Natural selection, which is the central doctrine of Darwinism, has been explained as the "survival of the fittest." On this process has depended the progress observable throughout organic nature to which the term evolution is applied; for, although there has been from time to time degradation, that is, a retrogression, this has had relation only to particular forms, organic life as a whole evidencing progress towards perfection. When man appeared as the culmination of evolution under terrestrial conditions, natural selection would seem almost to have finished its work, which was taken up, however, by man himself, who was able by "artificial" selection to secure results similar to those which Nature had attained. This is true especially in relation to animals, the domestication of which has always been practiced by man, even while in a state of nature. Domestication is primarily a psychical process, but it is attended with physical changes consequent on confinement and variation in food and habits. This alone would hardly account, however, for the great number of varieties among animals that have been long domesticated, and it is probable that actual "stirpiculture" has been practiced from very early times. This term is derived from the Latin _stirpis_, a stock or race, and _cultus_, culture or cultivation, and it means, therefore, the cultivation of a stock or race, although it has come to be used in the sense of the "breeding of offspring," and particularly of human offspring. It is evident, however, that in relation to man this is too restricted a sense, and it must be extended so as to embrace as well the rearing and training as the breeding of children, in fact, _cultivation_ in its widest sense, in which is always implied the idea of improvement. Stirpiculture in this extended sense was not unknown to the ancients, both in theory and in practice. As to the former, the most noted example is that of Plato, who, in his "Republic," proposed certain arrangements as to marriage and the bringing up of children which he thought would improve the race, and hence be beneficial to the State. The State was to Plato all in all, and he considered that it should form one great family. This idea could not be carried into effect, however, so long as independent families existed, and therefore those arrangements had for one of their chief aims the abolition of what we regard as family life. This Plato thought was the best for the State, and the advantage which was supposed to accrue to it by the absence of separate families is expressed in a marginal note, which says: "There will be no private interests among them, and therefore no lawsuits or trials for assault or violence to elders."