Board Thread:Naruto Discussions/@comment-945885-20140709082448/@comment-24593592-20140719174250

Skitts wrote: I actually think it's a little silly to assume (at least until it's stated) that all KKG originate with Kaguya. That seems to take biology backwards, that is, these mutations are passed on, but her descendants never have more than one of them.

Furthermore, we know that Hagoromo gave other people, unrelated to him, the ability to create chakra, so any number of KKG could have developed from those individuals and/or their descendants.

Were they ever established as fact to be mutations? That was only stated for the Rinnegan by Kakashi which he was wrong about.