It is the principle of survival-value that explains the dominance of monogamy at all stages of human society--with the single exception of continuously and wholly militant societies, in which polygamy obtained in consequence of the great numerical excess of women. It is the fate of the children, in which everything is involved, that has determined the history of human marriage. Furthermore, we may see here one more illustration of the truth that quality is ousting quantity in the course of progress, and that a low birth-rate represents a more advanced stage than a high birth-rate. The birth-rate under polygamy is undoubtedly high, but polygamy does not make for the survival and health of the children, and the infant mortality is gigantic. As I have said elsewhere, “the form of marriage which does not permit the babies to survive, _they_ do not permit to survive. There is the beginning and the end of the whole matter in a nutshell. It is not a question of the father's taste and fancy, but of what he leaves above ground when the worms are eating him below.... No system yet conceived can compare for a moment with monogamy in respect of the one criterion which time and death recognise, the fate of the children.” In a word, the wholly adequate and only possible explanation of the historical fact of the dominance of monogamy is its supreme survival-value. It has competed with every other kind of sex relation and has been selected by natural selection because of its supreme service for race-culture--the most perfect conceivable addition of fatherhood to motherhood. =Plato and motherhood.=--Thus eugenics must repudiate not only the ideas of Mr. Shaw on this subject, but the teaching of Plato, from whom Mr. Shaw's ideas on this particular subject are apparently derived. It is in the fifth book of his _Republic_ that the pioneer eugenist lays down his ideas for race-culture. He realised, indeed, the importance, after birth, of the nurture of children--“it is of considerable, nay, of the utmost importance to the State, when this is rightly performed or otherwise;” and he refers also to their nurture while very young, “in the period between their generation and their education, which seems to be the most troublesome of all.” His method involved a complete community of wives and children amongst the guardians of the State, and on no account were the parents to know their own children nor the children their parents. The best were to be chosen for parents, on the analogy of animal race-culture by man. The children of inferior parents were to be killed. The others were to be conveyed to the common nursery of the city, but every precaution was to be taken that _no mother should know her own child_. This practice was to be the cardinal point of the Republic and “the cause of the greatest good to the city.”