But it is in special relation to the further movement in advance implied in the friendly aggregation of groups into a tribe that the effects of paternal incest would be most fatally felt. For while it reigned as a custom and a father usurped sole marital right over the whole feminine element, the immigration into the group of outside suitors for their hands would be impossible, their possession by the latter would be only possible after capture, which, being hostile, would tend to keep asunder the different groups. And yet in the next and higher stage of social evolution, as presented in the amalgamation of groups into a tribe, the acceptation of these outside mates in peaceful connubium is precisely the most characteristic feature. In later days they will be found as the male members of a certain ‘class’ in one ‘phratry,’ and, _de facto_, eligible in group marriage with all and certain females of the corresponding category as regards birth in another phratry, within an all-embracing tribe. As indeed with actual Australians, where, by right of birth alone each ‘class’ contains the natural born husbands of the wives of another ‘class.’ Such connubium is evidently impossible while incest flourished as a custom, it could only arise after its decay.[2] It thus becomes necessary to study by what possible conjunction of affairs so desirable a result was arrived at. We will find that, however fortuitous the event of the primary inclusion of an outside possible suitor within a group, however timid and hesitating his entry, his presence there would be the signal of the beginning of the end. Now it is evidently hopeless to look for any voluntary acceptance of his claims by the living father, to whom the temptation to so easy a procuring of an inmate of his harem as his own daughter would be irresistible. There would be also on his side all habit and tradition, and with no direct group interest in opposition, the brothers being unconcerned. The initiative in change must then arise irrespective of him, and without the obstacle of his presence. This could only be possible thus after his death. Now it is important to observe that precisely the embarrassment we have seen arise after this event must be a means to the end of the conjunction we seek. We have noted the danger of the situation under such circumstances; ineligible in union by the primal law with the remaining male element, which is composed of their own brothers, temptations to its infraction would be as frequent as fatal, on the part of the early widowed sisters. On the other hand, the anomaly of a celibate existence in the animal stage would tend to the secession of widows, so to speak, to hostile hordes, or to constant attempts at hostile capture by the outside suitor. But with the friendly entry of the latter and his acceptance as a group member, all these disturbing influences would at once cease; further, the value of an extra unit of strength in his presence would soon make itself felt.