How many people does it take to need a government? At what point does a crowd need crowd control?
I think attention is the key. In pairs, each member can give virtually full attention to the other. Nobody is ever more careful to act in the larger interest than someone who feels as if he or she is being watched. The need for governing is virtually nil in a pair. In small groups there is a bit more freedom from watching and being watched.
We don’t watch everyone, and we don’t feel like we are being watched all the time. There is generally a need for a familial sort of governing at this level; parents, den mothers, teachers and coaches can handle the governing at this level.
As groups get larger, the sense of watchfulness dissipates, at a similar ratio to the sense of being watched. There is a critical mass point in there somewhere where individuals lose personal interest in the group as a whole, and concentrate on only the parts of the group that they deal with directly.
There is another critical mass point where individuals begin to feel as if nobody is watching them, and they lose the shame that keeps them from acting against the group’s interest. At this point there is a need for governance, to replace individual watchfulness and apply shame to the unwatched.