Lets be clear the Sage of th 6 paths was born with the Rinnegan but here is the kicker .....
According to Kuurama(9tails) the Jyuubi created humans thus the is source of the Rinnegan & all other blood limits is the Jyuubi itself. Essentially a human born with the Rinnegan is a human incarnate of the Jyuubi. I mentioned this in my thread a few months ago.
I thought the fox went as far as saying the juubi made the land and gave it chakras, i don't recall humans being an express article of the conversation, i also have a bad memory. Either way, it doesn't lock the juubi as the only source of powers and such available to humans. Dead demon seal is hint if that and the juubi isn't the only figure of the divine order or interpretation of Pantheon.
_____ Obito is Tobirama's great grandson. The proof is in the pudding.