Why can vampires only drink human blood? [closed]

Question

Vampires are depicted differently in every work of fiction, but one thing mainly stays the same: they need blood to survive. Human blood, to be precise. Some stories add in the rule that they can also drink blood from animals and usually put vampires who make the choice of only drinking animal blood on a morally higher ground than the savages who harm humans.

In my setting I want to take this a step further. Vampires are offered two choices to get their blood-fix: either drink from humans, or eat 'blood-oranges', the vampire variant of the snozzcumber. This fruit looks nothing like an actual blood orange and tastes absolutely horrible to both human and vampire, making it tempting to take a bite from a human every now and then. Even when it is common knowledge to them that biting humans will result in either the victim dying of blood-loss or turning into vampires themselves.

To keep these two choices absolute, I want to rule out any other source of blood. For some reason vampires need human blood, and don't consider animal blood an option. They can't drink from other vampires either. Vampires are already vampires, it completely takes away the risk of turning them like with humans.

How can I explain that vampires only consider humans as possible targets? I'm looking for an answer that suspends disbelief, so it's alright if a solution delves into pseudo-science/occult territory.

Answer 1

Possible solution:

• Allergic reaction.

  When drinking nonhuman blood, it triggers an allergic reaction, e.g. sickness, blood clumping, and other stuff. This is because of the different components in human and nonhuman blood.

  The idea behind can be compared to the reaction of your blood, when your receiving an injection with a incompatible kind of blood.

• Not filling

  Human blood has a special component needed by the vampires, e.g. Vitamin V. It can only be found in humans and their nearest relatives.

  (Blond, busty virgins contain a maximum amount of Vitamin V at their age of 18, so I've heard)

Answer 2

You can postulate that, together with blood, the vampire absorbs the intelligence of the blood donor. Therefore if they want to stay intelligent, they cannot drink from any species other than humans. Blood orange are the evolution of drinking from humans: they remove the social stigma of neck biting (as suggested in the comments, they mimic the blood used to make them germinate), and being grown in garden, the owner can mix various intelligences (the musician's intelligence, the painter's, the mathematician's, the leader's, etc) to use on purpose, giving him/her a clear advantage on human drinkers (you never find a Mc Giver when you need one...)

Answer 3

Few, aside from the vampires remember this... but before the current age of man, in the dark eons before recorded history, a precursor of modern homo-sapiens climbed the metaphoric tree of knowledge, attaining for themselves a level of technology which matches and in some ways exceeds that of our current age. An ancient war eradicated those precursors and erased all signs of their civilization, leaving only one legacy which has endured thru to today...

Vampires.

Vampires are the surviving victims of a vicious bio-weapon which was released across the entire world during the last days of that civilization-ending war. It was a disease which broke the stability of its victim's genetic code; forcing them to regress back along their evolutionary path; devolving into grotesque hybrids of their genetic ancestors. A few "lucky" victims of that plague regressed into a hybrid of man and bat, and thus obtained the ability to drink blood. And in that blood was hidden their genetic salvation.

Vampires do not drink blood for sustenance. They absorb it to restore their crumbling genetic code; to remind their bodies of what it means to be human. Without human blood to beat it back, the bat side of them grows and becomes dominant; turning them into mindless, voracious beasts.

...which is where the blood oranges come in. Blood oranges are not a natural product. They were created by the now vampiric precursors to give themselves an alternative to drinking blood. The fruit contains two genetic codes; one which replicates the fruit and the other which is a dormant copy of the original precursor genetic code. The precursors created the blood oranges with the last of their technology, then collapsed into beast form which ironically didn't eat the oranges.

Only when homo-sapiens evolved, did the vampires' food supply once again provide them with the genetics building blocks for sentience; allowing them to push back the beast, rediscover the oranges and once again prowl the night as almost men.

Answer 4

Charles Stross's "The Rhesus Chart" has an interesting take on it. Vampirism is an effect of a parasitic entity hosted by the human being, which creates a need in the vampire (in the same way as some parasites change the behaviour of insects). When the vampire feeds, they create a link between their hosted parasites and their prey. The prey survives the feeding, but over a short period the hosted parasites eat the victim's brain/soul. If the vampire doesn't eat, ultimately the parasites will turn on them instead. The parasites need a human brain/soul, so the need they create in their vampire host is purely for human blood.

Answer 5

Blood Type matters

You could take it a step further, and say that not only does it have to be human blood, but the blood type has to match. Blood Oranges obviously are Type O (so universal) and vampires could probably tell blood type either by smell or first taste. Especially if Vampires lose the ability to create new blood cells themselves, this lends a bit of credibility to the notion.

