"Neuroscience has begun to reveal some fascinating things about how the brain works, shedding light on the concept of personal identity, the data-handling limitations of the central nervous system, and the way that the brain smooths over its liabilities and discontinuities to sustain a sense of unified consciousness. We are beginning to realize that each of us really does contain multitudes, as Walt Whitman put it, and that the chorus of voices within was built up over eons of evolution, like geological strata in the or the ."