That evolution decreases the sacrifice of individual life to the life of the species, we may see on glancing upwards from the microscopic protozoa, where the brief parental life disappears absolutely in the lives of the progeny, to the mammalia, where the greatest conciliation of the interests of the species, the parents and the young, is displayed. The highest constitution of the family is reached where there is such conciliation between the needs of the society and those of its members, old and young, that the mortality between birth and the reproductive age falls to a minimum, while the lives of adults have their subordination to the rearing of children reduced to the smallest possible. The diminution of this subordination takes place in three ways: First, by elongation of that period which precedes reproduction; second, by fewer offspring born, as well as by increase of the pleasure taken in the care of them; and third, by lengthening of the life which follows cessation of reproduction. Let us bear in mind that the domestic relations which are ethically the highest, are also biologically and sociologically the highest. MARRIAGE The propriety of setting out with the foregoing purely natural-history view will be evident upon learning that among low savages the relations of the sexes are substantially like those common among inferior creatures. The effect of promiscuity, however, being to hinder social evolution, wherever it was accompanied by unions having some duration, the product of such unions were likely to be superior to others, and from this primitive stage domestic evolution takes place in several directions by increase of coherence and definiteness. From promiscuity we pass to that form of polyandry in which the unrelated husbands have but one wife; thence to the form in which the husbands are related; and finally to the form in which they are brothers only, as in the fraternal polyandry of the ancient Britons. It is almost needless to point out that, as in passing from promiscuity to polyandry the domestic relations become more coherent and definite, so do they in passing from the lower forms of polyandry to the higher. That polygyny is better than polyandry may be concluded from its effects. It conduces in a higher degree to social self-preservation than the inferioi types of marital relations by making possible more rapid replacement of men lost in war, and so increases the chance of social survival. By establishment of descent in the male line it conduces to political stability; and, by making possible a developed form of ancestor-worship, it consolidates society. MONOGAMY