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.
peoples who have culture and genes unchanged in the last 3000 years
To quote the pdf you dug up:
Anthropologists once had the assumption that if you find a hunter-gatherer tribe nowadays, it
is in a stone age similar to a pre-civilized era. This is not true. Each has had a history just as long
as we have, and perhaps a complicated history of going through a bicameral phase somewhere...
Jaynes postulates, in passing, a genetic basis for bicamerality (which I assume you mean by "this kind of thinking"), for instance p.311: "...there was probably a strong genetic basis for this type of remaining bicamerality. It is, I think, the same genetic basis that remains with us as part of the etiology of schizophrenia".
Does that help ?
To defend or critique Jaynes properly (well, any better) I'd have to reread him. I picked up his book out of curiosity a few years ago when I was going through Dennett's consciousness books; he cites Jaynes approvingly a few times. However, Dennet does not directly cites his bicameral theory, just his contention that language (more specifically "a capacity for self-exhortation") played a key role in the development of minds capable of formulating plans. The other hook was Stephenson's "Snow Crash", which features Jaynes' theory prominently.
http://www.rifters.com/crawl/?p=791