Welcome to Dunbar's Number

There's a number for circles, there's a special ratio for rectangles, and there are all sorts of scientific constants out there in the world but did you know there is also a number for human society as well?

Ever wonder how many people can work together toward one cause effectively? Or how many friends you can really have? How about before cars and telephones, how many people could you actually know and interact with? Did our ancestors, the Neanderthals, move in groups of 10 or 1000?

Dunbar's number is all about this theoretical biological maximum number of people that can be together. People have interpreted this in many ways, number of people in a town, number of people in a company actually working, or even the number of people that one can actually care for.

So what exactly is that number?