Curate, connect, and discover
This is gonna be a mish mash of cultures and ideas so bare with me. In eastern Europe (specificly slavic countrys) the vampire was an almost ghostly spirit rather than our common undead sexy friend. They were trixters to some extent, spread disease but in the way rats do rather than the specific bite we know. They also didn't consume blood. So this is the technical truth aspect of this idk 'theory' (but more headcannon I suppose). From this, I headcannon, it evolved into two specific paths: the vampire as we know and the seer. Both evolved to revolve around blood since blood is commonly seen as a holder of the human spirit and life force making it a very powerful energy source. Vampires evolved specifically as almost undead creatures, focusing on that ghostly aspect and almost making the souls haunt the dead body in such a way that it becomes 'imortal'. The sucking of blood is to create a constant source of energy to power the 'possession' and inturn their existence- like food for us. The 'infectious bite' then becomes a combination of corpse germs and supernatual infliction that continues to create vampires- something their ancestor obviously did not have due to the lack of biting and corperal form. on the otherhand, seers found their powersource in blood by creating their own. Specifically in having a functioning human body. The living body acts as a conduit for the supernatural power wich is displayed by divination and prophecy, what which ghosts being conected to the past and human life being seen as something of the future. This ghostly ancestor also explains why Ethan can see ghosts when touching their objects, he's channeling that energy. Of course if having a living body was such an easy way to have blood the vampire would have done it too, the problem with using your own body as a conduit continuously is that it starts to degrade over time either with natural circumstance like being old as shit and dying, or your body contracting ilnesses. It's has it's ups and downs. anyway the idea of a common ancestor is so intresting to me, especially since in the few mythologys I research prophecy and disease are strangely commonly linked. And I mean blood has ALWAYS been apart of seeing the future, think of literally any form of animal sacrifice amongst religions. Or how in some underworld storys the souls must consume the blood of a sacrifice (not necessarily human!) to be able to comunicate.