In so doing it will certainly tend also to destroy prostitution, which is simply one of the forms in which the merging of sexual selection in natural selection has shown itself. Wherever sexual selection has free play, unhampered by economic considerations, prostitution is impossible. The dominant type of marriage is, like prostitution, founded on economic considerations; the woman often marries chiefly to earn her living; here, too, we may certainly expect profound modifications. We have long sought to preserve our social balance by placing an unreasonable licence in the one scale, an equally unreasonable abstinence in the other; the economic independence of women, tending to render both extremes unnecessary, can alone place the sexual relationships on a sound and free basis. The State regulation of marriage has undoubtedly played a large and important part in the evolution of society. At the present time the advantages of this artificial control no longer appear so obvious (even when the evidence of the law courts is put aside); they will vanish altogether when women have attained complete economic independence. With the disappearance of the artificial barriers in the way of friendship between the sexes and of the economic motive to sexual relationships--perhaps the two chief forces which now tend to produce promiscuous sexual intercourse, whether dignified or not with the name of marriage--men and women will be free to engage, unhampered, in the search, so complicated in a highly civilized condition of society, for a fitting mate.[49] It is probable that this inevitable change will be brought about partly by the voluntary action of individuals, and in greater measure by the gradual and awkward method of shifting and ever freer divorce laws. The slow disintegration of State-regulated marriage from the latter cause may be observed now throughout the United States, where there is, on the whole, a developing tendency to frequency and facility of divorce. It is clear, however, that on this line marriage will not cease to be a concern to the State, and it may be as well to point out at once the important distinction between State-_regulated_ and State-_registered_ marriage. Sexual relationships, so long as they do not result in the production of children, are matters in which the community has, as a community, little or no concern, but as soon as a sexual relationship results in the pregnancy of the woman the community is at once interested. At this point it is clearly the duty of the State to register the relationship.[50]