Primates have huge brains. And one part of the brain, the neocortex, is remarkably larger in primates than in every other mammal. The neocortex handles complex thought and reasoning.
The neocortex as a percent of total brain volume varies widely, even among primates. For a while, it was thought that that was because some primates were just “smarter” than others, or the ones who had learned to use tools had developed that part of their brain. It turns out that the proportionate size of the neocortex is most closely correlated with the number of other primates you know personally.
Robin Dunbar, an anthropologist and evolutionary biologist postulates that because managing relationships is an extremely complex skill, the larger the group you live in, the larger the neocortex you require. Think about it – if you are in a group of 4, you have 6 relationships to keep track of: the 3 you have with the others, and the 3 they have with each other. If you live in a group of 20, there are 190. So Mr. Dunbar crunched some numbers, and it turned out he’s right – for 38 types of primates, there is a high degree of alignment between the “neocortex ratio” and the size of communities those species tended to form.
So what happens when you run the neocortex ratio on Homo sapiens? You get 147.8, which is commonly rounded to 150 and called, “Dunbar’s Number.” There are plenty of examples where this has proven out – the size of prehistoric villages and primitive, remote villages today. The Hutterites religious sect splits its communities when they reach 150. Gore Associates, the company that makes Gore-Tex, always builds a new plant when the employees in one get to 150. None of these things happen because they read about the Dunbar Number, it just “feels” right.
Up to 150 people, you can know everyone in the group, and even have a pretty good idea about how each of them feels about the others. Beyond that, it’s too much, so people develop smaller groups — they become literally divisive.
So, shoot for 150 regular customers when you plan your bar. If you start to get more than that, either make the club more exclusive, or open another location.