Early Iranians believed evil had to have a source outside of God, which led to the concept of an entity as powerful and utterly evil as God is potent and good. These two forces, good and evil, which have always vied for superiority, needed helpers in this struggle. According to the Zoroastrians, every entity had to take sides, from the cosmic level to the microcosmic self.

One of the results of this battle was that certain humans were thought to side with evil. Who were these allies of that great Evil Spirit? Women were inordinately singled out. Male healers were forbidden to deal...