porportion of females among the negroes is about 4 per cent. greater than it is among the whites. The influence of this disparity on the figures of the whole population may be detected in Table VI., where the seven states with largest proportion of females in their cities are those which have a considerable negro population.
The argument to this point may be summarized as follows: (1) the proportion of the two sexes at any place and time is regulated by biological and social forces acting in cooperation; (2) immigration is an insufficient explanation of that proportion in the United States; (3) in all the various elements of the population the females show a tendency to concentration in the cities; (4) this tendency to dissociation of the sexes and concentration of the females in the cities is less marked among the native whites than it is among the negroes of the South and the immigrants of the North.
The preponderance of females in cities, when it has been noticed at all, has usually been accounted for in the same way in which the excess of males in this country has been explained. Women, it is said, find in cities greater opportunities for partial or entire self-support, and the scope for employment afforded them by country life is much less. Hence they remain in or migrate to the cities. This explanation is supported by the fact already shown, that immigrant and negro women, who are somewhat more likely to be dependent on their own resources for support, are more attracted to the cities than are the native whites. On the other hand the inadequacy of migration as an explanation of the preponderance of males in the whole country raises a doubt whether it is adequate to explain the excess of females in our cities. It is probable that in both cases migration has cooperated with those biological causes which establish and maintain approximately constant differences between the birth-rates and also between the death-rates of the two sexes. Unfortunately, our lack of information regarding the birth-rates and the death-rates in the United States makes it impossible to test this statement. But an illustration will make clear the
