I came to this work through decades of studying monkeys. I was interested in the factors that drive social evolution and group living in mammals. When I discovered the social brain hypothesis – the relationship between group size and brain size and primates, I was curious what it predicted for humans. (Photo: Thomas Barwick)

Babies can cause 'friendship cull'

The answer was 150. I rushed to the library trying to find out what the typical sizes of ethnographic groups are. We did a number of studies, we looked at Christmas card lists and social media contacts - indeed, it turns out to be 150. The average number of friends on 61 million Facebook pages was 150 – what is now known as Dunbar’s number. Over the lifespan, the number of friends forms a distinctive hump shape. At about 18, you would only list about 50 people; by the time you get to 20, you're running up to 250, partly because of exposure. Then it hits a high point in the early 20s. People at that stage are operating like careful shoppers, trying to meet as many people as possible to get the best choice for their lifelong friends. By about 30, it drops down to 150. There’s a big culling that goes on at that point, a lot of which – I say this mischievously – has to do with babies, because having them can be quite anti-social. (Photo: FatCamera)

Friendship groups 'heavily gendered'

Homophily – the idea that “birds of a feather flock together” – plays a big role in friendships. My research found that the more things you have in common with someone, the stronger the relationship and the longer it will last. Some of this is endogenous – it’s part of your biology or psychology. For example, we found that friendship networks are heavily gendered. Of women’s social networks, 75 per cent of them consist of women. (Photo: FlashPop)

Seven key pillars for social network

We ran a survey looking at people's social networks and discovered seven key pillars. They are: a shared language, being from the same location, similar education and career experiences, shared hobbies and interests, aligning world views, a similar sense of humour, and a shared music taste. The more you share with somebody, the stronger the friendship is. They may change with time and experience as you’re exposed to new opportunities. You discover new kinds of music, perhaps through other friends, or new comedians whose humour you like, or maybe you convert to another religion or political view. None of these are fatal for existing friendships. But they impose small amounts of stress and friction on the relationship because of differences of view. Over time you might drift apart. (Photo: Maki Nakamura)

Who to lose for good

If you're going to cull anybody this year, those are the ones you want to lose for good – the friendships where you eventually discover you share relatively few things in common. Those are the things that will make that friendship last. And in general, those are the friendships that are probably not going to last the test of time. I suggest starting with these three types of friends...(Photo: Nenad Stojnev)

The friends where conversation is an effort

The best friendships feel effortless. They’re the ones where you can have a meaningful conversation, where you don’t get bored. You’re not sitting there with your good friends thinking: "I've run out of things to say." You do that with strangers when you're trying to build a relationship, but you don't do that with well-established friends. (Photo: Jamie Grill)

The ones you don't trust

It also comes down to reciprocity. Do they ring you as often as you ring them? Do they include you in social activities? Invite you to their party? We subconsciously count up those kinds of signals. In some ways, you have to switch the brain off and let the body take over. There’s things we do when we meet somebody we know, and like in the street, a very set sequence of facial and head gestures. If you try to do it, you’ll invariably screw it up. It’s all about your natural instincts and the way you behave around people. In the end, relationships work on the basis of trust. Past experiences add up to give you a metric of trust – or lack of trust – and that’s the basis to decide whether a friendship is sustainable. (Photo: GCShutter)

The friendships of endless compromises

Introverts tend to have fewer friends, but because they devote more time to them, those friendships are stronger. Extroverts may have more friends but tend to be spread thinly with weaker friendships, which isn’t to say they might not have a very close friend. I tend to see this in terms of introverts being kind of risk averse. They really want to be sure that when their world falls apart and they ask for help, that friend will put down everything. Extroverts trade off their social confidence, if someone isn’t available, they’ll ask the next friend. Problems can arise when you have an extrovert and an introvert because they can't agree on what to do on a Saturday night, and now you've got a fracture line that builds up. We compromise all the time, but these stresses can build up and cause the relationship to fracture. (Photo: Catherine Falls Commercial)

How can you make new friends?

People often ask me how to make new friends. Find an activity that you enjoy, therefore you want to keep going back, where people gather. It doesn’t really matter what, as long as you enjoy it. It could be a choir or the golf club, as long as you can stare into the whites of somebody’s eyes. Physical proximity is often overlooked, but it goes on below the radar of consciousness in managing our friendships and relationships in general. (Photo: Morsa Images)

Don't overdo it

If you try to spread your time and emotional capital too thinly among too many people, you're likely to end up with rather weak relationships. My advice is to beware of overdoing it. We really do seem to have this need to have a few close friendships on which we depend. This is the five. Usually it consists of a couple of close family members and a few friends in the most meaningful sense of the word. The ones that remain, those five reciprocal relationships with whom you share the most pillars, those are the friendships that will sustain you for life. (Photo: Maskot)