h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Lycanthropy
(From Greek lykos, ;wolf ; anthropos, &;man, mental disorder in which the patient believes that he is a wolf or some other nonhuman animal. Undoubtedly stimulated by the once widespread superstition that lycanthropy is a supernatural condition in which men actually assume the physical form of werewolves or other animals, the delusion has been most likely to occur among people who believe in reincarnation and the transmigration of souls.

Usually, a person is deemed to take the form of the most dangerous beast of prey of the region: the wolf or bear in Europe and northern Asia, the hyena or leopard in Africa, and the tiger in India, China, Japan, and elsewhere in Asia; but other animals are mentioned too. Both the superstition and the psychiatric disorder are linked with belief in animal guardian spirits, vampires, totemism, witches, and werewolves.
The folklore, fairy tales, and legends of many nations and peoples show evidence of lycanthropic belief. Stories of men turning into beasts go back to antiquity.
In parts of ancient Greece, werewolf myths, presumably stemming from prehistoric times, became linked with the Olympian religion. In Arcadia, a region plagued by wolves, there was a cult of the Wolf-Zeus.
Mount Lycaeus was the scene of a yearly gathering at which the priests were said to prepare a sacrificial feast that included meat mixed with human parts. According to legend, whoever tasted it became a wolf and could not turn back into a man unless he abstained from human flesh for nine years.

The Romans also knew of this superstition. Anyone who was supposed to have been turned into a wolf by means of magic spells or herbs was called versipellis (&;turnskin& by the Romans.