Theory: Anime frames of Sasuke. The Original Sharringan, and Implications.
While watching some of the original Naruto anime series, I noticed this. It was very very very brief, all within a matter of a second or two. None the less, they show how the Sharringan forms in the eye.
Notice anything familiar about the shape the Sharringan makes, before the small black pupils form?!?
The Sage of the 6 Paths is the origin of all jutsus, including dojutsu (eye techniques). Most likely, the Hyuuga and Uchiha possesed a genetic structure that enabled them to mimic the Rinnengan. The Sharringan is supposed to be more powerful than the Byakugan.
Sasuke's MS eye, the 3 interlocking circles, is the closest a dojutsu user has ever come to obtaining powers similar to the Rinnengan. I make this assumption because of the structure of the eye, and appearance.
If the Sharringan enable the Uchiha to copy techniques, why not assume that the original Sharringan user obtained the eyes by trying to copy the Rinnengan. Thus, explaining the images I included.
The Sharringan we know and see now, is the progressed and evolved form of the eye in the image I included.
Well... this is my theory... any comments?