Morsella has gone back to basics. Forget art, symphonies, science. Forget the step-by-step learning of complex tasks. Those may be some of the things we use consciousness for now but that doesn’t mean that’s what it evolved for, any more than the cones in our eyes evolved to give kaleidoscope makers something to do. What’s the primitive, bare-bones, nuts-and-bolts thing that consciousness does once we’ve stripped away all the self-aggrandizing bombast?
Morsella’s answer is delightfully mundane: it mediates conflicting motor commands to the skeletal muscles.
I found this interesting pdf of a discussion involving Jaynes (and Dennett) and it makes clear what he believed, which was that the change was mostly cultural, and that uncontacted tribes might be bicameral, but there were none left. ( I'm not sure this is true - anyone reading this have an anthropologist handy ? ) Also contains a very odd fact (?) about children.
EDIT: Oops, didn't notice it was on Jaynes' own website. So presumably quite a lot more stuff there.
http://www.rifters.com/crawl/?p=791