So far, then, we have thus traced the evolutionary process of group formation--and we seem to find confirmed that affirmation as to the primordial order of succession in the genetic growth of custom which I ventured to submit in my first pages, viz. primo: the existence of an early idea of concupiscent lust, distinctive of the male head of a group, which led to his pretensions in marital right over all its component females in necessary incestuous union; secundo, the evolution of the primal law (with what little of originally ethical intention is now immaterial), in protection of such right when threatened by intruders; tertio, its acceptance by the latter, and, as an inevitable sequel, their indispensable capture of outside females as sole possible mates.[6] But then this question of the absolute necessity of the rape of strange females as mates by the young males of a group, opens up to view another remarkable coincidence of effect in custom, still enduring to our day. As such it may furnish a clue to a feature in savage habits, to which we have already alluded as the cause of more discussion, concerning its origin, than any other. For habitual hostile capture of females outside a group by its male members, with a coincidental bar to sexual union with its component females, seems simply a definition of that habit among many actual peoples which has been called Exogamy by Mr. J. F. McLennan. Hence comes the evident corollary to the argument that the primal law and exogamy stand to each other in the mutual relation of cause and effect. We stated that if this was in reality the case, and if here we have the origin of marriage outside the group, then the novelty of the view, and the fact that it finds itself in opposition to other theories on the matter, weighty from the eminence of their propounders, would still require the production of a clear series of proofs in its favour if it was to be accepted. Such proofs, however, we predicted, would with research be found abundantly. We hope that already in our thesis, as far as it has gone, we may be considered to have advanced some such testimony in the seemingly necessary identity of custom, in form at least, in a hypothetic ancient and an actual modern era. There is surely here more than mere fortuitous coincidence in social evolution. It seems, indeed, a legitimate inference that the divers habits of avoidance which we have cited, intelligible only by their congruency with such phases of genetic growth of custom as we have surmised, whilst presenting features utterly anomalous as latter-day creations, are in reality of the archaic origin we would assign to them. Their extraordinary vitality, which becomes almost bewildering to contemplate, may be explained by the fact that, as the first steps in progress, they would be necessarily woven into the whole social fabric.