Board Thread:Naruto Discussions/@comment-29393962-20161111215453/@comment-6769189-20170116083111

Rinnegan seems to have a few pre-reqs to activate.

Transmigrant: Indra specifically, Theoretically any descendant could work because chakra signatures are passed down to offsprig, but transmigrants will have the highest concentration of Indra chakra, making them the optimal candidates.

Sharingan: Even if they are different eyes, the Naruto history shows they are very intertwined. The only time we the Rinnegan activate is through the Sharingan. So there is a possibility that the Rinnegan is akin to a recessive trait, only brought about through the Sharingan+6 Paths/Hagoromo/Ashura chakra.