Trends in Cognitive Sciences
Feature ReviewThe Anatomy of Friendship
Section snippets
The Meaning of Friendship
Over the past two decades, considerable evidence has emerged to suggest that the most important factor influencing our happiness, mental well-being, physical health, and even mortality risk, not to mention the morbidity and mortality of our children, is the size and quality of our friendship circles – something that also turns out to be true for anthropoid primates (Box 1). Friends provide moral and emotional support, as well as protection from external threats and the stresses of living in
The Limits to Friendship
Defining friendships in this wide sense, how many friends do we typically have? The average size of personal social networks seems to be about 150, whether these are determined from face-to-face contacts 18, 19, telephone call databases [20], or postings in online environments 21, 22, 23. This includes all extended family relationships as well as friends in the more conventional sense. More surprisingly, this turns out to be a common size for human organisations, including community size in
The Circles of Friendship
In contemporary societies, most personal social networks consist of extended family (including in-laws, or affines) and friends in about equal proportions [19]. These form two separate, but interlocked, subnetworks (family vs. friends) that typically interact only to a limited extent. Notably, we seem to treat close in-laws as though they were genetic family, and for the good biological reason that they share with us a genetic interest in our offspring [1]. People who come from large extended
A Two-Process Model of Social Bonding
In anthropoid primates, close friendships act as coalitions, one of whose functions is to buffer the individual, and particularly females, against the stresses that arise from living in close spatial proximity. Primates (and humans) live in groups mainly to minimise external ecological threats such as predation risk, raiding by neighbours, or environmental risk 50, 54, 55. In effect, primate groups are implicit social contracts: the relationships on which they are built are promissory notes
How Time Limits Friendship Networks
Time is a limited resource for all animals [77] including humans 78, 79, and if the quality (and hence functionality) of a relationship depends on the time invested in it [10], each individual has to decide how to distribute his/her available social effort, or capital, across his/her network. The network layers of Figure 2 appear to be associated with very specific contact values (Figure 3) 10, 19, 20. If someone is contacted less often than the defining rate (once a week for the 5-layer, once
A Crucial Role for Cognition
On the cognitive side, some form of cost accounting (a totting up of favours owed and promises broken) must be important [10]. A survey of the causes of relationship breakdown, for example, has identified lack of caring, poor communication, jealousy, and alcohol/drugs as the main causes (accounting for approximately 57% of all breakdowns) [122], all of which suggest that some kind of tally is being kept. However, there have been no studies that have explored the cognitive bases of this
The Seven Pillars of Friendship
One of the most striking things to emerge out of the friendship literature in the past decade or so has been the homophily effect: friends tend to be similar to each other on many dimensions (though personality is not often one of these) [155]. Personal social networks are commonly homophilous for gender, for example: men’s networks have significantly more men in them and women’s networks have significantly more women 26, 40. In part, this seems to reflect the fact that men and women have
Has the Internet Changed Our Social World?
A natural question to ask is whether the advent of the digital world, and social networking sites in particular, has changed any of these patterns. Relationships require a significant time investment (Figure 3) and there is a very strict upper limit of four on the number of people we can engage in conversation at any one time 133, 134, 135, 136, 137, 138, making it difficult, given the limit on the time available each day for social activities (approximately 20% of our day, based on activity
Concluding Remarks
Friendships (including family) are the single most important factor affecting our health and well-being. However, friendships are costly to maintain, both cognitively and in terms of the time that needs to be invested in them. These limit the number of friends we can have to around 150, and obliges us to distribute our social time/capital unevenly among them as a function of the benefits they provide us with. The endorphin system seems to play a crucial role in the maintenance of friendships,
Acknowledgements
Much of the research on which this article is based was funded by the British Academy Centenary Research Project, the UK EPSRC TESS project, the EU FP7 SOCIALNETS project and a European Research Council Advanced Investigator grant (No. 295663). I am grateful for the very helpful suggestions of the three referees.
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