Paranormal Podcast recently had an episode about werewolves. I agree with most of what is said on the show. The basis of these stories seem to lie with early homo sapiens who had to compete with wolves and other wild animals for survival. As with most enemies, humans had some respect/envy for their animal rivals. Spiritualism and the desire to be like the animal seem to have been the basis for rituals to hunt/be like the animals.
The podcast's guest, Dr. Bob Curran, makes the claim that the desire to be like animals went from good to different to evil because of the spread of Christianity. However, a global look at stories of people who can turn into animals are almost always horror-like. American Indian legends found throughout the United States contain numerous mentions of skin walkers. The Anicent Greeks had King Lycaon who was turned into wolfman as punishment. Same thing for the various werecreatures in Africa.
Werewolves and the other werecreatures seem to be instead the manifestation of fear of an enemy within. Their is an English-legend that really backs this assessment up. A fox had the ability to turn itself into a human. It would use this ability to trick travellers into following it into the woods where the fox-man would eat the people. It took a wise old woman to lure the fox into a pub where the truth was revealed to finally kill the fox-man. Paranoia and fear of a fifth column have allowed a natural, ancient rivalry of animals to become horror stories of beast hiding in men.