A superficial glance at the history of evolution suffices to teach us that innumerable complicated functions, whose sexual character must be denied, are originally nothing but derivations from the instinct of propagation. As is well known, there has been an important displacement in the fundamentals of propagation during the ascent through the animal scale. The offspring has been reduced in number, and the primitive uncertainty of impregnation has been replaced by a quite assured impregnation, and a more effective protection of offspring. The energy required for the production of eggs and sperma has been transferred into the creation of mechanisms of attraction, and mechanisms for the protection of offspring. Here we find the first instincts of art in animals, used for the instinct of propagation, and limited to the rutting season. The original sexual character of these biological institutions became lost with their organic fixation, and their functional independence. None the less, there can be no doubt as to their sexual origin, as, for instance, there is no doubt about the original relation between sexuality and music, but it would be a generalization as futile, as unesthetic, to include music under the category of sexuality. Such a terminology would lead to the consideration of the Cathedral of Cologne under mineralogy, because it has been built with stones. Those quite ignorant of the problems of evolution are much astonished to find how few things there are in human life which cannot finally be reduced to the instinct of propagation. It embraces nearly everything, I think, that is dear and precious to us. We have hitherto spoken of the libido as of the instinct of reproduction, or the instinct of the preservation of the species, and limited our conception to that libido which is opposed to hunger, just as the instinct of the preservation of the species is opposed to that of self-preservation. Of course in nature this artificial distinction does not exist. Here we find only a continuous instinct of life, a will to live, which tries to obtain the propagation of the whole race by the preservation of the individual. To this extent this conception coincides with that of Schopenhauer’s “will,” as objectively we can only conceive a movement as a manifestation of an internal desire. As we have already boldly concluded that the libido, which originally subserved the creation of eggs and seed, is now firmly organized in the function of nest-building, and can no longer be employed otherwise, we are similarly obliged to include in this conception every desire, hunger no less. We have no warrant whatever for differentiating essentially the desire to build nests from the desire to eat.