How Many Friends Does One Person Need? (4 page)

But what about more technologically developed societies? Is there anything to suggest that the figure of 150 might be a relevant social unit? The answer is yes. Once you start to look for them, groups of about this size turn up everywhere. My colleague Russell Hill and I asked a number of people to make a list of all those to whom they sent Christmas cards. On average, sixty-eight cards were sent to households that contained a total of around 150 members.

The same figure turns up in business. A rule of thumb commonly used in business organisation theory is that organisations of fewer than 150 people work fine on a person-to-person basis, but once they grow larger than this they need a formal hierarchy if they are to work efficiently. Sociologists have known since the 1950s that there is a critical threshold in the region of 150 to two hundred, with larger companies suffering a disproportionate amount of absenteeism and sickness. Famously, Mr Gore, the founder of GoreTex, one of the most successful of all medium-sized companies, insisted on creating completely separate factory units each with about 150 workers rather than just making his main factory larger when the growth of his business demanded more production – something that I suspect was the key to the success of his enterprise.

By keeping his factory units below the critical size of 150, he was able to do away with hierarchies and management structures: the factory worked by personal relationships, with a sense of mutual obligation encouraging workers and managers to co-operate rather than compete.
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Military planners seem to have come up with the same rule of thumb too. In most modern armies, for example, the smallest independent unit is the company, which normally consists of three fighting platoons of thirty to forty soldiers each plus the command staff and some support units, making a total of 130–150. Even the basic fighting unit of the Roman army during the Republic (the man-iple, or double century) was of similar size, containing roughly 130 men.

Even academic communities may be limited in the same way. In a survey of twelve disciplines from both the sciences and the humanities, Tony Becher of the Education Department in the University of Sussex found that the number of researchers whose work an individual was likely to pay attention to was between one hundred and two hundred. Once a discipline becomes larger than this, it seems that it fragments into two or more sub-disciplines.

In traditional societies, village sizes seem to approximate this, too. Neolithic villages from the Middle East around 6000 bc typically seem to have contained 120 to 150 people, judging by the number of dwellings. And the estimated size of English villages recorded by William the Conqueror’s henchmen in the
Domesday Book
in 1086 also seems to have been about 150. Similarly, during the eighteenth century the average number of people in a village in every English county except Kent was around 160. (In Kent, it was a hundred... I wonder what that tells us about the folk there?)

The Hutterites and the Amish, two groups of contemporary North American religious fundamentalists who live and farm communally (the one in the Dakotas, the other in Pennsylvania), have average community sizes
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of around 110, mainly because they split their communities once they exceed 150. What is interesting is the reason the Hutterites themselves give for splitting communities at this number. They find that when there are more than about 150 individuals, they cannot control the behaviour of the members by peer pressure alone.

What keeps the community together is a sense of mutual obligation and reciprocity, and that seems to break down once community size exceeds about 150. Since their whole ethos is against having hierarchies and police forces, they prefer to split the community before they get to that point.

One way of defining Dunbar’s Number is as the set of people who, if you saw them in the transit lounge during a 3 a.m. stopover at Hong Kong airport, you wouldn’t feel embarrassed about going up to them and saying: ‘Hi!

How are you? Haven’t seen you in ages!’ In fact, they would probably be a bit miffed if you didn’t. You wouldn’t need to introduce yourself because they would know where you stood in their social world, and you would know where they stood in yours. And, if push really came to shove, they would be more likely than not to agree to lend you a fiver if you asked.

Is this apparent cognitive limit on the size of human groups a reflection of a memory overload problem (we can only remember 150 individuals, or only keep track of all the relationships involved in a community of 150) or is the problem a more subtle one – perhaps something to do with an information constraint on the quality of the rela-
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tionships involved? Let me give just two bits of evidence that point to the second as the more likely.

One of these derives from the fact that it is extremely common in primates for there to be a relationship between a male’s dominance rank and the number of females with whom he is able to mate. One prediction we can make off the back of the social brain model is that the correlation should be much poorer in those species which have a relatively larger neocortex because they can use their big computers to find ways round simple dominance-based strategies. Hence, we should find a negative correlation between neocortex volume, on the one hand, and the correlation between male rank and mating success, on the other. And this is exactly what we see in the data for monkeys and apes. Lower-ranking males in species with relatively large neocortices are able to undermine the dominance of high-ranking males and get the females to mate with them. They do this by exploiting more subtle social strategies – forming coalitions with other males to undermine the power-based ranks of dominant males, exploiting female preferences, and so on.

The second example comes from an analysis carried out by Dick Byrne of St Andrews University. He and his colleague, Andy Whiten, had put together an extensive catalogue of examples of tactical deception from the literature on primates. Tactical deception is the term used to refer to cases in which one animal exploits another to gain an objective. Species that have bigger neocortices do more tactical deception.

One of the classic examples of tactical deception is the case of the female hamadryas baboon deceiving her male.

Hamadryas baboons live in harem-like family units (a
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male with one to five females), with ten or fifteen of these family units making up a band that lives and stays together.

The males are fiercely protective of their females, and will not tolerate them getting near to other males. They do this by punishing the females if they stray too far from them, and particularly if the female allows another male to get between her and the harem male. The Swiss zoologist Hans Kummer once watched a female spend twenty minutes inching her way from where the rest of her family unit was feeding to get behind a big rock. Behind the rock there was a young male from a neighbouring unit, and once there she started to groom with him. It seemed to Kummer that, while the female was behind the rock grooming this young male, she made a very concerted effort to make sure that her head was always visible to her male above the rock as he continued feeding some metres away.

