Stephen,
Intriguing speculation!  Thanks for sharing your thoughts.

A few years ago I read a fascinating book by Dr. Frederic Schiffer:  "Of Two Minds:  The Revolutionary Science of Dual-Brain Psychology".  It reviews several of the experiments over the years where the corpus callosum was severed or other cases, where the existence of two separate minds becomes evident, and the issues related to that; how PTSD and other traumas can lead to disintegration of the two minds, and how specific therapies (including special glasses) were used by Schiffer to help clients reintegrate.  You may want to take a look at his site, http://www.dualbrainpsychology.org/.  

I think Bishop John Shelby Spong has also advocated the idea of Adam and Eve as representing the onset of consciousness as we know it today (though I don't think the idea was original with him either), though more from an evolutionary perspective than a specific development associated with written language.