I think this has been a very interesting topic so far, and seemed to connect in a way to what I read in Joseph Campbell's first volume of Masks of God, Primitive Mythology.
There are a lot of ideas that get jumbled up in the book and don't seem to flow and transition effectively, but a couple of things are intriguing from standpoint of trying to imagine the roots of cultural superstition and spirituality. One thing he talks about is how the human life cycle must have seemed like an extraordinary enigma.
Assume for a moment that primitive yet thinking minds don't put two and two together and figure out that it's the combination of male and female that results in conception (and I believe there have still been societies up into modern times who didn't figure it out), but they're still trying to work out the cause and effect of the world around them, then all they can assume from what they observe is that females are the ones with the power of creation. They might as well conclude that the female body is a gateway from beyond to the Earthly existence, you enter or re-enter the world through that "creative magic." Burial rituals, which I believe is associated with early developing culture and intelligence, is described in the book as prepping the body of a dead person for their re-awakening, or their journey back to...wherever. Campbell also talks about how baffling it must have seemed to the primitive mind that females' cycles were syncronized with the phases of the moon; they are in tune with the known universe in an unknown, mysterious, "magical" way. The males were probably envious or fearful of the phenomenon.
I can't recall the particulars, but he goes through a loose narrative about males "hijacking" spirituality; understanding how fearful they felt, and how fear controlled them, they turned the tables and developed elaborate rituals to make sure that life continued to progress in a way that was desirable to their way of life (and themselves more particularly). Their part in the rituals were highly secretive, males only, and the knowledge they are to face in their rite of passage would terrify the females, so females are strictly forbidden, and their fear of the male rituals is cultivated.
Along a different thread, Campbell talks about Shaman as being the types of humans who were imaginative, but perhaps not the most physically able of a community. Here he develops a narrative where the less physical, yet highly imaginative types seize power away from the "survival and prospering of the fittest" mentality. Shaman are imaginative, storytellers, have a good sense of showmanship, and they learn what their stronger, tougher fellows fear. Exploiting that fear is the only way to carve their own niche in the community, a way of life that is not one of being jostled out of the way or tossed around. So they cultivated the appearance of having powers and knowledge over the unknown elements that the stronger people feared; and the strong ones finally feared him.
Another part of the thing with Shaman is their training would involve putting the body under extreme stress; starvation, exposure to heat, ensuring a lack of sleep (and sometimes a magic mushroom thrown in for a trip). All the kind of activities associated with having a revelation of enlightenment in the stories of plenty of Sacred religious founders. They are also the kind of thing results in hallucinations, with or without the mushroom.
Most of the above is a long winded exploration of using spirituality; harnessing the unknown and grafting a structure onto it for the purpose of...political power. There is a vein of cynicism toward organized religion and spiritual viewpoints on Joseph Campbell's part throughout the book, though his professed aim is to eschew common assumptions about spirituality and try to trace it's development throughout human history, trying to approach it as ruthlessly scientifically or objectively as possible.
Along another thread, Campbell talks about the Deification of humans; the God-Kings and Pharoahs. I can't remember how this aspect connected with the previous elements above, in terms of historical context. I was vaguely amused/horrified at the Deicidal practices of some of these cultures; in some ways it reminded me of my own ideas about effective leadership...a leader should be a servant to those he leads. My most effective leadership moments have emerged from efforts to serve a group I ended up leading. Of course, Deicide is an extreme situation of taking the matter out of the hands of the leader's own choice, regarding how much the leader is supposed to serve and sacrifice. Interestingly, the core of Christianity seems to conform with this pattern of Deicide in service to humanity. I've wondered since reading those passages from Primitive Mythology about the communal psychological drive to lift someone up, Deify and make them a King, and then sacrifice them for the good (or perhaps, satisfaction?) of the community. On a totally unrelated note, it makes me wonder if modern American pop-culture is a "safe" manifestation of the same communal psychological drive: we set up a Celebrity on high, put them on a pedestal, then we tear them to shreds when they become weak or vulnerable or meltdown (or whatever). I don't like the impulses I feel inside me when I see it happen, and I turn away.
I'm sorry if it doesn't really feed back into the actual topic, I can't really tie in what I've paraphrased above with the God concept taking root in early human thought and evolving to what it is today. Hopefully it's of some interest, but I can't fathom making these thoughts more coherent than they are as I've presented them. For what it's worth, I've found all of the long posts of everyone else in this topic to be gripping, thought provoking, and engaging reads.