The problem is one which applies to the whole of Western civilization. There is no difficulty in discovering a theoretical solution, but there is great difficulty in persuading men to adopt a solution in practice, because the effects to be feared are not immediate and the subject is one upon which people are not in the habit of using their reason. If a rational solution is ever adopted, the cause will probably be international rivalry. It is obvious that if one State—say Germany—adopted a rational means of dealing with the matter, it would acquire an enormous advantage over other States unless they did likewise. After the war, it is possible that population questions will attract more attention than they did before, and it is likely that they will be studied from the point of view of international rivalry. This motive, unlike reason and humanity, is perhaps strong enough to overcome men’s objections to a scientific treatment of the birth-rate. In the past, at most periods and in most societies, the instincts of men and women led of themselves to a more than sufficient birth-rate; Malthus’s statement of the population question had been true enough up to the time when he wrote. It is still true of barbarous and semi-civilized races, and of the worst elements among civilized races. But it has become false as regards the more civilized half of the population in Western Europe and America. Among them, instinct no longer suffices to keep numbers even stationary. We may sum up the reasons for this in order of importance, as follows:— 1. The expense of children is very great if parents are conscientious. 2. An increasing number of women desire to have no children, or only one or two, in order not to be hampered in their own careers. 3. Owing to the excess of women, a large number of women remain unmarried. These women, though not debarred in practice from relations with men, are debarred by the code from having children. In this class are to be found an enormous and increasing number of women who earn their own living as typists, in shops, or otherwise. The war has opened many employments to women from which they were formerly excluded, and this change is probably only in part temporary.