Evolution would select out useless body parts unless a sudden change in environment/diet is observed which makes the body part useless/redundant. Such as the rise of human civilisation.
But only a god/gods would create an organ that is useless and has been useless for many many generations of our ancestors. This discounts a sudden change in environment as an explanation, since it should only affect the first few generations.
I have a theory that it's impossible to prove anything, but I can't prove it.