If the Sage of 6 paths is merely a combination of both the Uchiha and Senju bloodlines, then how would the Uzumaki line fit into that? As we have seen, the Uzumaki clan possessed both long life and an affinity for controling the bijuu. Both of those traits seem tied into the Rikudou bloodline. Yet, if the Senju are the only decendents of the younger brother and the Uchiha are the only decendants of the elder brother, why do the Uzumaki possess those traits? Nagato being an Uzumaki is significant, but to what degree, why was he chosen and or how did he obtain the Rinnegan? Even if Madara did awaken it himself and give it to Nagato, he must have had a good reason for choosing Nagato, an Uzumaki specifically.