The Early History of the Family

'We believe the restrictions on marriage to be connected with thepractice in early times of female infanticide, which, rendering womenscarce, led at once to polyandry within the tribe, and the capturingof women from without. . . . Hence the cruel custom which, leavingthe primitive human hordes with very few young women of their own,occasionally with none, and in any case seriously disturbing thebalance of the sexes within the hordes, forces them to prey upon oneanother for wives. Usage, induced by necessity, would in timeestablish a prejudice among the tribes observing it, a prejudicestrong as a principle of religion—as every prejudice relating tomarriage is apt to be—against marrying women of their own stock.'