For all these reasons, and because of the improbability of the physiological discovery, and of the moral 'reform' which enforced it; and again, because the law is not of the sort which people acquainted with near degrees of kinship would make; and once more because the law fails to effect its presumed purpose, while it does attain ends at which it does not aim--we cannot accept Mr. Morgan's suggestion as to the origin of exogamy. Mr. M'Lennan did not live to publish a subtle theory of the origin of exogamy, which he had elaborated. In _Studies in Ancient History_ he hazarded a conjecture based on female infanticide:--
We believe the restrictions on marriage to be connected with the practice in early times of female infanticide, which rendering women scarce, led at once to polyandry within the tribe, and the capturing of women from without.... Hence the cruel custom which, leaving the primitive human hordes with very few young women of their own, occasionally with none, and in any case seriously disturbing the balance of the sexes within the hordes, forces them to prey upon one another for wives. Usage, induced by necessity, would in time establish a prejudice among the tribes observing it, a prejudice strong as a principle of religion--as every prejudice relating to marriage is apt to be--against marrying women of their own stock.
Mr. M'Lennan describes his own hypothesis as 'a suggestion thrown out at what it was worth.'[217] In his later years, as we have said, he developed a very subtle and ingenious theory of the origin of exogamy, still connecting it with scarcity of women, but making use of various supposed stages and processes in the development of the law. That speculation remains unpublished. To myself, the suggestion given in _Studies in Ancient History_ seems inadequate. I find it difficult to conceive that the frequent habit of stealing women should indispose men to marry the native women they had at hand. That this indisposition should grow into a positive law, and the infringement of the law be regarded as a capital offence, seems more inconceivable. My own impression is, that exogamy may be connected with some early superstition or idea of which we have lost the touch, and which we can no longer explain.[218] Possibly it may be only one form of the Totem taboo. You may not marry a woman of your totem, as you may not eat an animal of the species.