Hey I came up with a weird idea. We know for a fact that the Schibukai 'Bartholomew Kuma' is often seen with a book in his hand with the title "Bible" on it's cover.
We have a book with that title as well in this world. Kuma always carries it around as if he worships the book, also, the picture on the book suggests a holy person. So it's probable that the book is also holy in the One Piece world.
What if kuma's bible is the Christian bible? That would mean that Jezus also existed in the One Piece world. And Jezus is known for his 'miracles' or 'powers' such as the ability to walk on water or to resurect from the death. And what do you conclude when someone in the One Piece world does something extraordinary? Exactly, say: "He must have eaten a devilsfruit!"
What are your ideas on this?