Vincent van Gogh [Public domain], via Wikimedia Commons

If someone bit by a vampire turns into one when they die, how long until everyone is vampires?

Short answer: It depends how smart the vampires are. Humans could last a month. Or two hundred years.

Long answer: Bram Stoker’s Dracula is an excellent book, and it codified the modern idea of a vampire as having a certain set of traits, such as

  1. Immortality, and regaining youthfulness by drinking human blood
  2. Immunity to conventional weapons, but destroyed by sunlight and holy symbols
  3. Telepathic connection to bite victims
  4. Cannot enter homes without an invitation
  5. Shape-shifting and manipulation of weather
  6. Victims of bites become vampires upon death

Among many other awesome abilities and weaknesses, it’s that last one that’s important. Since the victim of a vampire bite becomes an immortal vampire upon their death, the number of vampires is strictly increasing, requiring ever larger numbers of humans to feed them. Within a short time there will be no humans, only vampires, and with no humans to feed on they will go extinct.

Put simply, vampirism is unsustainable.

How unsustainable? Let’s do some math. I’m going to assume a vampire has similar caloric requirements to an average adult, about 2000 Calories a day, and I’m going to ignore any sort of extra caloric requirements for using their magic powers.

A standard blood donation is a half liter, and assuming human blood has similar nutritional qualities to lambs’ blood, that would mean a typical donation contains about 375 Cals [1]. That means that a vampire will need to drink about 5 Liters every night, which is surprisingly equal to the amount of blood in a human body.

Therefore, each vampire in the world could conceivably drain one human every night, thus killing that person by exsanguination (“death by blood loss”). This doubles the population of vampires every night. In just 32 days, starting from one Count Dracula, over half of the people on earth would be vampires. On that 33rd night, they’ll realize that the feast can’t go on, as there wouldn’t be enough blood to go around.

But suppose your first vampire is smart. Suppose that vampire happens to know some math. Maybe he was a theoretical astrophysicist before he became an undead bloodsucker, and he wants to delay the vampirization of mankind (Don’t judge me, I bet you have a zombie-plan. How’s that less weird than me having a vampire-plan where I’m patient-zero?).

The question now becomes, “How long can we drag this out for?” If a human can safely donate a half liter of blood at a time, maybe once per month, then our hero villain will need to feed from about 10 different people every night. Since they’re not dying just yet, he can return to them next month, and they can live long happy lives (aside from the part where they’re vampire-chow once a month). This single vampire now needs 300 people to support him, who he’ll cycle through over the month. After, say, 50 years of this, these people will die of natural causes, becoming vampires themselves.

So instead of doubling the vampire population daily, it’s now going to increase by ×300 once per generation. So in the first generation there is 1 vampire, but in 50 years there are then 301. In another 50 years there are 90,601, and in another 50 after that there are 27,270,901. At this point, it takes approximately the blood of nearly 8 billion people to support them. Assuming population growth keeps up, it may be possible for humans (and thus vampires) to survive for one more generation, getting us 200 years in the future.

Or, that first vampire could just recruit a mortal to clean up after him, killing all the extra vampires he makes, and in that case, Count Dracula could live indefinitely.




cover image credit: Wikimedia Commons


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