MOOT POINTS IN SOCIOL OGY 87
the farms. One consequence is that the city never becomes tradi- tional and static, as it might well do if it grew from its own loins. Another result is the gradual depletion of the eugenic capital of the rural population e. g., the increasing brachycephaly of France within historic times owing to the continual drain of its best elements to the cities. As the towns draw from the fields, so the fertile valleys, sterilized by their very prosperity, draw from the barren uplands streams of migrants representing the peoples beaten in ancient conquests.
It may happen that the distinct types in the population the martial and the industrial, the imaginative and the calculating, the " ideo-motor " and the "critical-intellectual " come under diverse influences which make their rates of reproduction unequal, and so change their numerical proportions. Every such shifting of the predominant type is marked by important vicissitudes in society.
The unequal increase of population on the opposite sides of a frontier finally sets up a current of migration which replaces one race, language, or civilization by another, thereby entailing changes in society. If the frontier is a political one, the movement is likely to take the form of an armed invasion, and the society must sustain the shock of war. It is now understood that the assaults of the Germans upon the Roman empire were prompted by over- population, and the eventual failure to withstand them was due to the fact that infecundity had reduced the empire to a hollow shell.
II. The accumulation of wealth. The progress of wealth, and the expansion of income which attends the control of a growing mass of capital, have a transforming effect on society. Even a general movement of prosperity shared in by all is a dynamic factor. The enlarged production shows itself, not along the entire line of commodities, but chiefly in the higher grades of goods, and in comforts and luxuries. These qualitative changes in production cannot but result in the transfer of labor and capital from certain occupations to others, from extractive to elaborative industries, from the production of goods to the sup- plying of services, from certain centers and regions to other
