The relationships among natural and drug-induced alterations of consciousness must be understood from an evolutionary perspective. This reveals altered consciousness to be related to endogenous mechanism, which are triggered by both ancient evolutionary adaptations and more recently acquired propensities to use exogenous sources of substances to alter consciousness.
John Rush, Entheogens and the Development of Culture: The Anthropology and Neurobiology of Ecstatic Experience
culture, entheogen, hallucinogenic