^It is a single theory, and admittedly, it sounds damned
crazy, but the author (Julian Jaynes) makes his case, and I'm only a third of the way through. His theory is that consciousness in humans evolved only around 3000 years ago, and that prior to this we functioned with bicameral minds, with one hemisphere of the brain issuing commands in the form of auditory and sometimes visual hallucinations, and the other hemisphere acting out those commands without any question. He posits that this is the origin of religion, and that illnesses like schizophrenia are linked to this recent past. He uses sound neurological and psychological evidence, as well as literary evidence from ancient texts to support his theory, demonstrating how non-conscious people could develop functioning societies. Yes, it sounds wild, but a lot about the brain is wild. The book is a little technical, and a background in either neuroscience or psychology is beneficial in reading it, but I think a layperson would get through it fine. It is a fascinating idea!