Dunbar then decided to go beyond the existing evidence and into experimental methods.
In one early study, the first empirical demonstration of the Dunbar number in action, he and the Durham University anthropologist Russell Hill examined the destinations of Christmas cards sent from households all over the U.
In the process of figuring out the solution, he chanced upon a potentially far more intriguing application for his research.
Companies, in turn, tended to be broken down into smaller units of around fifty then further divided into sections of between ten and fifteen.
At the opposite end, the companies formed battalions that ranged from five hundred and fifty to eight hundred, and even larger regiments.
For the last twenty-two years, Dunbar has been “unpacking and exploring” what that number actually means—and whether our ever-expanding social networks have done anything to change it. The best known, a hundred and fifty, is the number of people we call casual friends—the people, say, you’d invite to a large party.
(In reality, it’s a range: a hundred at the low end and two hundred for the more social of us.) From there, through qualitative interviews coupled with analysis of experimental and survey data, Dunbar discovered that the number grows and decreases according to a precise formula, roughly a “rule of three.” The next step down, fifty, is the number of people we call close friends—perhaps the people you’d invite to a group dinner.