There is a limit to the number of friends we can manage at any one time, Dunbar’s number, imposed by a combination of the time and the cognitive demands of maintaining relationships. ⦁ There are striking gender differences in how relationships are maintained

The Anatomy of Friendship. R.I.M. Dunbar. Trends in Cognitive Sciences, Volume 22, Issue 1, January 2018, Pages 32–51. https://doi.org/10.1016/j.tics.2017.10.004

Abstract: Friendship is the single most important factor influencing our health, well-being, and happiness. Creating and maintaining friendships is, however, extremely costly, in terms of both the time that has to be invested and the cognitive mechanisms that underpin them. Nonetheless, personal social networks exhibit many constancies, notably in their size and their hierarchical structuring. Understanding the processes that give rise to these patterns and their evolutionary origins requires a multidisciplinary approach that combines social and neuropsychology as well as evolutionary biology.

Trends
⦁    Having friends has dramatic effects on our happiness, mental well-being and longevity.
⦁    There is a limit to the number of friends we can manage at any one time, sometimes known as ‘Dunbar’s number’.
⦁    This limit is imposed by a combination of the time and the cognitive demands (the latter a function of prefrontal cortex volume) of maintaining relationships.
⦁    There are striking gender differences in how relationships are maintained.
⦁    The Internet has not (yet) changed any of this.

Keywords: endorphins; gender differences; happiness; health; social networks

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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 accounting process (other than to emphasise the obvious need to remember past interactions).

The data on relationship breakdown should remind us that trust plays a crucial role in building and maintaining relationships [10,123,124]. The functionality of friendships (emotional support, unstinting help) depends implicitly on trust that, over the long haul, the relationship will be in approximate economic balance (i.e., debts will be repaid eventually). While close friendships (those in the innermost layers) may well involve unstinting altruism and, at least in the short term, less emphasis on scorekeeping, score-keeping and the monitoring of reputations are none-theless likely to become increasingly important in the outer layers. Interestingly, despite the kinship premium, breakdown of family relationships is unexpectedly common compared to friendships [122]. This may be because, whereas friendships simply drift apart after minor breaches of trust, kin (and romantic partners) are initially more tolerant but eventually, after many breaches of trust, so much strain has been put on the relationship that it undergoes a catastrophic fracture. As a result, the sense of ‘hurt’ is greater and reconciliation is invariably difficult to engineer [122].

Friendships are cognitively demanding because they are implicit social contracts – in effect, promises of future support. This makes them particularly susceptible to freeriding (taking the benefits without paying all the costs). Freeriding, in its many forms (stealing others’ property, reneging on obligations, behaving ungenerously and, at least in humans, trading once too often on someone’s good nature or spreading rumours about their motives), is very destructive of relationships and rapidly leads to the collapse and contraction of social networks because people become unwilling to trust more than their closest friends [125,126].

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Gendered Networks?

Aside from striking gender homophily of networks [26,40], the two sexes exhibit a number of important differences in respect of friendships. One is that, while both sexes have broadly similar social networks, women consistently have larger inner layers than men, in most cases significantly so [18,127,129]. This correlates with women’s typically better performance on mentalising tasks [127,132]. Second, women seem to have a category of friend that is almost unknown among men, namely, a same-sex best friend (a BFF, or ‘best friend forever’), in addition to a romantic partner [216]. Although this additional individual is occasionally male, the great majority are women: in a sample of 257 women’s best friends, just 18.3% were men [217]. It is unlikely that many of these male BFFs were extra lovers, since it seems difficult to maintain two equally intense sexual relationships simultaneously [85].

The two genders also differ in what maintains the emotional closeness of friendships over time. For women, this involves making the effort to spend more time talking together (either face-to-face, by phone or via the Internet), whereas talking has almost no effect on men’s friendships; what maintains the emotional quality of men’s friendships is increased investment in ‘doing things together’ (sports, drinking, etc.) [91]. Although doing things together does benefit women’s friendships, it has much less effect than it does for men.

These contrasts parallel differences in social media and phone use (women account for around two-thirds of active Facebook users [218,219] and make longer and more frequent phone calls [29]) as well as differences in style of aggression (men are more likely to respond with physical violence, while women are more likely to use verbal aggression [220]). Analyses of a large national mobile phone database suggest that women focus their phone calling on an opposite sex person of similar age much more than males do, and they do so from a much earlier age and continue for considerably longer [221].

In sum, women seem to invest more heavily in their relationships than men, whose relationships seem to be much more casual (even in the case of their most intimate relationships) [217]. For this reason, women’s friendships often seem to be more fragile and susceptible to catastrophic breakdown [122].


Check also Optimising human community sizes. R.I.M. Dunbar, R. Sosis. Evolution and Human Behavior, http://www.bipartisanalliance.com/2017/11/group-longevity-as-function-of-its-size.html