Not everyone agrees about the evolution of witchcraft in Europe. Some historians believe it developed out of the old fertility cults that worshipped a mother goddess. Others think that the idea of witchcraft was all superstition—when people could not explain an unpleasant event, they blamed it on someone whom they labeled a witch. Still other researchers say witchcraft stemmed from a wide variety of practices and customs including Paganism, Hebrew mysticism, Celtic tradition, and ancient Greek folklore.