Dunbar Number and Facebook
Not many people have a number named after them, but Robin Dunbar lays claim to the Dunbar Number. … a commonly cited approximation is 150 – and this is the number of people with whom we can maintain a meaningful relationship, whether in a hunter-gatherer society or on Facebook.
…[Dunbar is …]The director of the Institute of Cognitive and Evolutionary Anthropology at Oxford University. …
What does your work tell us about the way we interact socially?
The way in which our social world is constructed is part and parcel of our biological inheritance. Together with apes and monkeys, we’re members of the primate family – and within the primates there is a general relationship between the size of the brain and the size of the social group. We fit in a pattern. There are social circles beyond it and layers within – but there is a natural grouping of 150.
This is the number of people you can have a relationship with involving trust and obligation – there’s some personal history, not just names and faces, as is frequently the case with Facebook.
And this is is the Dunbar number! How did you come up with this concept?
I was working on the arcane question of why primates spend so much time grooming one another, and I tested another hypothesis – which says the reason why primates have big brains is because they live in complex social worlds. Because grooming is social, all these things ought to map together, so I started plotting brain size and group size and grooming time against one another. You get a nice set of relationships.
It was about 3 am, and I thought, hmm, what happens if you plug humans into this? And you get this number of 150. This looked implausibly small, given that we all live in cities now, but it turned out that this was the size of a typical community in hunter-gatherer societies. And the average village size in the Domesday Book is 150 [people].
It’s the same when we have much better data – in the 18th century, for example, thanks to parish registers. County by county, the average size of a village is again 150. Except in Kent, where it was 100. I’ve no idea why.
Has this number evolved at all?
The Dunbar number probably dates back to the appearance of anatomically modern humans 250,000 years ago. If you go back in time, by estimating brain size, you can see community size declining steadily.
How can we grow the Dunbar number?
We’re caught in a bind: community sizes were designed for hunter-gatherer- type societies where people weren’t living on top of one another. Your 150 were scattered over a wide are, but everybody shared the same 150. This made for a very densely interconnected community, and this means the community polices itself. You don’t need lawyers and policemen. If you step out of line, granny will wag her finger at you. …
The alternative solution, of course, is that we could evolve bigger brains. But they’d have to be much bigger, and it takes a long time.
And Now the Essay …
Until 2007 I lived in a pleasant, upper-middle-class neighborhood in the hills in Oakland. Just about everyone on our street knew each other. We got our families together every Friday in the summer for picnics, a tradition that had been going on for decades. We Christmas caroled together and had holiday parties together.
But the scene in Oakland has changed in frightening ways over the last two years, ways that have changed even that little neighborhood. This June I heard about an awful incident on the street. A young mother was awakened at 2 AM by her dog barking and went downstairs to find two men, armed with guns, in her house. They took her outside into the trees and raped her, then robbed the house. Her two small children were asleep in the house.
Horrific and traumatic and this incident was, it was not an isolated incident. On this street of fewer than 20 houses there have been six armed home burglaries in the past year and a half. Armed burglaries are spreading across the city and the East Bay and seem unstoppable. Police, surveillance cameras on telephone poles and on houses, dogs, burglar alarm systems and signs, neighborhood watch—nothing has had much effect, though a few people have been arrested.
With news like this becoming a common occurrence, you can imagine that people feel completely vulnerable. It is a breakdown of civilization. In truth, civilization has been breaking down for quite a while now in Oakland, under the weight of poverty and drugs. But though we may be late in asking, we should ask: what is happening and why? These are the questions I am going to discuss in this essay.
To begin, I am going to ask you to try to put away your ideas of who human beings are and how they act. We tell ourselves many myths about our rational motivations that don’t work well to explain the situation I just described. Instead, I’d like to delve into what our biology has evolved human nature to be and how that human nature limits and determines our behavior on the scale of communities.
So who are we? For over 6 million years—that is 6 million years—our ancestors, the hominids, lived in small groups that hunted and foraged for food. In a situation like that, where you might find an animal and kill it today, but more food might not turn up for five more days, survival of the whole group depends on sharing food. We share first with those most closely related to ourselves—our children, for example. If we don’t, our genes die out and that behavior dies out. So we all evolved to first share with close relatives.
But, as I’ve been reading, in such a small group in such harsh conditions, we also need to share with those in need to whom we are not related, or the group will not survive. In other words, out of self-interest we evolved to be altruists. And we are a special kind of altruist called “reciprocal altruists”. If I share with you today because you have a need, I expect that you will reciprocate later when I am the one in trouble.
But what exactly is it that evolved that makes us altruists? Evolution evolved in us feelings—feelings of sympathy, obligation, guilt, friendship, affection, and trust, and toward those who do not reciprocate properly, outrage and dislike. These feelings are what we use to decide what to do in a given situation—to help, or not to help, for instance. In other words, these feelings constitute our conscience.
And if we look backwards through our evolution, those feelings at some point cease to exist. I will come back to the conscience in a moment. But I also want to note that we had to evolve some way to police this reciprocal altruism situation. So in all human cultures, showing that it is innate behavior, we find the use of shame, ridicule, shunning, and gossip to spread the word on who is untrustworthy and to keep other people in line, just as described in the interview with Robin Dunbar.
Now, back to the conscience, because this is very relevant to the questions we began with. How can anyone with a conscience perpetrate the crimes I described—home invasions, especially with the attendant violence?
Evolutionary psychologists tell us that 30-40% of our ideas of right and wrong are the same, universally, across human cultures. So 30-40% of our conscience is genetic. But that leaves 60-70%, the major part, which is formed by our environment—by the conditions under which we are raised and what we are taught.
Evolution had to leave our consciences adaptable because in some situations it is more important to survival that we lie and cheat or even be violent instead of being virtuous. You can think about Nazi Germany as an extreme example.
But as we think about the origin of those crimes in Oakland we can all imagine that poverty produces this kind of situation also. If I can’t provide for myself or for my family, I will need to think differently about the right and wrong of lying, stealing, or even violence. It would be the same for any of us. So the human conscience is not what we have always imagined it to be—a mental system pointing us to the absolute right. It is an innate, evolutionary tool aimed at insuring our survival in a group based on reciprocal altruism. It makes us appear to be “good” and perform properly so that we can stay in the group. And it is tuned by our circumstances.
Of course, over the course of those 6 million years we also had to deal with the arrival of occasional people outside our “in group”, the stranger, the “other”. And judging by what we see as the natural reaction to outsiders in all human cultures, those people must have been pretty threatening to our survival. Because in all human cultures the natural feelings toward outsiders are distrust and suspicion, and the strategies we employ are often exploitation and even violence.
We see this everywhere today. We see it in anti-immigrant and anti-Muslim sentiment here and abroad. We see it in the attitude of some of the people of Lancaster, who want to eject everyone in Section 8 housing from their city. A small example is the treatment that my daughter experienced in 5th grade, when she wasn’t a member of the “popular group”, so she was an outsider. I’m sure many of us can relate to that, or went through it with our children.
But there are also much more serious examples like the attitude of one gang in Los Angeles or Oakland toward the gang in the next neighborhood—the other—or ethnic cleansing, or slavery. All of these shameful acts of our present and past are perpetrated by people we would call normal, not by sociopaths. That is a clue that this is innate behavior. This is our natural heritage, too—our innate feelings toward “the other”.
Can’t we be saved from this instinctive behavior by thinking? We are supposed to be the “thinking animal”.