From countless depictions of "Dracula" to recent movies like "Twilight" and "New Moon," the vampire has been a staple in books and film. But is there a scientific basis for the folklore? Is there fact behind the myth of the blood-sucking creature of the night?

Decomposing bodies that leaked blood must have frightened gravediggers in the past. Tropical diseases and insects that suck blood, leaving corpses wasted and desiccated, must have seemed scary to other cultures. It's a short jump from fearful to superstitious, and there are clear biological and anthropological conditions that likely led to these fears.

Applying science to a mostly fictional creature is nothing new, says Dr. Katherine Ramsland, who teaches forensic psychology at DeSales University and wrote the book, "The Science of Vampires." Addressing the origins of the myth, she asks:

"Does it derive from mythology that addresses a basic fear of death, a lack of knowledge about body decomposition, an undefined disease, or perhaps the symptom of a mental illness now known as 'clinical vampirism'? That is, do these narratives express some society's need for myth, or might a vampire tale be an attempt to explain a frightening phenomenon actually witnessed?"

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To find the truth behind the stories that fuel TV shows like "The Vampire Diaries," we turned to science. We went straight to the scientists themselves — biologists, anthropologists and physicists — to find out once and for all whether vampires could have existed, and how accurate today's movies might be.

Avoiding sunlight: Several elements of the vampire legend are based around facts, artfully combined into a scary whole. Vampires are commonly depicted as creatures of the dark, being highly sensitive to sunlight. This is the case for people afflicted with porphyria, a well-known condition that makes one allergic to the sun. When exposed to the sun, people with porphyria develop burning blisters and swelling of the skin.

Porphyria is extremely rare, of course, but not so its milder cousin, polymorphic light eruption. This type of allergic reaction is characterized by the formation of bumpy and itchy rashes on sun-exposed skin. But it's not actually an allergy to the sun, rather an immune reaction.

Immortality: Dracula is commonly regarded as not just long-lived, but literally immortal. Ramsland thinks there is science to explain this aspect of the myth, noting research on what scientists call "immortalized cells." The aging process is partly predicated on the lifespan of our cells; as long as they continue dividing, we remain young, and structures in our cells called telomeres play a part in cellular division.

What controls the telomeres? Ramsland explains that "through the activity of an enzyme known as telomerase, the youth-preserving activity of the telomeres can be extended. In other words, there's an actual chemical in our cells that may hold the secret to eternal youth, and if so, it may explain how vampires can live forever."

Drinking blood: Mosquitoes, bats and other creatures drink blood, but humans rarely do — unless they have an iron deficiency such as anemia, notes Dr. Manuel Alvarez, managing editor for health at FoxNews.com. Those suffering from iron deficiencies could feel the need to rush out for an extra side-helping of iron-rich spinach … or may opt to eat an extremely bloody steak.

Craving iron and feasting on human blood are very different, of course. But Dr. Manny notes that pica, the pattern of eating non-foods or even blood, can result from anemia. This may not explain the vampire mythology, but it could explain one of the characteristics associated with the creatures.

Killing humans: Physicists Costas J. Efthimiou and Sohang Gandhi argue a good case against vampires, based on the hard facts of physics. In their 2007 paper "Cinema Fiction vs. Physics Reality: Ghosts, Vampires and Zombies," The pair work out a mathematical formula to describe the number of humans left after x months of vampirism spreading through a population of size n: x – 2^n + 1.

"... we conclude that if the first vampire appeared on January 1st of 1600 AD, humanity would have been wiped out by June of 1602, two and a half years later," the paper explains. "We conclude that vampires cannot exist, since their existence contradicts the existence of human beings. Incidentally, the logical proof that we just presented is of a type known as reduction ad absurdum, that is, reduction to the absurd."

That may be hard science, but it's hardly as entertaining as the fiction.