The Tipping Point: How Little Things Can Make a Big Difference

by Malcolm Gladwell

Dunbar has actually developed an equation, which works for most primates, in which he plugs in what he calls the neocortex ratio of a particular species—the size of the neocortex relative to the size of the brain—and the equation spits out the expected maximum group size of the animal. If you plug in the neocortex ratio for Homo sapiens, you get a group estimate of 147.8—or roughly 150. “The figure of 150 seems to represent the maximum number of individuals with whom we can have a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us. Putting it another way, it’s the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar.”