Ok this is my first blog so might not be the best.So if you dont believe in vampires or lycan or dont have an open mind about things go away.Now on with the blog ok so do you belive in demons and angels good no them shoosh.
Ok so we all know you can make pacts with demons and devils so what if a man made a pact with the devil/demon to gain imortality but to sustain it he had to drink the blood of humans and in the process he gained demonic powers but kept his human form and then he had manny of spring creating a whole different species of humans vampires or maybe a human has to make a pact with a demon or the devil to have this power.The same could go with werewolfs but maybe there is a process.
My other theorie is that all demons but maybe a race of demons one had wolf charectistics and the other vampire charectistics that were at war with each other and to get the upperhand they impregnated woman to create more of there kind starting another race of beings.
So there you have it folkes maybe not the best but it is a more legit theorie the ones i have heard.