Size (the number of people involved) is an important characteristic of the groups, organizations, and communities in which social behavior occurs.
As an organization or community grows in size it is apt to experience tipping points where the way in which it operates needs to change.
An infant requires a caregiver in order to survive, so life begins in a pair relationship that is apt to influence later ones.
Pair relations can be trivial and fleeting (like that of a clerk and customer at a checkout stand) or multi-purpose and enduring (like a lifelong marriage).
We are comfortable in dealing with someone who is similar to ourselves, and any two persons can usually find common traits or experiences to serve as "hook up points" between them.
She can fix the lawn mower and he is a good cook; Gilbert writes the book and Sullivan composes the music.
[3] Where polygamy is practiced, a husband taking a second wife will often provide her with separate quarters so as to have two pair relationships instead of a contentious household of three adults.
A similar but short-lived pattern occurs at cocktail parties: studies of social gatherings find frequent clusters of one person talking and three listening.
[4] As the size of a group increases: Many human activities are too big, difficult, or complex to be accomplished by a single person.
At the same time, they may require such close coordination that if more than, say, a half dozen persons try to collaborate they get in each other's way, lose a common focus, and tend to work at cross purposes.
Our species has depended largely on subsistence provided by collaboration among members of the immediate family: a woman who bears, nurses, and looks after children (with aid and advice of her mother), and does chores consistent with those responsibilities; a man, who is free to range farther from the home base for food and materials and can do things that require extra strength or concentration; and the children providing whatever assistance is required of them as they grow more capable.
At about that size there is no longer enough time at meetings to hear from everyone, and participants can't be seated so that they can easily see and listen to each other.
Dunbar's number is based on studies of social animals, which have shown a correlation between the typical frontal brain capacity the members of a species and the maximum size of the groups in which they live.
In a small church the minister typically knows everyone, and the congregation is “one big family.” It is not easy to grow beyond 150 members, however, because that requires (besides a bigger building) augmenting the minister with paid staff, systematically recruiting and training volunteers, and dealing with increased numbers and diversity by developing specialized groups and programs.
Educators are advocating subdividing large schools into smaller units so that staff can know all the students and there will be more feeling of belonging, support and continuity.
It has been observed that the population of a city is roughly inversely proportional to its rank in size among the urban areas of its economic region (Zipf's law).