Looking at the course of history widely, we may see, then, in the differentiation of social classes by the social ladder and in the tendency of the upper strata to fail to reproduce themselves, an explanation of the cyclic course of civilisation. This has been ascribed by some authors[137] to race-crossing, followed by blending, and ultimately by stagnation consequent upon complete blending and the flowering period which coincides with it. But we now have a more adequate explanation of the decay which follows upon the blooming period. It is not mere stagnation, resulting from the achievement of social harmony and the relaxation of efforts at social adaptation and achievement of all kinds. The decline is probably due as much, and perhaps in a much higher degree, to the exhaustion of the mass of the population, the completion of the draining process by which, throughout the whole period of the development of the cycle of civilisation, the best elements and strains have been drained off from the lower strata, brought to the top, and strained off. It is interesting to speculate on the possible effect on this process of the fact that we are becoming more clearly conscious of these tendencies and subjecting them to scientific inquiry. Already the legislature has taken one small step of a eugenic nature and is soon to take another. The important thing is that we should recognise that men are not the helpless sport of blind forces, that mankind can control its own destiny in ever increasing degree as knowledge grows. A word may be said in regard to sexual selection, which probably played a part in the evolution of the mental capacities of men. It would seem that, in the peoples among whom monogamy is the rule, it no longer operates to any appreciable degree. With the general excess of females, we could suppose that it still tended to race improvement only if the unmarried women were on the whole distinctly inferior to the married. But, if there is any difference, it is probably the other way; because the most able women are more and more attracted into independent careers. The further the so-called emancipation of women goes, the more will this be the case. Civilisation, then, tends from the first to put an end to that elimination of the less fit individuals by the severities of Nature which we call natural selection; and, as soon as it has passed beyond its earliest stages, it brings to an end also the mortal conflicts of social groups and the consequent group selection, which was in all probability a main factor of racial progress in the prehistoric period. It abolishes also at an early stage the improving influence of sexual selection, which was probably the third principal condition of the development of the higher powers of mankind.