At the foundation of Julian Jaynes's bicameral theory found in "The Origin of Consciousness in the Breakdown of the Bicameral Mind" (OC) is the idea that prehistoric people had a different kind of mentality to modern humankind; they were not conscious. And the theory does not view consciousness as an attribute of evolution since evolutionary traits take millions of years to develop. The theory views consciousness as a recent characteristic that developed in time measured in thousands of years and not millions, being revolutionary.
Modern people, instead, consciously consider the options, using thought, which is heard as inner dialogue and, for us, the whole brain-working exercise of decision-making is patently encapsulated in our brain cases.
Of course that may not be the case for modern-day individuals who do experience auditory hallucinations.
In "Reflections on the Dawn of Consciousness" (RDC) Marcel Kuijsten comments that "The issue of the complexity of Jaynes's theory and its multi-disciplinary nature is one possible reason for the absence of greater formal discussion on the topic. But perhaps the most common reason for the rejection of Jayne's theory is due to a misunderstanding (or complete lack of awareness) of Jaynes's definition of consciousness; there have have been countless times I've heard someone offer a strong opinion on Jaynes only to discover they've never read his book."
Kuijsten continues "The notion that ancient civilizations were populated by unconscious people generates a knee-jerk response that the theory is "preposterous" primarily because of the deeply ingrained but mistaken notion that consciousness is necessary for the majority of higher mental processes (and even basic sensory perception), coupled with the tremendous difficulty in comprehending a mental state without an internal dialog for anyone that has one. ... Put simply, critics reject the notion of pre-conscious civilizations prior to 1200 B.C. based on *their* ["italics"] definition of consciousness, not Jaynes's."
... to be continued