@xris,
As for our savage nature - I don't mean, of course, that "culture" is only about manners (it isn't, even in the most refined or well-living societies). What I mean is that since we became reflective creatures, we cannot assume anymore that we even know what our "nature" is. And of course, even people in the most horrible situations don't always forget what they believe in; I don't think they are any better or worse for this reason (I think behaviour in such circumstances is "unjudgeable"), but they are no less "natural": simply, our nature is now a part of our culture, or vice versa, I'm not sure...
Regarding our ancestors, I agree that it seems plausible for them to assign magical powers to natural elements and forces, but the idea of a Creator seems to me way too abstract to arise around the bonfire. Actually, even the idea of monotheism seems to me to be so, Creator or not.