Growth and Development of Social Groups 
attracted little attention and which we are rewriting4. In it 
we added the concept of Rites of Intensification, in which 
whole groups of people conduct rituals together to allay dis- 
turbances due to external forces, such as war, weather, and 
seasonal change. 
As early as 1935 George Zipf demonstrated’ that the length 
of words in a language are, other things being equal, a function 
of their frequency of use, and in 1948 I showed, in a study of 
the Albanian Ghegs, that the ideal choice of a marital partner 
is the one that will cause the least possible disturbance to all 
persons concerned, including of course the kinfolk of the bride 
and groom, and not just the marital partners, who have little 
to say about it. 
These illustrations have shown that the equilibrium of a 
social group seems to follow the law of least effort, in a mathema- 
tically simple manner, apparently more nearly comparable to 
the ways in which equilibria are maintained in physics than in 
biology. Our societies seem to be simpler than we are. 
Before trying to define the term “‘social group”’, we first 
need to consider the definition of one of its components, the 
institution, a word of many meanings used here in the sociological 
sense. To quote from my own Reader in General Anthropology®: 
“in its simplest form an institution is a group of people who 
meet together in isolation often enough, regularly enough, and 
long enough each time, to do something together intensely 
enough and emotionally enough so that as a separate entity 
the group builds up its own set of rules, its own equilibrium, 
and its own structure.” 
In every society each individual belongs to more than one 
institution because a biological family is an institution and 
every viable social group includes more than one simple family. 
A social group is, therefore, a collection of human beings who 
habitually interact with each other more than they do with 
outsiders, and form, in a sense, a population. 
The most primitive peoples alive, who hunt and collect their 
food, live in breeding units of about three or four hundred 
individuals, and these units are also biological populations. At 
ra 
