Among the theories which seek to explain exogamy independently of totemism only a few need be mentioned in so far as they illustrate different attitudes of the authors towards the problem of incest. MacLennan[176] had ingeniously guessed that exogamy resulted from the remnants of customs pointing to earlier forms of female rape. He assumed that it was the general custom in ancient times to procure women from strange tribes so that marriage with a woman from the same tribe gradually became “improper because it was unusual”. He sought the motive for the exogamous habit in the scarcity of women among these tribes, which had resulted from the custom of killing most female children at birth. We are not concerned here with investigation whether actual conditions corroborate MacLennan’s assumptions. We are more interested in the argument that these premises still leave it unexplained why the male members of the tribe should have made these few women of their blood inaccessible to themselves, as well as in the manner in which the incest problem is here entirely neglected[177]. Other writers have on the contrary assumed, and evidently with more right, that exogamy is to be interpreted as an institution for the prevention of incest[178]. If we survey the gradually increasing complication of Australian marriage restrictions we can hardly help agreeing with the opinion of Morgan Frazer, Hewitt and Baldwin Spencer[179], that these institutions bear the stamp of ‘deliberate design’, as Frazer puts it, and that they were meant to do what they have actually accomplished. “In no other way does it seem possible to explain in all its details a system at once so complex and so regular”[180]. It is of interest to point out that the first restrictions which the introduction of marriage classes brought about affected the sexual freedom of the younger generation, in other words, incest between brothers and sisters and between sons and mothers, while incest between father and daughter was only abrogated by more sweeping measures. However, to trace back exogamous sexual restrictions to legal intentions does not add anything to the understanding of the motive which created these institutions. From what source, in the final analysis, springs the dread of incest which must be recognized as the root of exogamy? It evidently does not suffice to appeal to an instinctive aversion against sexual intercourse with blood relatives, that is to say, to the fact of incest dread, in order to explain the dread of incest, if social experience shows that, in spite of this instinct, incest is not a rare occurrence even in our society, and if the experience of history can acquaint us with cases in which incestuous marriage of privileged persons was made the rule.