Although records of intense spiritual experiences in nature exist throughout history, the phenomenon remains a little-investigated question. This article is the lrst in a series describing empirical lndings on intense spiritual experiences in nature. Three data points were established including:(1) a cognitive analysis of forest attitude research interviews; (2) a cognitive analysis of nature authors who write about forests; and (3) a broad review of literature drawn primarily from research in neuroscience, psychology, medicine, consciousness studies, and philosophy. The lndings suggest that intense spiritual experience in nature has two variations: mystical and traumatic. The positive (mystical) and negative (traumatic) variations share seven physiological and psychological characteristics, with each characteristic providing adaptive, evolutionary advantages. Although partial and preliminary, the data offer compelling evidence demonstrating the existence of certain basic properties of the role of nature in intense spiritual experience. The lndings suggest that natural selection may favor intense spiritual experiences in nature.