Dunbar Number: 150 relationships

Source: Forbes, Jan 2013

The primary finding of the study, however, was a single number: the total population of the households each set of cards went out to. That number was 153.5, or roughly 150.

Over the past two decades, he 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.

For Dunbar, there’s a simple explanation for this: … most cannot maintain many more than 150 meaningful relationships. Cognitively, we’re just not built for it.

“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.

“What Dunbar’s research represents is that no matter how the march of technology goes on, fundamentally we’re all human, and being human has limits,” says Dave Morin, one of Path’s co-founders. To developers such as Morin, Dunbar’s insistence that the human capacity for connection has boundaries is a challenge to the ethos of Facebook, where one can stockpile friends by the thousands.

Dunbar’s research on how long the average friendship can survive in the absence of face-to-face contact (6 to 12 months), and about how, according to Dunbar, a woman can have two best friends (including her romantic partner), but a man only one.

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. Why, he isn’t sure.

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