I've often wondered if ancient religions, and even those in the modern world, are started by people suffering from schizophrenia?
I doubt it.
I think the core influence which results in religious thought (especially in primitive cultures) is the natural tendency of the human mind to anthropomorphize. When the human mind applies human intent and motivation to aspects of the natural world, supernatural beings result almost automatically. Once these ideas are formed, cultures amplify them through other natural human behaviors (like embellished stories and other motivations designed to give power to the individual telling the stories).
People with schizophrenia (and other unusual behaviors) may have reinforced some people's belief simply by providing a fertile ground for people pre-conceived notions to grow, but I don't think schizophrenia is the root cause.
The ideas on Bicameral thought are interesting, but purely speculative. I don't see how anyone could come up with any evidence to support the idea that human thought originated in that form. But we'll probably never know for sure.
I think you are wrong... First of all, the precursors of religion are animism and naturalism, last first, I guess.... But the words you use, idea, notion, conceived, that is: concept, all of which is essential to thought, like essence itself is a spiritual quality... If you can imagine a cap of steel, weighing 100, 000 kps, and wish to place that gently atop the pyramid of Cheops, you do it first by thought as the mainipulation of matter through its essence, the idea of it... All things we know, we know through the idea of them, and the original gods were the ideas of material things...So the idea of human thought originating in this form or that is nonsense when thought is form/idea/notion/concept...
What Jahnes was saying and the title of the book says, is the origin of consciousness in the breakdown of the bicameral mind... When ever we think we can be conscious of the weighing of facts against opinion, desires against realities, knowledge against speculation, thought against emotion, and most of us are conscious of these directions of our behavior as conscience, or reason... Because of our organic complexity it is possible for us to be of two minds consciously...Schizophrenics seem, like primitives, seem to locate one phase of consciousness outside of themselves as in the burning bush of Moses, or the god whispering wisdom into the ear of Hammarabi... Those who recognized this attribute as internal to themselves, who did not have to consult a fetish, or enter some dream state to reach a conclusion had the genetic advantage... Those people did not live in their nature as animals do, but above their nature as we do, usually; because there are many throwbacks...