Science, when it has once acquired a firm hold upon social organization, is hardly likely to stop short at those biological aspects of human life which have hitherto been left to the joint guidance of religion and instinct. We may, I think, assume that both the quantity and the quality of the population will be carefully regulated by the State, but that sexual intercourse apart from children will be regarded as a private matter so long as it is not allowed to interfere with work. As regards quantity, the State statisticians will determine as carefully as they can whether the population of the world at the moment is above or below the number which leads to the greatest material comfort per head. They will also take account of all such changes of technique as can be foreseen. No doubt the usual rule will be to aim at a stationary population, but if some important invention, such as artificial food, should greatly cheapen the production of necessaries, an increase of population might for a time be thought wise. I shall, however, assume that, in normal times, the world government will decree a stationary population.