There are tales in all folklore about werewolves , so what could werewolves have been ?Well maybe the story of the Wulver in Scotland can shed some light on it.
Wulver - Shetland Isles :
The wulver is described in Jessie Saxby's Shetland Traditional Lore as being a man with a wolf's head, with short brown hair all over him. He lived in a cave dug out of the side of a steep knowe, (knoll I think that is ) half-way up a hill. The wulver did not molest folk if they did not molest him. He was fond of fishing. A small rock in the deep water is known to this day as the "Wulver's Stane". He would sit there for hours, fishing for sillaks and piltaks. He was reported to have frequently left a few fish on the window sill of some poor person.
Briggs, Katharine. An Encyclopedia of Fairies. Chapter 9, pp. 445-446.
A Wulver is a kind of werewolf described as a man, covered with short brown hair but with a wolf's head. He lived in a cave and kept to himself and was not aggressive if left in peace. He was apparently to be seen fishing.
The ancient Celts believed that the wulver evolved from wolves, and that the Wulver symbolized the intermediary phase between wolf and man. Wulvers were considered to be kind hearted and would guide lost travellers to nearby villages. The wulver was an evil-looking, but harmless creature that looked like a man with a wolf’s head. The last reported sighting was early in the 20th century.
There are conditions such as hypertrichosis (excessive hair growth over the entire body) which would explain the Wulver. There is also a mental disorder called clinical lycanthropy, in which an affected person has a delusional belief that they are transforming into another animal, although not always a wolf . It is a rare condition. So were wulvers just a poor human with a condition that made them outcasts? It is a genetic condition and a place like the Shetlands centuries ago would be quite isolated and families would marry into each other passing the genes on. This would also explain the kind heartedness of the Wulver, not the aggressive werewolf of legend, but a man outcast due to his inherited condition.
Saxby Jessie (1932). Shetland Traditional Lore. Edinburgh, Grant & Murray. ASIN: B000O9XQ6M.