If the smallest community has historically consisted of between 12 and 36 members, is there a limit to the maximum size of a community?
One factor that might limit the maximum size is possible awareness by each member of the community of every other member of the community. Awareness depends on two variables: speed of communication and speed of information processing by each individual. The minimum speed of communication would be one message in a useful interval of time, and the message would need to be comprehensible. The maximum number of people that could be sensed by a member, subject to these constraints, would therefore be the maximum population of the community.
For a useful interval, one year seems like a reasonable guess. Natural processes and activities that humans have mostly relied on for survival tend to cycle over this period. For example, the seasons affect agriculture, and businesses key their activities on transactions that occur over the course of a fiscal year. One year is also the amount of time a human could travel a distance equal to the world’s circumference at speeds attainable on foot.
We know from psychology that people can comprehend no more than seven things per second. If those “things” were pieces of information representing other people, then a person could be aware of no more than seven people per second. Over the course of a year, the maximum number of people in a community is therefore seven times the number of seconds that an average member can receive a message. If all 24 hours each day were available, the maximum community size would be 221 million people; this compares well with estimates of the world’s population at the beginning of the Christian era when the Roman Empire was at its peak.