_Checks more Effective as Wealth Increases._--It is clear that the dominant motives which restrain the growth of population act more powerfully on the well-to-do classes than on the poor. The need of invested wealth, the need of education, the determination to adhere to a social standard of comfort and to avoid losing caste, are stronger in the members of the higher classes than in those of the lower ones, and become more dominant in the community as more and more of its members belong to the upper and the middle classes. _Immediate Causes of a Slow Increase of Population._--The economic motive for a slow growth of population can produce its effect only as it leads to some line of conduct which insures that result. Means must be adopted for attaining the end desired, and when one looks at some of the means which are actually resorted to, he is apt to get the impression that an indispensable economic result is in some danger of being attained by an intolerable moral delinquency. Must the society of the future purchase its comforts at the cost of its character? Clearly not if the _must_ in the case is interpreted literally. A low birth rate may be secured, not at the cost of virtue, but by a self-discipline that is quite in harmony with virtue and is certain to give to it a virile character which it loses when men put little restraint on their impulses. Late marriages for men stand as the legitimate effect of the desire to sustain a high standard of living and to transmit it to descendants; and late marriages for women stand first among the normal causes of a retarded growth of population. Moreover, the same moral strength which induces men to defer marriage dictates a considerate and prudent conduct after it, and prevents unduly large families without entailing the moral injury which reckless conduct involves. On the other hand, there may be an indefinite postponement of marriage by classes that lack moral stamina and readily lapse into vice. There are vicious measures, not here to be named in detail, which keep down the number of births or increase the number of deaths, mostly prenatal, though the infanticide of earlier times is not extinct. By strength and also by weakness, by virtue and also by vice, is the economic mandate which limits the rate of growth of population carried out. A limit of growth must be imposed if mankind is to make the most of itself or of the resources of its environment. There is no great doubt that it will be so imposed, and the great issue is between the two ways of doing it; namely, that which brutalizes men and depraves them morally and physically, and that which places them on a high moral level.