We get an insight from the field studies of anthropologists:
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.
Here, a British anthropologist, Robin Dunbar, makes an interesting case for social capacity—that is, the maximum number of people and things with which the human brain can cope effectively. Primates like monkeys, chimpanzees, baboons, and human beings, he observes, have the largest brain capacities of all mammals. And the neocortex—the part of the brain that deals with complex reasoning—is a lot larger in primates than in other mammals. Of all primates, humans socialize in the biggest groups, because only the human neocortex is of the right size. That right size, however, turns out to be far smaller than the size of most modern organizations. Dunbar has got it down to a formula. He claims that in the human primate the ratio of the size of the neocortex to the brain as a whole can tell him the maximum size of the group with which the human primate can best network. In humans that number is 147.8 or, approximately, 150.
Dunbar says anthropology yields dozens of examples of this magic number. In 21 different hunter‐gatherer cultures ...