Board Thread:Naruto Discussions/@comment-24837927-20140421121126/@comment-1512913-20140422184139

According to current majority's reasoning, Kaguya's Sharingan/Rinnegan whatever was a Tailed Beast Skill while only Hagoromo's Kekkei Genkai since he was presumably born with it. This reasoning obviously has to change, because it's wrong. All advanced natures and stuff should be considered a Kekkei Genkai, even if used by a Tailed Beast. They didn't have to be born through sex nor do they have to pass on the traits through reproduction, chakra alone can do so.

First humans to use chakra after the Trinity didn't presumably even have chakra pathway system originally. They got it from Hagoromo's chakra transfer and only their children were born with it. You could say it evolved humans. Chakra obviously has effect on physiology, hence Naruto gets fox traits once too much of Kurama's chakra takes over. Even more drastic exposure to chakra highly likely affects genetics itself, hence Kaguya.