Board Thread:Theories and Speculation/@comment-1512913-20160709202754/@comment-1872728-20160712155147

Elveonora wrote: Meaning that Six Paths Senjutsu isn't an original, innate trait of Hagoromo's chakra, but something he developed later in his life. I think I get what you mean now, but I still think that it's genetically related somehow.

The Chakra Fruit bears most of the Physical Energy and Spiritual Energy of the people on Earth. It also bears most of the Natural Energy on Earth, so the Chakra Fruit is basically the Sage Chakra Fruit.

When Kaguya ate the fruit, she changed physically, which gives the impression that her genetics are changed as well, which also means that her chakra is now permanently composed of at least Sage Chakra.

Also, after Hagoromo manifested his Rinnegan, his Sage Mode manifested a Rinnegan-like marking on his forehead, which looks as if his Sage Mode is being mutated by his Rinnegan (genetics), so I think that Six Paths Sage Mode is an innate trait, but it's just inactive until the person learns Sage Mode.

This can also be applied to Hashirama, since his forehead also bears an eye-like marking, which could mean that he learned Sage Mode without the help of others (like Hagoromo), then his genetics mutated his Sage Mode, gaining an eye-like marking on his forehead. And since he's a Gen3, his marking looks like a normal eye, with unique markings around the eyes, which contrasts with the Mangekyo Sharingan, a normal eye (not like Rinnegan which covers the whole eyeball) with unique markings on the eyes.

And the reason why Naruto didn't get the marking, is because only Senju Clan has this ability, while the Uzumaki Clan has the Chakra Structure Mode ability, whereas the Uchiha Clan has both.