I haven't the foggiest.....and my money's on that we probably will never come to a fullfilling answer. I think that's how it was meant to be,its what keeps our soul alive......the mystery of life
As Einstein once said
"The human mind is not capable of grasping the Universe. We are like a little child entering a huge library. The walls are covered to the ceilings with books in many different tongues. The child knows that someone must have written these books. It does not know who or how. It does not understand the languages in which they are written. But the child notes a definite plan in the arrangement of the books---a mysterious order which it does not comprehend, but only dimly suspects."
So the important thing is to never stop wondering.Never lose holy curiosity of the mysteries of eternity, of life, of the marvelous structure of reality.
I mean why have a mind if not to question why???