The Dunbar Number

The Dunbar number refers to Robin Dunbar and his book How Many Friends Does One Person Need? Dunbar's Number and Other Evolutionary Quirks which was reviewed in the Los Angeles Review of Books. Dunbar is an anthropologist and evolutionary biologist who tries to explain our behavior by looking at the adaptations that have made us human.

One of Dunbar's points is the importance of family to survival. He ties together statistics on survival in extreme conditions like the Donner Party or the Pilgrims first winter to show that even old people and children in families survive better than even virile unattached young people. More benign stats show that  children in larger families tend to get sick less often than children in small families and that 76% of Americans rate family as the most important thing in their lives.

Not great news for a singleton like me, but Dunbar also looks at friendship networks as well as family. He suggests that our brain has evolved to be close to about 150 people including family and friends, about the size of most Neolithic villages and associations of interrelated hunter-gatherer bands. That 150 number is the Dunbar Number.  Dunbar suggests on average that we have 3-5 close friends we speak to at least weekly and about 10-15 more friends who we might not be in contact with as often but whose death would distress us. These inner circles can include relatives. The other 120 folks that the brain keeps in its rolodex are less close and can drop off the brain's list if connections aren't maintained. Dunbar also asserts that kinship links last longer than friendship links even if they aren't cultivated as often.  All of the above is about averages, by the way,  they don't account for people like Fran Ialenti who remember the names of every student, their parents, and grandparents. As George Carlin once said take a look at how dumb the average guy is and remember that half the people are dumber than that. Clearly, I exceeded my Dunbar number a long time ago no wonder I have trouble remembering names! Hooray, here's a time when I'm ecstatic to be in the lower half of the bell curve!

A couple of interesting points on my own. First, Dunbar's three levels of association certainly have some kind of connection to Aristotle's three levels of friendship. Wish I had Dunbar's research when we were talking about this in Philosophy class, but student discussions (even the Facebook generation) tend to confirm Dunbar's ideas. Second, the adaptation that leads to the Dunbar number, 150 associates before the neocortex starts to overload, is similar to the way our short term memory has evolved. Studies there show the brain is adapted to remembering a maximum of seven digits in short term memory. Ever get a phone number from 411 with no ability to write it down? If you can't offload the area code quickly as the familiar 508, you'll have a relatively hard time remembering it because it exceeds the seven digit limit. Finally, the Dunbar number of 150 is between the other anthropological magical numbers of 30 and 300. Th number 30 is about the size of the largest group of people anthropologists have found which doesn't need some kind of leader to function. Small hunter-gatherer bands of this size function with group discussion and total freedom of the individual to choose another path. At 300 human groups pass from relatively informal headman or headwoman systems to more formally organized governments. This too must have some relationship to the Dunbar number.