Both the christians and muslims executed as many magi and their followers as they could get their hands on. Since the priesthood was inherited through descent, these programs wiped out entire genetic lineages.

How this relates to the "God gene" recently discovered by geneticists is unknown, but it might have been a way to permanently eliminate from humanity those with the drive and capability to understand higher things. Being a shaman or magus is related directly to the ability to repidly achieve trance state. If you eliminate the capability of receiving higher information from the population, then you corner the market. It was all about POWER which is exactly the last thing that spirituality should be about.