There is a concept in cognitive psychology called the channel capacity, which refers to the amount of space in our brain for certain kinds of information. As human beings, we can only handle so much information at once. Partly its a question of time and energy. For example, to be someone's best friend requires a minimum investment of time and emotional energy. Caring about someone deeply is exhausting. At a certain point, somewhere between 10 to 15 people, we begin to overload.
Perhaps, the most interesting natural limit is what might be called our social channel capacity. The case for a social capacity has been made, most persuasively, by Robin Dunbar.
Over the past two decades, evolutionary psychologist Dunbar and other like-minded researchers have discovered groupings of 150 nearly everywhere they looked. Anthropologists studying the world’s remaining hunter-gatherer societies have found that clans tend to have 150 members. Throughout Western military history, the size of the company—the smallest autonomous military unit—has hovered around 150. The self-governing communes of the Hutterites, an Anabaptist sect similar to the Amish and the Mennonites, always split when they grow larger than 150. So do the offices of W.L. Gore & Associates, the materials firm famous for innovative products such as Gore-Tex and for its radically nonhierarchical management structure. When a branch exceeds 150 employees, the company breaks it in two and builds a new office.
For Dunbar, there’s a simple explanation for this: In the same way that human beings can’t breathe underwater or run the 100-meter dash in 2.5 seconds or see microwaves with the naked eye, most cannot maintain many more than 150 meaningful relationships. Cognitively, we’re just not built for it.
In general, once a group grows larger than 150, its members begin to lose their sense of connection. “The figure of 150 seems to represent the maximum number of individuals with whom we can have a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us,” Dunbar has written.
While Dunbar has long been an influential scholar, today he is enjoying newfound popularity with a particular crowd: the Silicon Valley programmers who build online social networks. At Facebook and at startups such as Asana and Path, Dunbar’s ideas are regularly invoked in the attempt to replicate and enhance the social dynamics of the face-to-face world. Software engineers and designers are basing their thinking on what has come to be called Dunbar’s Number.
As group size grows, a dizzying amount of data must be processed. A group of five has a total of 10 bilateral relationships between its members; a group of 20 has 190; a group of 50 has 1,225. Such a social life requires a big neocortex, the layers of neurons on the surface of the brain, where conscious thought takes place. To come up with a predicted human group size, Dunbar plugged our neocortex ratio into his graph and got 147.8.
Dunbar actually describes a scale of numbers, delimiting ever-widening circles of connection. The innermost is a group of three to five, our very closest friends. Then there is a circle of 12 to 15, those whose death would be devastating to us. (This is also, Dunbar points out, the size of a jury.) Then comes 50, “the typical overnight camp size among traditional hunter-gatherers like the Australian Aboriginals or the San Bushmen of southern Africa,” Dunbar writes in his book How Many Friends Does One Person Need? Beyond 150 there are further rings: Fifteen hundred, for example, is the average tribe size in hunter-gatherer societies, the number of people who speak the same language or dialect. These numbers, which Dunbar has teased out of surveys and ethnographies, grow by a factor of roughly three.
At Facebook itself, Dunbar still comes up often. “We do talk about it. In a lot of contexts it’s a compelling framing of some of the data that we have about people’s relationships,” says Cameron Marlow, a sociologist and the head of the company’s data science team.
A paper published in 2011 found that on Twitter the average number of other people a user regularly interacts with falls between 100 and 200. And though the limit on how many Facebook friends one can have is a generous 5,000, the average user has 190—more than 150, but within what Dunbar sees as the margin of error.
In smaller groups, people are a lot closer. If your group gets too large, you don't have enough things in common, you start to become strangers and that close-knit fellowship starts to get lost.
Sources: Bloomberg BusinessWeek, January 14, 2013
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