The Facebook movie is upon us. "The Social Network" was directed by David Fincher ("Fight Club") and written for the screen by Aaron Sorkin ("The West Wing"), and by all accounts it's among the best work either has done. The review aggregating site Metacritic has it with a pretty staggering Metascore of 97 out of 100.
The film is about the founding of the social networking-cum-world conquering site Facebook, which currently boasts over 500 million users around the world, most likely including you. Fincher and Sorkin’s version of the story has the site’s founder, Mark Zuckerberg, making quite a few enemies for himself on his way to helping us all make more friends. So, is it working? Is it useful? Really, how many friends does one person need?
150.
That’s not me talking. That’s evolution.
The number 150 has come to be accepted as the limit to the number of individuals with whom any one person can maintain stable relationships. You may know it as “Dunbar’s Number,” named for Robin Dunbar, anthropologist, evolutionary biologist, and Professor of Psychology at the University of Liverpool. Dunbar describes the figure as the upper limit to the number of people with whom humans can actually form relationships strong enough to rely on. Put another way, it’s the circle of people who will do you a favor. We simply don’t have the cognitive capacity to maintain a greater number of relationships at the level of complexity required for a bond to be “real.”
Dunbar arrived at the number by working outwards from the social intelligence theory of why primates have such large brains. The theory holds that the complex social world in which primates live spurred the evolution in brain size. Basically, primates are more dependent on their social bonds than other types of animals, and those bonds are also more complex and socially informed. This hypothesis, according to Dunbar and others, is supported by a strong correlation between the size of a group (and hence its social complexity) and the relative size of the neocortex. Dunbar examined these correlations, plotted the sizes of various primate brains against the sizes of their social groups, determined the relationship, plugged in the size of the human brain, and got 150.
"Our social world is still what it was several hundred thousand years ago," he says. "The number of people we know personally, whom we can trust, whom we feel some emotional affinity for, is no more than 150. It has been 150 for as long as we have been a species. And it is 150 because our minds lack the capacity to make it any larger."
It’s not just a theoretical shot in the dark, though. As Dunbar explains of this evolutionary magic number: “Once you start to look for them, groups of this size turn up everywhere.” In most modern armies, for example, the smallest independent unit is the company, which, including command and support staff, numbers roughly 130-150. The great success of the GoreTex company, as detailed by Malcolm Gladwell, relied on its founder’s insistence on creating completely separate factory units of about 150 workers each, rather than just expanding each factory. Neolithic villages from the Middle East, based on the number of dwellings, seem to have contained 120-150 people. And, according to stats available on the site, the average Facebook user has 130 friends.
Much has been hypothesized and bemoaned about the difference between online and real life friends, and the absurdity of friend counts in the thousands. Dunbar, to be sure, doesn’t say these online relationships are necessarily a bad thing. In fact, he says, they allow you to prevent “real” relationships from decaying over time. But relationships aren’t sustainable through Facebook alone. If you don’t go to the pub together, Dunbar says, that relationship will eventually drop out of your 150.
Dunbar’s most recent book, available now, is a collection of essays titled – ta da! – How Many Friends Does One Person Need? The book explains such evolutionary miscellanea as why monogamists need big brains, why it’s worth buying a new suit for an interview, and how to interpret a singles ad. Behavioral evolution makes good copy, people.
