The great majority of scholarly definitions of "religion" center around some notion involving experience or awareness of a supernatural dimension (forces, entities). This sense of the supernatural has been found in virtually all human societies extending back into paleolithic times. Advances in neuroscientific research technology have made it possible to assert that phenomenal experience is in fact a form of brain activity; the two are identical. This naturally leads us to inquire as to why and how a brain evolving to serve the needs of survival and replication in a harsh natural environment should have developed the capacity and evident propensity to generate a sense of the supernatural. Psychology has recently identified a set of three primitive interpretive modules dedicated to generating a sense of causative essence. These modules are located in areas of the brain whose representational output can be experienced as non-material, like the stream of thought, rather than as external physical landscape. These non-physical neurophenomenal essences are identical to the three forms of otherworldly spirit essence found throughout human religious history, and they form the basis of the multi-layered neurophenomenal complex comprising the sense of the supernatural.