lately i have been getting the idea that Superman could be from Earth because when i read stuff like 'Superman: Birthright' and 'Superman Red Son'. I see in 'Red Son' that humans evolve and become like kryptonians and a certain person, Lex Luthor's descendant (Jor-L), sends his son (Kal-L) off to another planet becuase earth is about to suffer the same faith as Krypton.
And on Birthright on the epilogue i see that Jor-El and Lara see a faint video of Superman saying "Father...Mother, i made it". Sothat make me think that they have the technology to do it.
Finally if this is true, then Lex Luthor is Superman's ancestor.