The innumerable dissertations on the history of marriage and of the family which appeared previous to the rise of scientific method, have necessarily been devoid of accuracy and especially of breadth of thought. A thick veil concealed the real origin of these institutions; religious legends, that had become venerable on account of their antiquity, paralysed scientific investigation. To submit our social institutions to the great law of evolution, by means of disagreeable researches, was not to be tolerated by public opinion. In fact, if marriage and the family have been constantly modified in the past, we cannot maintain that these institutions will remain for ever crystallised in their present state. Until this revolutionary idea had taken root and become sufficiently acclimatised in public opinion, all so-called social studies were scarcely more than empty lucubrations. From time to time, no doubt, a few bold innovators, braving scoffs or even martyrdom, have dared to construct theories of new societies; but, being insufficiently informed, they could only create Utopias contemned by the mass of the public. Scientific sociology builds its edifice stone by stone; its duty is to bind the present to the most distant past; its honour will lie in furnishing a solid basis of operation to the innovators of the future; but this new branch of human knowledge can only grow by submitting to the method of the natural sciences. Before everything else, it is important to classify the facts that have been observed. This course is imperative. It is dry, and lends itself with difficulty to oratorical effusions, but no other path can lead to the truth. My constant anxiety has been to be faithful to it, and as an anthropologist I have especially borrowed my materials from ethnography. Step by step, and following as much as possible the hierarchic order of human races and of civilisations, I have described the modes of marriage and of the family adopted by the numerous varieties of the human type; I have endeavoured to note the phases of their evolution, and to show how superior forms have evolved from inferior ones. Now that I am at the end of my inquiry, it will be well to sum up clearly its result. The prime cause of marriage and the family is purely biological; it is the powerful instinct of reproduction, the condition of the duration of species, and the origin of which is necessarily contemporaneous with that of primal organisms, of protoplasmic monads, multiplying themselves by unconscious scissiparity. By a slow specialisation of organs and functions, in obedience to the laws of evolutionary selection, various animal types have been created; and when they have been provided with separate sexes and conscious nervous centres, procreation has become a tyrannic need, driving males and females to unite in order to fulfil the important function of reproduction.