Neither the conditions of absolute monogamy, nor those of absolute promiscuity seem to be found at present in humanity, nor among animals; but one sees the couple, in several animal and human species, either in state of tendency, or in state of habit. More often, especially among insects, the father, even if he survives it a little while, remains indifferent, to the consequences of the genital act. At other times, the fights between males so reduce their number that a sole male remains the master and servant of a great number of females. So one must distinguish between true, and successive polygamy; between the monogamy of one season, and that of an entire lifetime; and finally one must set apart those animals who make love only once, or during one season which is followed by death. These different varieties and nuances demand methodic classification. It would be a long work, and would perhaps not attain true exactitude, for in animals, as in man, one must count with caprice in sexual matters: when a faithful dove is tired of her lover, she takes flight, and soon forms a new couple with an adulterous male. The couple is natural, but the permanent couple is not. Man has never bent to it, save with difficulty, even though it be one of the principal conditions of his superiority.
The breasts of the male do not seem to prove the primordiality of the couple in mammals. Although there are veridic examples of the male's having given suck, it is difficult to consider the male udder as destined for a real rôle, or for an emergency milking.[2] This replacement has been too rarely observed for one to use it as a basis of argument. Embryology gives a good explanation of the existence of this useless organ. An useless instrument is, moreover, quite as frequent in nature as the absence of a useful instrument. Perfect concordance of organ and act is rare. In the case of insects who live but for one love-season, sometimes for two real seasons if they can benumb themselves for the winter, polygamy is nearly always the consequence of the rarity of males, or the superabundance of females. Space is too vast, their food too abundant for there to be truly deadly combats between males. Moreover, their love accomplished, the minuscule folk ask only to die, the couple is formed only for the actual time of fecundation, the two animals at once resume their liberty, that is for the female to deliver her eggs, and for the male to languish, and sometimes to cast a final song to the winds. There are exceptions to this rule, but if one looks upon the exceptions with the same gaze as on the rule, one would see in nature only what one sees on the surface of a river, vague movements and passing shadows. To conceive some reality, one must conceive a rule, first, as an instrument of vision and of measure. With most insects the male does nothing but live; he deposits his seed in the female receptacle, flies on, vanishes. He does not share any of the labours preparatory to laying. Alone the female sphex engages in her terrible and clever strife with the cricket, whom she paralyzes with three stabs of her dagger in his three moto-nervous centres; alone she hollows the oblique burrow at the bottom of which live her larvæ; alone she adorns it, fills it with provisions, closes it. Alone the female cerceris heaps up in the deep gallery the stunned weevils and burn-cows, fruit of her excavations, larder for her progeny. Alone the she-osmie, she-wasp, she-philanthe--one would have to cite nearly all the hymenoptera. One understands better, when the insect deposits her eggs by chance, without prefatory manœuvres, or by special instruments, that the male co-operation is lacking; only the female cicada can sink her clever burrow in the olive bark.