The suave and sensitive Edward Cullen of Twilight may be the norm for vampires these days, but fictional monsters such as Dracula originally sprang from the fear of inexplicable diseases and the mysteries of death in the natural world.

So argues science journalist Matt Kaplan in Medusa's Gaze and Vampire's Bite: The Science of Monsters, an examination of monsters around the world and throughout history - the science behind their origins, and why they matter to us even now.

"When our kids ask for monster stories around the campfire, they are behaving in a way that is not dissimilar to lion cubs," Kaplan said in an email.

"Lion cubs play fight so they can test out their skills in a safe place where nobody is going to get maimed or killed. Monster stories serve a similar purpose, they allow us to face our worst fears without the risks that are normally associated with them."

Some are simple. The Kraken tales of mammoth monster squid, along with the Leviathan of the Bible, are most likely based upon the existence of real creatures such as whales.

The terrifying Medusa of Greek myths, with her hair made of snakes and a gaze that could turn things to stone, may have been distantly connected to the idea of fossils for ancient people, with the snakes in her hair an example of pure fear.

Though mentions of vampire-like creatures exist as early as ancient Greece, it took hundreds of years for tales of the creatures to gradually evolve into the haunting undead of more recent history.

Accounts of people found in their graves with blood on their lips and their stomachs seemingly full, as if they had just eaten, may be explained by simple decay, with gas buildup throughout the body sometimes pushing blood up from the lungs. Elongated canine teeth and fingernails was due to skin shrinking after death and pulling away, making both more prominent.

Later, greater awareness of contagious diseases such as influenza and tuberculosis - which could cause people who came in contact with the ill person to also sicken and die - further contributed to the myth. This was especially true due to incubation periods that weren't understood at the time, making it unclear how the diseases were being spread.

"One death would follow another in a dominolike progression," writes Kaplan. "In a morbid sense, these patients were literally killing their friends and relatives, but from their deathbeds rather than the hereafter."

But vampires have now undergone a radical transformation, a process that began with the publication of Bram Stoker's "Dracula" but has speeded up in recent years.

"If tuberculosis, influenza, rabies and bloated bodies are the human experiences from which Dracula came, how have we now ended up with the kind, honourable and handsome Edward Cullen?" Kaplan said.

For one thing, modern science has uncovered the mechanism of various diseases, which remain a fear but now appear as their true selves, as in stories such as "The Andromeda Strain."

Vampires have also become increasingly charming, transforming their original monster nature into something else.

"In a world where the seemingly most virtuous individuals all too often fall prey to vice, public interest in good souls battling their own bestial natures is higher than ever, and vampires provide exploration of this," Kaplan added.

In the future, fears are likely to focus on things like genetic manipulation - think Jurassic Park - and also from technology, with worries about what computers might do with true artificial intelligence looming large.

"What I find most interesting here is that these monsters really require human participation in their creation," he said, noting the popularity of films like Avatar and Planet of the Apes, where monsters are the heroes and the humans, monsters.

Why are we so comfortable with feeling elated as inhuman beasts rip apart people? I think a long, hard look in the mirror can provide a lot of answers," he said.