Here's how I thought vampires came to be:
When your sock disappears in the dryer, the sock has actually been possessed by a grumpy laundry spirit who decided long ago that it wasn't cut out for cleaning peoples' clothes. So the laundry spirit dresses up in your "missing" sock and flies to the moon, where it works at a strip joint to pay for vampire college.
But the laundry spirit (Melvin) experiments with drugs and sex until it loses its original dream of being a vampire. It splits hairs, keeps all its eggs in one basket, says never, and generally indulges in unwholesome behavior. Finally, Melvin discovers religion and decides to study Catholic Vampirism, which I'm sure is in one of Anne Rice's novels. He graduates fifteenth in his class (Professor Skywalker always picked on him) and ventures back to earth, where he bites people in the neck and avoids garlic because the college cafeteria served cloves every day.
But I might be wrong...