The demographic properties of a population include such things as its size, its density, how it is dispersed or concentrated (e.g., to what extent its members are concentrated in a few areas or spread out more evenly over its entire territory), the patterns of migration into and out of the society, its compostion in terms of age and sex, and its birth and death rates.  These characteristics, like certain clusters of genes, vary from one society to another.  But these variations, unlike most genetic variations, have direct, demonstable, and far-reaching consequences for human societies (1991, p. 29).