Mind-altering substances, according to many of the essays in this book, have played a major part not only in cultural development but also in human brain development. Researchers suggest that we purposely enhanced receptor sites in the brain, especially dopamine and serotonin, through the use of plants and fungi over a long period of time. The trade-off for lowered functioning and potential drug abuse was more creative thinking--or a leap in consciousness. Experiments in entheogen use led to the development of primitive medicine, in which certain mind-altering plants and fungi were imbibed to still fatigue, pain, or depression, while others were taken to promote hunger and libido. Our ancestors selected for our neural hardware, and our propensity for seeking altered forms of consciousness as a survival strategy may be intimately bound to our decision-making processes going back to the dawn of time.