A professor at the University of Florida has proved that vampires couldn't ever have existed.
Vampires supposedly feed on human blood, and once bitten, a person turns into a vampire and starts feasting on the blood of others. If on Jan 1, 1600, the human population was 536,870,911 and the first vampire came into existence that day, then bit one person a month, there would have been two vampires by Feb. 1, 1600. A month later there would have been four, and so on. In just two-and-a-half years the original human population would all have become vampires with nobody left to feed on.
If mortality rates were taken into consideration, the population would disappear much faster. Even an unrealistically high reproduction rate couldn't counteract this effect.