It is unnecessary to say much about this hypothesis, as it stands or falls with Sir J. Lubbock’s theory of “communal marriage.” Why should women taken in war have been the men’s personal property, if the women of the tribe were not so? As Mr. McLennan justly remarks, war-captives are usually obtained by group-acts, or quasi group-acts; hence capture would be recognized as a regular mode of adding women to the group, subject to the customary rights of its male members; and every man in the group would claim the communal right to women taken by others.1887

Again, Professor Kohler has expressed his belief in the explanation that exogamy was an early method of political self-preservation.1888 That intermarriage is valuable from a political point of view, and has often taken place in order to increase intertribal or international friendship, is beyond doubt.1889 But it is another question whether the strictly prohibitive exogamous rules, the infringement of which is considered a most heinous crime, can be accounted for in this way. It is worth noticing that not only marriage, but also less regular connections between members of the same exogamous group are held in horror. The Australians, for instance, consider cohabitation between individuals belonging to clans that cannot intermarry not less criminal than marriage, often punishing such unions with death.1890 Among the Melanesians, says Dr. Codrington, “intercourse within the limit which restrains from marriage, where two members of the same division are concerned, is a crime, is incest.”1891 Holm makes a similar observation on the prohibited degrees among the Eastern Greenlanders.1892 Speaking of the Samoans, Mr. Prichard remarks, “Of all their customs, the most strictly observed, perhaps, was that which forbade the remotest reference to anything, even by way of a joke, that conveyed the slightest indelicacy in thought or word or gesture, when brothers and sisters were together. In presence of his sister, the wildest rake was always modest and moral. In presence of her brother, the most accommodating coquette was always chaste and reserved. This custom remains intact to the present day.”1893 Dr. Tylor remarks that anthropologists have long had before them the problem of determining how far clan-exogamy may have been the origin of the prohibited degrees in matrimony.1894 But we have seen that it is practically impossible to trace any distinct limit between these two sets of rules; hence they seem to be fundamentally identical—a conclusion in which most anthropologists agree. And the prohibitions of close intermarriage certainly cannot be explained as a “method of political self-preservation.”

Other writers—and among them Mr. Morgan—have suggested that prohibitions of the marriage of near kin have arisen from observation of the injurious results of such unions.1895 But most investigators who have considered the subject believe that this knowledge could be gained only by lengthened observation, and, to quote Dr. Peschel, is “unattainable by unsettled and childishly heedless races,” among whom, nevertheless, a horror of incest is developed most strongly.1896 Sir Henry Maine, on the other hand, thinks that the men who discovered the use of fire and selected the wild forms of certain animals for domestication and of vegetables for cultivation, might also have been able to find out that children of unsound constitution were born of nearly related parents.1897 In the next chapter, I shall have occasion to mention some instances which possibly may point in this direction, but in no case does such knowledge appear to be generally diffused among backward races. Mr. Curr has been unable to discover on what ground consanguineous marriages are held to be objectionable by the Australians, their replies to questions on this head invariably being, “Our tribe always did as we do in this matter.” Yet they are well aware, he says, that the aim of the exogamous restrictions is to prevent the union of nearly related individuals.1898 Dr. Sims writes that no other reason for the avoidance of marriage between near relations has been stated to him by the indigenous Bateke than that of “shame.” Mr. Bridges informs me that the Yahgans point simply to the fact of relationship as the reason; and, when Azara asked the Charruas why a brother and sister never intermarried, they replied that they did not know why.1899 It is conceivable that the experience of the injurious results of such marriages, once acquired, might afterwards have fallen into oblivion, although the prohibition continued to exist. But Azara expressly states that the Charruas have no law forbidding incestuous alliances, yet he has never seen nor heard of any among them.

Whatever observations may have been made, the prohibition of incest is in no case founded on experience. Had the savage man discerned that children born of marriage between closely related persons are not so sound and vigorous as others, he would scarcely have allowed this knowledge to check his passions. Considering how seldom a civilised man who has any disease, or tendency to disease, which is likely to be transmitted to his descendants, hesitates to marry an equally unhealthy woman, it would surely be unreasonable to suppose that savages have greater forethought and self-command.1900 But even if we admit that man originally avoided marriage with near kin from sagacious calculation, and that he did this during so long a period that usage grew into law, we do not advance a step further. All the writers whose hypotheses have been considered in this chapter, assume that men avoid incestuous marriages only because they are taught to do so. “It is probable,” says Mr. Huth, “that, if brothers and sisters were allowed to marry, they would do so while yet too young.”1901 But though law and custom may prevent passion from passing into action, they cannot wholly destroy its inward power. Law may forbid a son to marry his mother, a brother his sister, but it could not prevent him from desiring such a union if the desire were natural. Where does that appetite exist? The home is kept pure from incestuous defilement neither by laws, nor by customs, nor by education, but by an instinct which under normal circumstances makes sexual love between the nearest kin a psychical impossibility. An unwritten law, says Plato, defends “as sufficiently as possible,” parents from incestuous intercourse with their children, brothers from intercourse with their sisters: “ἀλλ’ οὐδ’ ἐπιθυμία ταύτης τῆς συνουσίας τὸ παρ ‘παν εἰσέρχεται τοὺς πολλοὺς”—“nor does even the desire for this intercourse come at all upon the masses.”1902