I'm going to assume that by 'God' you mean the Christian god. What demonstratable evidence can you present that the Christian god is the origin of the universe as we know it?
As for the origin of religion, our current historical and archealogical evidence shows that the Judeo-Christian religion was formed from a blend of the various myths and stories of those tribes, and underwent many significant changes over time to becoming what it is today.
Also, I'd like to know why you view the story of Adam as fact? There are stories from other religions that have survived to the present day. Can you please show me the evidence that Adam is real, but Hercules isn't?
I can not prove that the Christian god does not exist, as I can not prove that Allah does not exist. I can not prove that Thor, Odin, or Loki do not exist. I can not prove that Rah, Isis, or Osiris do not exist. I can not prove that Zeus, Poseidon, or Hades do not exist. I can not prove that dragons, or unicorns, or leprechauns do not exist. I can not prove that Galactic Overlord Xenu, of Scientology fame does not exist. It is impossible and unnecessary to prove a negative. If you are the one claiming something or someone exists, whether it be a magical creature, an alien, or a diety, then the burden of proof is upon you.