Answer 6

The European source of blood need in vampirism originated from the gastric problems of high born. Which in turn came from incest and untreated STD.
So anyway, people suspected of vampirism could not eat regular food, or they appeared as not eating (starving look, slim face etc). For normal peasants when you went starving you died in few weeks. But the "vampires" lived.

Now, the people believed that there are for fluid in humans: black bile, yellow bile, phlegm, and blood. The blood was associated with vitality, spring and head (hence drinking blood from the neck). And because vampires were not having regular food (and animal blood was a kind of food) they draw a conclusion: if you don't eat but are still alive you need to have life force from something else. The only logical explanation was that they drink human blood.

Answer 7

Non-human blood is like taking in the wrong blood type during a transfusion, it can be deadly. LINK

If incompatible blood is given in a transfusion, the donor cells are treated as if they were foreign invaders, and the patient's immune system attacks them accordingly. Not only is the blood transfusion rendered useless, but a potentially massive activation of the immune system and clotting system can cause shock, kidney failure, circulatory collapse, and death.

Or, how about the nutrient value? You can fill up on non human blood but it does nothing for you, like candy. You cannot survive on it and it creates other problems.

Answer 8

Not every vampire myth requires the vampire to only consume human blood, but having said that its your world and in many stories they do so there's not reason not to have them do it.

In that case perhaps it is because vampires having once been living humans need human blood to enable their body to properly function, only human blood cells would be of the correct shape and size to properly travel through all the smaller blood vessels and capillaries in the body. There are several types of anemia such as sickle cell and vitamin B12 where blood cell abnormalities cause problems. Blood cells from other animals would not be of the the correct form to travel through the circulatory system fully.

This relies on a couple of things, that they do not digest human blood and break it down but rather absorb it in their body through their stomach and gut. Also they drink human blood in order to allow their undead metabolism to work, just as in human bodies blood allows the transport of oxygen for use in the Krebs cycle to create the energy the body needs to function. It would also require that for some reason in their vampire state they can no longer produce their own viable blood cells.

Answer 9

Depends on the nature of your vampires. Are they the result of an ancient curse? Or just magical creatures?

In the former case, the need for human blood is just part of the curse, and the harder to sell thing is any substitutive, like the blood orange.

If they are just magical beings that have existed as long as humanity... Well, it's the same, they need specifically human blood because that's how they are (yes, "because magic").

Actually, you don't really need to explain that
You see, the vampire is a pretty stablished creature. Their main defining trait is their need of human blood. Once the reader sees a close-to-classical vampire, that need is assumed and it's everything else (animal blood, blood oranges, no real need but a sort of addiction, etc) that have to be explained.

Answer 10

Let's assume that your vampirism is a product of some extremely rare disease (I'll call it Maledicto Sanguisuga). This disease is caused by colony of weird bacteria which binds itself to its host and transmits to another victim on very specific circumstances. The symptoms are rather bizarre as well:

• Extended lifetime of the host: these bacteria can rarely find a suitable host so surviving as long as possible within the body of current host is essential. Therefore these bacteria repair and revitalise host's body tissues and cells to the point that host's body doesn't need to consume any more food (actually, host shouldn't consume any food at all - who know what they put in there).

• Superhuman abilities: longevity is good but even undying host is not immortal. These bacteria are allergic to sunlight, which is why high speed (vampire's quickness) is mandatory. The host can get into a fight or get stuck in the trap, which is why high strength is quite useful as well (and let's throw a superhuman senses for good measure).

• Host is rather pale and skinny - these bacteria feed on host's blood, replacing it's cells with itself. Since host cease to produce new blood (he can't eat anything), he has to drink other people's blood (or blood oranges as the only suitable substitute) to keep his bacteria fed. Long periods of hunger force bacteria to cause pain to its host (motivating him to find food for bacteria) - hence the slips of sanity.

I know, it sounds like "nanomachines, son" explanation, but...

Answer 11

Use genetics!

Blood is basically water containing proteins, glucose & minerals used to deliver & distribute nutrients throughout the body of most mammals, we need something to differentiate human blood from that of other animals¹.

Something you could make use of is the fact that white bloodcells are an excellent source of DNA. You could make your vampires more parasitic and have them require fresh cells with plenty of easily accessible DNA in order to fix their own cells and thus bodies.

Consuming the blood of another animal² would result in their system using DNA from these animals and thus producing cells that might not work together with the rest of the system, effectively mutating them into grotesques that cannot sustain.

