But still other complications will be found to arise as the effect of the original concept of the classificatory system when brought face to face with new and advanced social order, which will have closer relation to our present argument. The distinctive feature in the economy of the primitive group in its relation to all other groups was mutual hostility. The instinctive distrust of strangers would be accentuated by the habitual hostile capture of females, for such groups, except in the case of the incest between father and daughter, were yet purely exogamous. But such mutual hostility implies isolation of each community. Thus all law evolved, as we have said, would be purely with a view to regulation of the internal economy of a single consanguine group alone. Now in such a group, the division into generations of old male, male, and young male implied (although not as yet understood as between generations) the relationship of parents and children. Each generation is either child or parent to the other. As marriage is communal,[10] all the fathers in one generation are fathers to all the children in the next indiscriminately, and conversely these children recognise as fathers all the males of the senior generation. It follows that the relationship of all the members of a generation is purely fraternal, all are brothers and sisters to each other, and in this consanguine family they were really either actually so, or at least half brothers and half sisters. Between these the primal law of celibacy between brother and sister as such embraced the whole generation. Now as long as the family was thus simply constituted, no friction would arise. The brothers, in common, captured and married in common some outside female,[11] and their children constituted solely the next generation. The sisters were either stolen or emigrated to other groups; but we have seen that a moment would come when this process ceased to be universal. The sister came to remain in her own group, and she was joined by some outside suitor; with the advent of their children, who are cousins to the others, would arise dire perplexities, in view of the old law.