"The origin of consciousness in the breakdown of the bicameral mind" by Julian Jaynes
"Left in the dark" by Graham Gynn and Tony Wright (and apparently, 2nd hand recommendation - "Return of the brain to eden" from the same authors)
Consider both science fiction rather than science; Jaynes is much more scientific and grounded, though it is still incomplete. Wright is much looser with facts and interpretations,
Still, both are thought provoking and worth reading in my opinion.