The genesis of this particular avoidance (father-in-law and son-in-law) took place during that stage of the transition era, when, incest still lingering, the immigrant suitor was so far acknowledged that his entry into a group was not always delayed till the death of his proposed father-in-law. As they were thus possible rivals there was a chance of friction, only to be averted by the law in question. Avoidance would arise at the same time between mother-in-law and son-in-law, but this time as a measure of protection for the marital rights of the husband of the former.[9] It could not have arisen in the early Cyclopean era. The son-in-law as such, could evidently not have had existence when the mother’s daughter was the father’s wife, nor, later, when, with the general recognition of the classifactory system, there arose a strict interdiction of sexual union between members of different generations. There would in such circumstances be no further risk of danger from the jealousy of a father as regards his wife, and the husband of his daughter. It had its origin in the fact that when the outside suitor had originally been granted entry, it would only have been after the death of the patriarch sire, and as a mate for his widowed females. But as these would include both mother and daughter, there would thereby be created a precedent, so to speak, which required regulation, when later, with the decay of incest, the living father remained in presence. In fact, avoidance between mothers-in-law and sons-in-law defined fathers-in-law’s rights. We may here again note another step in advance to purely human attributes in the fresh distinction between female and female, which has now again arisen as between a mother and her daughter as regards the immigrant suitor. But whereas with these, as indeed with most of the cases of avoidance we have studied, sexual jealousy has been the primary cause, we may now trace the action of quite another factor, which would certainly tend to a conservation of the habit, and in a manner intensify it. This would be association of idea with hostile capture.