By Robin Dunbar
Our social networks can have dramatic effects on our lives. Your chances of becoming obese, giving up smoking, being happy or depressed, or getting divorced are all influenced by how many of your close friends do these things. A good social network could even help you live longer since laughing with friends triggers the release of endorphins, which seem to “tune” the immune system, making you more resilient to disease. So what factors influence the form and function that our social networks take?
From as far back as hunter-gatherer societies, everyone in the community is related to everyone else, either as biological relatives or in-laws. In post-industrial societies this is no longer true – we live among strangers, some of whom become friends. As a result, our social circles really consist of two separate networks – family and friends – with roughly half drawn from each group.
Because the pull of kinship is so strong, we give priority to family, choosing to include them in our networks above unrelated individuals. Indeed, people who come from large extended families actually have fewer friends. One reason we favour kin is that they are much more likely to come to our aid when we need help than unrelated individuals, even if these are very good friends.
Family and friend relationships differ in other important ways, too. One is that friendships are very prone to decay if untended. Failure to see a friend for six months or so leaves us feeling less emotionally attached to them, causing them to drop down through the layers of our network hierarchy.
Family relationships, by contrast, are incredibly resilient to neglect. As a result, the family half of our network remains constant throughout most of our lives whereas the friendship component undergoes considerable change over time, with up to 20 per cent turnover every few years.
Although the average social network contains around 150 friends, there is considerable individual variation in the number of relationships; some people have fewer than 100, a few may have 250 or more. There are three main reasons for this: gender, social skills and personality.
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