Up to the present, although the entire male element in a group was divided into two classes, by generations whose interests had little in common, between them no antagonism had arisen which could not be appeased by the evolution of such a law in remedy as we have noted. The case would now be altered; an irreconcilable breach was about to divide them. It will be seen that the advent of the outsider had been a real portent. Where, for instance, and under the circumstances we have portrayed, he had become a more accustomed figure as an immigrant, he would form a valuable connecting link between groups. Each would certainly possess some females seized from the other by more or less forcible capture, but each now possessed a certain proportion of these males, brothers of those females, whose intrusion had been peaceably accepted. With less strained relations and greater intercourse, capture would become a little more rare, and a friendly interchange of women more common. There would be then discovered by the brother a hitherto undreamt-of virtue in the young female, his sister; in fact, her value as a negotiable article would appear. As brothers and sisters, and thus barred in union by the primal law, their relative interest in each other had been of the feeblest in the past. The ultimate destiny of the sister might be a matter of the most perfect indifference to the brother. With the new order of things she had suddenly become more precious. As an object of barter for the sister of another man, she would show herself to be invaluable. In view of the difficulty and danger attending hostile capture, the temptation to such easy procuration of mates as sister-barter offered would be irresistible. Coming at first into practice when only the death of the father had left his widowed daughter free, its advantages to the sons would impose a gradual encroachment on the rights of possession by the living parent. In prejudice to incest were now opposed the two most powerful passions in human nature, sexual desire, and a love of material gain, and the successful barter of a sister for another man’s sister satisfied both. For attempts at capture might be unsuccessful, and purchase might be more or less unsatisfactory. And these passions would be aroused in bosoms able to make their power felt. The sons, as also resident males, would be among the law-makers. However powerful the father in past authority and tradition, in the end the force of numbers would tell. However numerous the group of fathers, they would always be outnumbered by the group of brother sons, and victory would thus ultimately incline to these.[5] However long and doubtful the struggle, as the latter possessed the longer lease of life, the _quantum_ of the exchange value of a sister would always finally be made to show itself, and the determination to profit thereby would be more strongly impressed on each generation.