For the preservation of the individual the great needs are for food and shelter from the elements; shelter means clothing as well as a habitation. Man's want for these things impels him to "get a living." It starts the organization of societies in the form of industrial and business enterprises. It develops a system of exchange of goods for goods and of goods for services, with some one commodity to serve as a medium of exchange and a measure of values. The scientific study of this phase of human activity is the special province of political economy or economics; but here again sociology must select and interpret in its own way.