All the elements of society are conserved in its physical basis, the social population. With a study of population . . . the descriptive analysis of society must begin.

In the study of population on its physical side the facts of aggregation or grouping are the first to claim attention. The distribution of animal and human life over the surface of the earth is no uniform dispersion of solitary individuals. With few exceptions, living beings are disposed in groups which here are loose and scattered, and there are massed in dense aggregations. Some degree of aggregation is the indispensable condition to the evolution of society. ... - Giddings, Principles of Sociology, p. 79.