You may have thousands of Twitter followers, but how many of them could you call a friend, or even an acquaintance?
About twenty years ago, the British anthropologist, Robin Dunbar, observed an association between the sizes of primate brains--specifically the size of the neocortex--and the number of social contacts. Chimps can process a smaller number of contacts than humans. Dunbar concluded that humans can handle regular contact with a number of friends somewhere between 100 and 200, and 150 became the standard Dunbar number for our species.
Dunbar went on to say that this number has held up reasonably throughout human history. For example, he predicted that prehistoric hunter-gatherer groups would split when they surpassed 150 individuals in size, based on observations that contemporary hunter-gatherer groups approximate that number, as well as other grouping such as academic subspecialties or working groups within corporations.
The TV show Cheers preceded Dunbar's work, but he would agree that a bar in which "everyone knows your name" could not exceed 150 patrons.
A recent study from Bruce Goncalves and associates at Indiana University appears to demonstrate that even with the great reach of a tool like Twitter, we are still bound to the original Dunbar number, 150. ("Validation of Dunbar's number in Twitter conversations," by Bruno Goncalves, Nicola Perra, and Alessandro Vespignani, http://arxiv.org/PS_cache/arxiv/pdf/1105/1105.5170v1.pdf)
Goncalves and his associates note that "biological constraints on social interaction go along with other real-world physical limitations. After all, a person's time is finite and each person must make her own choices about how best to use it given the priority of personal preferences, interests, needs, etc."
They wondered whether "microblogging tools facilitate the way we handle social interactions and that this results in an online world where human social limits are finally lifted, making predictions such as the Dunbar's number obsolete." But they also wondered whether the biological constraints of our neocortex would make tools such as Twitter "analogous to a pocket calculator that, while speeding up the way we can do simple math, does not improve our cognitive capabilities for mathematics."
To tease this out, they were able to study 3 million Twittter users and their 380 million tweets over a 4-year period.
Sounds like a multitude of contacts, far more than the measly 150 Dunbar number.
But the researchers didn't accept a mere Twitter follower as a friend or social contact. When they set up a criterion that required a tweet to be requited--that is, a two-way conversation, they found that users became overwhelmed when they had to keep up with more than 150 followers, and that the Dunbar number held up reasonably well.
Just as a calculator doesn't make us better at math, Twitter doesn't make it any more possible to have more than 150 social contacts.
As they put it, "even in the even in the online world cognitive and biological constraints holds as predicted by Dunbar's theory limiting users' social activities."
So biology remains destiny when it comes to friendship.
I wonder, too, what relationship there might be between the Dunbar number and Stanley Milgram's Small World Hypothesis. More than fifty years ago, Milgram wondered about the chances that any two randomly selected people would know each other. He picked out random people in Kansas, and sent them a letter with a name of a person in Massachusetts. The recipients were asked either to send them directly to the Massachusetts target--if they knew the person--or to forward them to any acquaintance who might possibly know the person. On average, among those who chose to participate, an average of 5.5 contacts connected the randomly connected people. Rounded up, that became the famous Six Degrees of Separation.
The precise relationship between Six Degrees of Separation and the Dunbar Hypothesis--if there is one--remains to be determined, but Disney may have been right, "It's a small world, after all."
My book, Nasty, Brutish, and Long: Adventures In Eldercare (Avery/Penguin, 2009), was a Finalist for the 2010 Connecticut Book Award. Click here to read the first chapter It provides a unique, insider's perspective on aging in America. It is an account of my work as a psychologist in nursing homes, the story of caregiving to my frail, elderly parents--all to the accompaniment of ruminations on my own mortality. Thomas Lynch, author of The Undertaking, calls it "A book for policy makers, caregivers, the halt and lame, the upright and unemcumbered: anyone who ever intends to get old."