Board Thread:Naruto Discussions/@comment-4080775-20180410150203/@comment-1512913-20180411114858

That's the most common misconception that the Rinnegan can come from the Sharingan. The reason for this is that most Rinnegan users had started with the Sharingan before they awakened the Rinnegan, thus creating a false impression that their Sharingan evolved into the Rinnegan or that the Sharingan is a necessary requirement.

The Sharingan and Rinnegan are as different doujutsu as the Sharingan/Byakugan or Byakugan/Rinnegan are. The only thing the Sharingan and Rinnegan have in common is that they are sibling doujutsu to each other and Rinne Sharingan is their parent.

If they were evolutions of each other, they would be no sibling doujutsu, but parent-child to each other.