Now all these factors--and others too perhaps--may very well have had their influence in bringing about the practice of exogamy: in particular, it would seem that the difficulty of supporting a large family living together under really primitive conditions would be very likely to have had the effect of driving the younger members of the family away from the immediate circle of their parents. Nevertheless there appears to be a pretty general agreement that none of these theories affords a complete and sufficient account of the origin of exogamy. The conditions postulated by McLennan's theory (shortage of women and frequent wars between neighbouring groups) are by no means universally found among primitive peoples, and even if there exists the required preponderance of men over women, it is by no means obvious why the men should refuse to avail themselves of such fellow-tribeswomen as they could find. On Spencer's view, it is difficult or impossible to account for the existence of exogamy among all the tribes of a given area, since in constant warfare there must be some which are vanquished, and among these endogamy rather than exogamy should be the rule. Lord Avebury's theory rests on the assumption that communal marriage was the original condition of mankind--an assumption that is now abandoned by many of the best authorities. Kohler's view can scarcely explain how the objection to sexual unions within the tribe should have come to apply not only to marriage but (equally strongly) to less regular or purely temporary connections. Andrew Lang's theory similarly fails to explain why the rule of exogamy is made to apply to the elder members of the family with the same force as to the younger[260]. [Sidenote: The psychological nature of the incest prohibition shows the insufficiency of these influences]