Like the savages of to-day, our distant ancestors were very little removed from simple animal existence. A knowledge of their physiology is nevertheless necessary to enable us to understand our own; for, however cultivated the civilised man may be, he derives from the humble progenitors of his race a number of instincts which are energetic in proportion as they are of a low order. More or less deadened, these gross tendencies are latent in the most highly developed individuals; and when they sometimes break out suddenly in the actions of a man’s life, or in the morals or literature of a people, they recall to us our very humble origin, and even show a certain mental and moral retrogression. Now it is to this primitive man, still in such a rudimentary state, that we must go back for enlightenment on the genesis of all our social institutions. We must take him at the most distant dawn of humanity, follow him step by step in his slow metamorphoses, without either disparaging or poetising him; we must watch him rising and becoming more refined through accumulated centuries, till he loses by degrees his animal instincts, and at length acquires aptitudes, inclinations, and faculties that are truly human. Nothing is better adapted to exemplify the evolution which binds our present to our past and to our future than the sociological history of marriage and of the family. After having spoken of the aim of this book, it remains for me to justify its method. This differs considerably from what the mass of the public like far too well. But a scientific treatise must not take purely literary works for its models; and I can say to my readers, with much more reason than old Rabelais, that if they wish to taste the marrow, they must take the trouble to break the bone. My first and chief consideration is to assist in the foundation of a new science--ethnographical sociology. Elegant and vain dissertations, or vague generalities, have no place here. It is by giving way to these, and in attempting to reap the harvest before sowing the seed, that many authors have lost themselves in a pseudo-sociology, having no foundation, and consequently no value. Social science, if it is to be seriously constituted, must submit with docility to the method of natural science. The first task, and the one which especially falls to the lot of the sociologists of the present day, is to collect the facts which will form materials for the future edifice. To their successors will fall the pleasure of completing and adorning it. The present work is, therefore, above all, a collection of facts which, even if taken alone, are curious and suggestive. These facts have been patiently gleaned from the writings of ethnographers, travellers, legists, and historians. I have classed them as well as I could, and naturally they have inspired me here and there with glimpses of possible inductions, and with some slight attempts at generalisation.