The "infant mortality movement" also has an effect here which is rarely recognized. It is a stock argument of birth control propagandists that a high birth-rate means a high rate of infant mortality; but A. O. Powys has demonstrated that cause and effect are to some extent reversed in this statement, and that it is equally true that a high rate of infant mortality means a high birth-rate, in a section of the population where birth control is not practiced. The explanation is the familiar fact that conception takes place less often in nursing mothers. But if a child dies early or is bottle-fed, a new conception is likely to occur much sooner than would otherwise be the case. By reducing infant mortality and teaching mothers to feed their babies naturally, the infant mortality movement is thereby reducing the birth-rate in the poorer part of the population, a eugenic service which to some extent offsets the dysgenic results that, as we shall show in the last chapter, follow the "Save the Babies" propaganda. With the spread of the birth control and infant mortality movements one may therefore look forward to some diminution of the differential element in the birth-rate, together with a further decline in that birth-rate as a whole. Such a situation, which seems to us almost a certainty within the next decade or two, will not change the duty of eugenics, on which we have been insisting in this chapter and, to a large extent, throughout the present book. It will be just as necessary as ever that the families which are, and have been in the past, of the greatest benefit and value to the country, have a higher birth-rate. The greatest task of eugenics, as we see it, will still be to find means by which the birth-rate among such families can be increased. This increase in the birth-rate among superior people must depend largely on a change in public sentiment. Such a change may be brought about in many ways. The authority of religion may be invoked, as it is by the Roman Catholic and Mormon churches[127] whose communicants are constantly taught that fecundity is a virtue and voluntary sterility a sin. Unfortunately their appeal fails to make proper discriminations. Whatever may be the theological reasons for such an attitude on the part of the churches, its practical eugenic significance is clear enough.