On the subject of artificial social constructions, the socialists might say to the individualists: let him who is without sin, cast the first stone. The true reply is wholly different. Scientific socialism represents a much more advanced phase of socialist thought; it is in perfect harmony with modern, experiential science, and it has completely abandoned the fantastic idea of prophesying, at the present time, what human society will be under the new collectivist organization. What scientific socialism can affirm and does affirm with mathematical certainty, is that the current, the trajectory, of human evolution is in the general direction pointed out and foreseen by socialism, that is to say, in the direction of a continuously and progressively increasing preponderance of the interests and importance of the species over the interests and importance of the individual--and, therefore, in the direction of a continuous _socialization_ of the economic life, and with and in consequence of that, of the juridical, moral and political life. As to the petty details of the new social edifice, we are unable to foresee them, precisely because the new social edifice will be, and is, a _natural_ and _spontaneous_ product of human evolution, a product which is already in process of formation, and the general outlines of which are already visible, and not an artificial construction of the imagination of some utopian or idealist. The situation is the same in the social sciences and the natural sciences. In embryology the celebrated law of Haeckel tells us that the development of the _individual_ embryo reproduces in miniature the various forms of development of the animal _species_ which have preceded it in the zoological series. But the biologist, by studying a human embryo of a few days' or a few weeks' growth, can not tell whether it will be male or female, and still less whether it will be a strong or a weak individual, phlegmatic or nervous, intelligent or not. He can only tell the general lines of the future evolution of that individual, and must leave it to time to show the exact character of all the particular details of its personality, which will be developed naturally and spontaneously, in conformity with the hereditary organic conditions and the conditions of the environment in which it will live. This is what can be and what must be the reply of every socialist. This is the position taken by Bebel in the German _Reichstag_[63] in his reply to those who wish to know at the present time what all the details of the future State will be, and who skilfully profiting by the ingenuity of the socialist romancers, criticize their artificial fantasies which are true in their general outlines, but arbitrary in their details.