I recall an instance when a person from Canada opined, after hearing some of my beliefs, that I was an animist. I have never researched what exactly that is so really couldn't say.
"Animism, (from Latin anima "soul, life"), refers to the belief that non-human entities are spiritual beings, or at least embody some kind of life-principle. Animism encompasses the beliefs that there is no separation between the spiritual and physical (or material) world, and souls or spirits exist, not only in humans, but also in all other animals, plants, rocks, geographic features such as mountains or rivers, or other entities of the natural environment. Animism may further attribute souls to abstract concepts such as words, true names, or metaphors in mythology."
-- from Wikipedia
My perspective on animism is similar however, extends into the underlying concepts of "magic", (e.g., ancient cultures), and as being the basis of formal religions.
As far as stories "evolving" I would assume some probably have, although without having some original text or equivalent, to compare modern versions too, I guess it would be speculation, however probable, to say.
It is specualtion that such stories evolve, (although there is considerable evidence extant that many, many _other_ stories/old tales have evolved), but then it is also a speculation that they haven't. As you indicated, there would have to be comparative evidence available, (beyond two generations of oral traditions and interpreting cave drawings through current perspectives).