Other theories
You may subscribe or not to these theories. They have been stated because they exist but to most of our knowledge there are no serious proofs to sustain them.
The Hormone Theory
According to this theory, the vampire is the next step of human evolution. A genetic complex present inside our body but usually dormant get activated by a hormone brought in from an external source. The hormone transforms the victim's physical form and the new vampire will be able to inject the hormone into another victim.
The Fallen Angels Theory
This theory inspired from the Books of Enoch claims that vampires are the offspring of the union between the Watchers (Fallen Angels) and humans. When the Children of the Watchers had consumed all of the food available, they turned to mankind and began to eat their flesh and drink their blood. In another adjunct, vampires are the offspring of the daughters of Eve (female humans) and the Angel of Death sent by God on Earth. Vampires have the mission to control and thwart the demonic offspring of the fallen angels.
The Nanobot Theory
Nanobots, created either by renegade scientists or a race of reptilians, were introduced into a handful of human bodies in order to repair damaged cells. These nanobots performed so well that they rendered their hosts immortal. However, the Nanobots themselves are not immortal and must self-replicate by utilizing the iron atoms from the hemoglobin in the host's red blood cells. The result of this nanoreplication process is the constant need for sufficient supplies of blood. Unable to keep up with the demand, the host has no choice but to seek out blood from others. If the colony of Nanobots exceeds the host's ability to supply sufficient RBCs, some nanobots may migrate into another host, usually the next victim of the primary host's bite.
The Atlantis Theory
The Atlantans, in their quest to prolong life, have conducted biological and genetic experiments which end result was a new human that could live for centuries but had to drink the blood of humans in order to survive. Vampires have escaped the Great Flood as the Atlantans, not satisfied with the results, had buried them in an underground crypt.
The Alien Vampire Theory
Since H.G. Wells’ "The Flowering of the Strange Orchid" in 1894, there has been many writings and movies exploring the possibility of a space alien taking over a human body in order to live off the life energies of others. Those space aliens are some kind of parasites that control our mind and draw our vital forces. When they have exhausted the body, they look for a new host. In another adjunct, vampires do not come from outter space but from another dimension.
