150, 50, 15, 5. Those are the magic numbers in the sociology of friendship, according to University of Oxford professor Robin Dunbar. 150 is the number of casual friends an average person has. From there, we tend to have 50 people we classify as close friends, meaning we would invite them to a group dinner. 15 is the number of friends (and family) we can count on for sympathy and to whom we can disclose most things. 5 people represent our core support group, often composed partly of family members--we call these people our best friends.

The outer limit on human social groups stands at about 1,500, representing the maximum number of people we can identify correctly by putting a name to a face. So what about those who boast more than 1,500 friends on Facebook? Have social media extended our capacity to be friends with others? That's unlikely, says those who follow Dunbar's research:

"With social media, we can easily keep up with the lives and interests of far more than a hundred and fifty people. But without investing the face-to-face time, we lack deeper connections to them, and the time we invest in superficial relationships comes at the expense of more profound ones."

In his Big Think interview, physician and sociologist Nicholas Christakis argues that who we count among our circle of friends partly determines our own behavior. This is due to the natural tendency of humans to mimic one another. So who do you mimic? And why?

Read more at the New Yorker

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