Alkaloids in plants, especially hallucinogenic compounds such as psilocybin, dimethyltryptamine (DMT), and harmaline, may be the chemical factors in the diet of protohumans that catalyzed the emergence of self-reflection in humans.
The action of hallucinogens in several common plants has improved our information processing activities, or environmental sensitivity, and thus contributed to the expansion of human brain size.
At a later stage in this same process, hallucinogens acted as a catalyzer in the development of the imagination, energizing the creation of internal ploys and hopes that may well have synergized the emergence of language and religion.
Talamasca & Ivan Castro – Marijuana Reaction