I think that the bicameral mind hypothesis makes sense.

Oh, and the phenomena wherein the disconnection of the hemispheres of the brain results in strange cognitive artifacts such as being able to give two different answers to one question, even questions like "what is your favorite color," points to at the very least some kind of parallel consciousness. Another hypothesis is that one hemisphere is the "speaking" brain and the other is the "listening" hemisphere. That is, only one of the consciousnesses can talk -- and that's the one we call "me"; maybe it should be "us."