In this respect man is strictly assimilable to the other animals, and with him as with them all the intoxication of love has for its initial principle the elective affinity of two generating cellules of different sex. So far, this is mere biology, but it results, among superior animals, in sociological phenomena, in pairings which endure after the satisfaction of procreative needs, and produce in outline some forms of human marriage, or rather, of sexual union in humanity--namely, promiscuity, polygamy, and even monogamy. Our most primitive ancestors, our precursors, half men and half apes, have certainly had extremely gross customs, which are still in great measure preserved among the least developed races. The study, however, of contemporary savage societies proves to us that absolutely unbridled promiscuity, without rule or restraint, is very rare even in inferior humanity. In exceptional cases, individuals of both sexes may have abandoned themselves, of common accord, to promiscuity, as did the Polynesian _areoïs_; but these instances relate to acts of debauchery, and not to a regulated social condition compatible with the maintenance of an ethnic group. The conjugal form nearest to promiscuity is the collective marriage of clan to clan--as, for example, that of the Kamilaroi, amongst whom all the men of one clan are reputed brothers to each other, and at the same time husbands of all the women of a neighbouring clan, reputed also sisters to each other. Other varieties of sexual association are more common, and may be arranged under the general heads of promiscuity, polygamy, polyandry, and monogamy. We hear also of temporary unions, marriages for a term, and partial marriages concluded at a debated price for certain days of the week only, etc. Every possible experiment, compatible with the duration of savage or barbarous societies, has been tried, or is still practised, amongst various races, without the least thought of the moral ideas generally prevailing in Europe, and which our metaphysicians proclaim as innate and necessary. Having elsewhere demonstrated at length the relativity of morality, I will not go over the ground again, but will quote on this point some lines of Montaigne:--“The laws of conscience, which we pretend to be derived from nature, proceed from custom; every one having an inward veneration for the opinions and manners approved and received amongst his own people, cannot without very great reluctancy depart from them, nor apply himself to them without applause.... The common fancies that we find in repute everywhere about us, and infused into our mind with the seed of our fathers, appear to be most universal and genuine. From whence it comes to pass, that whatever is off the hinges of custom is believed to be also off the hinges of reason.”[1108] The partial marriages of the Hassinyeh Arabs are surely off the hinges of our custom; and it is the same with polyandry, which borders on these