Board Thread:Naruto Discussions/@comment-3232093-20140617193601/@comment-1512913-20140821113118

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.