These really are questions for people who know more about anthropology than I do, which wouldn't take much.
Have records been maintained regarding surviving 'Stone Age' tribes' religions? Is there a trend towards pantheism, polytheism, or some other form of theism? Is there any record of a tribe without any divine or divine-like belief system?
I started thinking about it when I read about the 'discovery' of another amazon tribe a few months ago, but I really don't know how to go about researching such a broad question so far from my own education.