There are two possible interpretations of her behaviour. From a strictly behaviourist point of view, you might argue that she was worried about the consequences of her action, having learned that not keeping within her male’s view invited trouble. A more generous cognitive interpretation is that she was thinking something like the following: ‘As long as the old gaffer can see my head he will think I am just sitting here innocently behind a rock and so I can get away with whatever it is I am trying to do.’ The suggestion of the latter interpretation is that she was manipulating the mental state of her male.

I suspect that what she was actually doing was not quite so sophisticated as the second interpretation (though such claims have become quite common among scientists who study animal behaviour and cognition in
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recent years). However, irrespective of which explanation is right, behaviour of this subtlety is far from unusual among monkeys and apes – and almost unheard of among any other non-primate species. In the study of animal (and human developmental) cognition, the phenomenon is now referred to as ‘mentalising’ – being able to understand the minds of other individuals rather than simply working in terms of simple descriptions of their behaviour. The belief is that whereas all other animals function like behaviourists have always supposed (they learn rules of behaviour), monkeys and apes have shifted gear just enough to be able to work in terms of understanding at least a little bit of the mind behind the behaviour.

Evidence of this kind pushes us towards the view that it is something about the
quality
of the relationships that is important, not just their absolute number. We find an upper limit on group size because this is the limit of the number of relationships that an animal can maintain at this level of complexity. It’s not just a matter of remembering who is who, or how
x
relates to
y
and both relate to me, but rather how I can use my knowledge of the individuals involved to manage those relationships when I need to call on them.

Primates are above all social animals: that is their big evolutionary breakthrough. It’s what has made them as successful as they have been and, by extension of course, it is what makes humans so successful – we have inherited the same social expertise. What marks primates (or at least monkeys and apes) out as different from all other species of animals is the sheer intensity of their social interactions. The difference between the rest of our pri-
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mate cousins and us is simply that we have taken this trend to a whole new level.

Noah, it is said, counted the animals into his Ark two by two. Perhaps sensibly in view of the circumstances, he was no doubt thinking in terms of reproduction. Had he been thinking socially, he might instead have counted his animals by threes. That, at least, is the message of several recent studies suggesting that our social networks have a very distinctive structure based on multiples of three.

We all know that we can distinguish friends from acquaintances by how we feel about them. Friends are those we want to spend time with, whereas acquaintances are those whose company is more of a momentary convenience. But it seems that we make even finer judgements than this in real life. What’s perhaps more intriguing is that if you look at the pattern of relationships within the group of 150 that constitutes our social world, a number of circles of intimacy can be detected. The innermost group consists of about three to five people. These seem to constitute the small nucleus of really good friends to whom you go in times of trouble – for advice, comfort, or perhaps even the loan of money or help. Above this is a slightly larger grouping that typically consists of about ten additional people. And above this is a slightly bigger circle of around thirty more.

The numbers that make up these circles of acquaintanceship seem to have no obvious pattern. But if you consider each successive circle inclusive of all the inner circles, a very clear pattern emerges: they seem to form a sequence that
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goes up by a factor of three (roughly five, fifteen, fifty and 150). In fact, there are at least two more layers beyond this: there is a grouping at about five hundred and another at about fifteen hundred. And the Greek philosopher Plato even managed to get the next layer out: he identified 5,300 (and I’ll happily allow him the extra three hundred) as the ideal size for a democracy...

We are not sure what all of these successive circles correspond to in real life, or why they should increase in size by a multiple of three, but some correspond to very well-known groupings. The grouping of twelve to fifteen, for example, has long been known to social psychologists as the ‘sympathy group’ – all those whose death tomorrow would leave you distraught. Curiously, this is also the typical team size in most team sports, the number of members on a jury, the number of Apostles... and the list goes on. The fifty grouping corresponds to the typical overnight camp size among traditional hunter-gatherers like the Australian Aboriginals or the San Bushmen of southern Africa. And 1,500 is the average size of tribes among hunter-gatherer peoples (usually defined as all the people that speak the same language, or, in the case of very widespread languages, the same dialect).

It seems that each of these circles of acquaintanceship maps quite neatly onto two aspects of how we relate to our friends. One is the frequency with which we contact them – at least once a week for the inner circle of five, at least once a month for the circle of fifteen, at least once a year for the 150. But it also seems to coincide with the sense of intimacy we feel: we have the most intense relationships with the inner five, but we have a slightly cooler relationship with the ten additional people that make up
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the next circle of fifteen. And successively cooler still are our feelings towards the next two layers (those in the circles of fifty and 150).

So it seems as though there is a limit to the number of people we can hold at a particular level of intimacy. There are just so many boxes you can fill in your innermost circle, and if a new person comes into your life, someone has to drop down into the next level to make room for them. Interestingly, kin seem to occur more often than you would expect by chance in each of these successive levels. This isn’t to say that we have to include (or even like!) all our kin, but it does seem that kin get given preference: when all else is equal, blood really is thicker than water and we are more willing to help them out.
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Community is what makes the world go round. In that respect, we are very much in tune with our primate heritage: sociality, often a very intense form of sociality, is the hallmark of the monkeys and apes. It was the big key to their – and our – evolutionary success. And the core of that sense of community – especially in humans – is kinship. Kinship provides a surprisingly deep and sometimes unrecognised framework for our social life, not just in traditional small-scale societies, but for us today as well.