In encyclopedical and philosophical works we meet with several different definitions of the word marriage. Most of these definitions are, however, of a merely juridical or ethical nature, comprehending either what is required to make the union legal,[93] or what, in the eye of an idealist, the union ought to be.[94] But it is scarcely necessary to say how far I am here from using the word in either of these senses. It is the natural history of human marriage that is the object of this treatise; and, from a scientific point of view, I think there is but one definition which may claim to be generally admitted, that, namely, according to which marriage is nothing else than a more or less durable connection between male and female, lasting beyond the mere act of propagation till after the birth of the offspring. This definition is wide enough to include all others hitherto given, and narrow enough to exclude those wholly loose connections which by usage are never honoured with the name of marriage. It implies not only sexual relations, but also living together, as is set forth in the proverb of the Middle Ages, “Boire, manger, coucher ensemble est mariage, ce me semble.”[95] And, though, rather vague, which is a matter of course, it has the advantage of comprehending in one notion phenomena essentially similar and having a common origin. Thus, as appears from the preceding investigation, the first traces of marriage are found among the Chelonia. With the Birds it is an almost universal institution, whilst, among the Mammals, it is restricted to certain species only. We observed, however, that it occurs, as a rule, among the monkeys, especially the anthropomorphous apes as well as in the races of men. Is it probable, then, that marriage was transmitted to man from some ape-like ancestor, and that there never was a time when it did not occur in the human race? These questions cannot be answered before we have found out the cause to which it owes its origin.