Board Thread:Naruto Discussions/@comment-3232093-20140617193601/@comment-4271790-20140821165818

Elveonora wrote: Also it was a hypothesis not a theory. Essentially: "hey, what if Sharingan + face of a certain man make up Rinnegan?" There's no actual evolution going on. One-eyed Rinnegan came first (Kaguya), then Rinnegan and Sharingan as separate doujutsu in one person (Hagoromo) and eventually Sharingan in one clan (Uchiha) and Rinnegan stuff in another (Senju) so it's really not an evolution to get Rinnegan from a Sharingan, it's going backwards. Basically the Rinnegan-Sharigan thing downgraded in every generation. Okay, to sum up Orochimaru and Kabuto's theory and the words on the stone monument, and I'm paraphrasing here: There is Kaguya's Third-eyed, nine tomoe, Sharingan-powered, red Rinnegan; Hagoromo's dual, light purple, tomoe-less Rinnegan (which appears different in Sasuke's optic nerves, as a left-eyed, six tomoe, light purple Rinnegan); and the dual Sharingan. The Sharingan can evolve into the light purple Rinnegan, in order for that to happen, a Sharingan user must have Indra and Asura's chakras to bring forth Hagoromo's chakra (or just have Hagoromo's chakra and the Sharingan in Sasuke's case) and awaken a light purple Rinnegan. The light purple Rinnegan can bring forth a red Rinnegan on the forehead, in order for that to happen, a light purple Rinnegan user must also be the TT jinchuuriki and approach the moon (where she was sealed) to awaken an on-the-forehead, red Rinnegan. So @Elveo was right again, the eyes downgraded, and to upgrade the eyes, extra chakra is required (whether it be Hagoromo's chakra or the TT chakra with a short distance from the moon). Long story short, you need the Sharingan and Hagoromo's chakra to get his eyes, and then you need Hagoromo's eyes, Kaguya's chakra and proximity to the moon to get her eye.