I have argued that every human being is born with an innate drive to
experience altered states of consciousness periodically -- in
particular to learn how to get away from ordinary ego-centered
consciousness. I have also explained my intuition that this drive is a
most important factor in our evolution, both as individuals and as a
species. Nonordinary experiences are vital to us because they are
expressions of our unconscious minds, and the integration of conscious
and unconscious experience is the key to life, health, and spiritual
development, and fullest use of our nervous systems. - Andrew Weil,
M.D.