As for your blood-oranges: You will to have to create them in either a laboratory or in some magical alchemists workshop, thus there is no problem in making them carry either human DNA or some generic bits that the parasite can sufficiently use and combine with their own genetic material.

_{¹As you also mention in your question.
²Yes, humans are animals!}

Answer 12

Vampires do not Produce Enough Blood on their Own

The short idea is this - vampires are parasitic creatures with a trade-off: in exchange for the abilities they possess, their ability to produce blood on their own is hampered. The key word being hampered. They can/do still produce blood on their own, but at a rate that is slightly less then they require. Of course, you can adjust the rate they produce blood yourself to suit your story - anywhere from needing a top-up only rarely to every day.

Their Teeth Direct Blood Directly to their Veins (and/or "Blood-Bladder")

Rather than "drinking" the blood and extracting nutrients from their stomachs, the blood they steal from their victims via their fangs goes directly into their own bloodstream. One pesky problem with this approach is that if they need to drink 5-6 pints to kill a person they themselves would need to be down at least 5-6 pints... and they would be dead by then. And thus the "blood-bladder" is introduced; an elasticized internal vein that can swell to hold blood.

This direct transfusion process explains why vampires cannot drink animal blood. They literally use the blood they consume and (like people) are not compatible with other animals.

This mechanism has the added potential story benefit/issue of allowing vampires to neatly deal with (and possibly contract) disease, if you want to go that route. Have a bad flu? Go chomp on someone who recently got a flu vaccine and put their white blood cells to work. Tough luck if you eat someone with the flu though.

The blood-borne disease issue can also be sidestepped by simply noting that vampires produce excellent quantities of highly effective white blood cells that take care of pretty much any blood-borne entities that are not beneficial to the vampire. Perhaps their self-produced white blood cells learn from every white blood cell they injest, making older vampires much more resistant to disease than newer vampires.

The Blood Orange

Remember how we said that vampires do not produce ENOUGH blood on their own? Well, "blood oranges" contain particular enzymes that stimulate increased blood production. I would suggest that unlike human blood, blood oranges are probably consumed in the traditional fashion.

Answer 13

My understanding on why vampires need to drink human blood is because "the life of the flesh is in the blood". (Lev. 17:11a) Of course, not all vampires require blood. Incubi and succubi are considered vampires, but they rely on psychic energy.

Answer 14

This has idea has been touched in a number of works. The most popular reason is simply that human blood is the only kind that is sufficiently nutritious. Compare it to a human only eating cabbage. You'll survive for a bit, but cabbage won't keep you alive in the long run. In the same fashion, a vampire CAN use animal blood, but they can't live for sustained periods of time on it.There WILL come a time when they need human blood, no ifs, ands, or buts.

Answer 15

If you want an odd but interesting pseudo-science answer, then go with quantum nutrition.

Every object with mass has an effect on the spacetime around it. Certain objects bend space in just such a way a particular way that they have unique properties above and aside whatever the object is used for. Thus, human blood has a unique flavor and/or nutrition based on the manner in which human blood (or a component of the blood) bends spacetime. Perhaps a protein chain, or a peculiarity of the DNA or RNA sequences of certain blood types. This exact chain is not duplicated in anything but this one particular plant.

And that would give you exactly two sources of nutrition. And a species very likely to die out should anything (mutation, population drop, etc) happen to the food source.

Answer 16

Because of their ability to regenerate and heal quickly, vampires are very hard to kill. However, the vampire conversion process causes a flaw in their DNA, and so they need an outside template to use in order to repair cells correctly.

If a vampire feeds off of a plant or animal with non-human DNA, then there is a DNA mismatch which can cause rapid cell death. This is why vampires will get sick when they eat normal food. Their bodies try to incorporate this foreign DNA, and in the process causes stomach problems that trigger the vampire to expel the meal.

The part of the blood that has DNA is the white blood cell, and it has a pretty short life of 5-20 days. This would give an idea of how often the vampire would need to feed.

The real question is how the blood oranges work if it's the DNA that is important.
Say some vampire elder worked out a way over the long centuries to splice plant and human DNA, and came up with a hybrid that contains enough human style DNA that it can be eaten without making the vampire sick, and allow for a DNA template. It would be imperfect compared to real DNA, but if the important parts matched up then it would serve it's purpose. It could be that real DNA gives greater vitality, but a vampire with a conscience or who wishes to remain hidden could live off of it without problems.

On a side note, rapid cell regeneration would account for problems with vampires in sunlight, since sunlight contains ionizing radiation, and that can damage cells. If the cells are being damaged and rebuilt very quickly, it could cause metabolic problems when exposed, that they wouldn't have with artificial light.