Man has thus gone through the same transition as certain domestic animals. The he-goat[188] and the ass in southern countries,[189] for instance, rut throughout the whole year. The domestic pig pairs generally twice a year, while its wild ancestors had but one rutting season.[190] Dr. Hermann Müller has even observed a canary that laid eggs in autumn and winter.[191] Natural selection cannot, of course, account for such alterations: they fall under the law of variation. It is the limited pairing season that is a product of this powerful process, which acts with full force only under conditions free from civilization and domestication. If the hypothesis set forth in this chapter holds good, it must be admitted that the continued excitement of the sexual instinct could not have played a part in the origin of human marriage—provided that this institution did exist among primitive men. Whether this was the case I shall examine in the following chapters. CHAPTER III THE ANTIQUITY OF HUMAN MARRIAGE If it be admitted that marriage, as a necessary requirement for the existence of certain species, is connected with some peculiarities in their organism, and, more particularly among the highest monkeys, with the paucity of their progeny and their long period of infancy,—it must at the same time be admitted that, among primitive men, from the same causes as among these animals, the sexes in all probability kept together till after the birth of the offspring. Later on, when the human race passed beyond its frugivorous stage and spread over the earth, living chiefly on animal food, the assistance of an adult male became still more necessary for the subsistence of the children. Everywhere the chase devolves on the man, it being a rare exception among savage peoples for a woman to engage in it.[192] Under such conditions a family consisting of mother and young only, would probably, as a rule, have succumbed.