Tales of vampiric creatures have been part of our culture for centuries. Often steeped in fantastical mythos, more modern fictional accounts strip away many of the incredible elements and try to fit the vampire into the realm of sci-fi.

Guillermo del Toro and Chuck Hogan’s upcoming TV series The Strain, based on their novel trilogy, attempts a very realistic approach to the vampire. While I won’t say enough to spoil anything for you, it involves a virus, and the vampire’s entire biology and physiology have been well thought-out.

But let’s build our own version of a realistic vampire, based on scientifically sound principles and what we observe in nature. We’ll start with the basics: our vampire will be a living (not undead) creature – a mammal and cousin to the human. Perhaps we shared a common ancestor with the vampire, but we evolved along different paths according to a predator-prey evolutionary track. Let’s call our race the homo vampiris.

1. Sun vulnerability

Let’s toss out the notion that vampires burst into flames once exposed to sunlight – that has far more to do with the mythos of vampires being evil and thus destroyed by something seen as pure, holy, or “good” as the Sun.

Instead, let’s consider the fact that the Sun is actually harmful to most creatures, given the right conditions. Humans around the world get sunburned every day, and millions contract skin cancer every year as a result of UV exposure.

What is a sunburn? Though we often don’t think of it this way, it’s actually a radiation burn that causes cellular damage. The Sun is constantly bombarding us with deadly ultraviolet radiation, and the Earth’s ozone layer filters out most of this harmful light. But what about the radiation that makes it through? The vast majority of it is dissipated by melanin, the pigment that gives our skin color. People with darker skin tones – that is to say, more melanin – have been found to be able to handle sun exposure better than fair-skinned people, who tend to burn more easily. But what if someone didn’t have any melanin at all?

That condition is known as albinism, a disorder that a person or animal is born with and is passed down genetically. In albinos, even the irises of the eyes lack pigment, which is why they appear red: you are seeing straight through to the retina. Normally, the iris contracts and expands to let more or less light in – this is why your pupils appear dilated in dim light, but much smaller in bright light. In the case of an albino’s iris, since it is transparent, it cannot effectively block the light entering the eye. Because of this, albinos tend to have difficulty seeing in bright light, and many even experience discomfort or pain.

So the first trait we’ll give our homo vampiris is the genetic condition of albinism, which grants them pale skin, white hair, red eyes, and an extreme aversion to sunlight.

2. Superhuman senses and strength

Vampires are always described as possessing superhuman qualities, both physical and sensory. Let’s start by addressing the former.

While a fictional vampire’s strength often comes from supernatural sources, we don’t have to resort to any of that poppycock – it’s entirely possible for a human-sized creature to have incredible strength. Take the orangutan, for instance, which stands four and a half feet tall, weighs about 150 lb, and yet is said to be seven times stronger than a human (that exact figure is contested, but what isn’t is the fact that apes are stronger than humans).

Why are they stronger? The answer lies, once again, in genetics. Scientists have identified genes that contribute to the development of certain key muscles in apes and found that they are deactivated in humans, barring exceptional athletes. Could it be that because we evolved to rely more on our brains than our brawn that we’ve genetically lost the ability to be as strong as other apes?

Needless to say, our homo vampiris will not have suffered the same evolutionary fate and would retain superhuman strength.

As far as heightened senses are concerned, nocturnal animals generally have highly developed senses of hearing, smell, and night vision. Not only would the homo vampiris have to be a nocturnal hunter due to its albinism, but it would also gain a distinct advantage over its prey of choice, due to a human’s poor ability to see in the dark. Lions prefer to hunt at night for the same reason.

Beyond the regular senses, many creatures have adapted the ability to locate prey in the dark using chemical detectors. Certain snakes and – surprise, surprise – vampire bats can even detect infrared radiation, allowing them to “see” body heat. We’ll give our homo vampiris such a “sixth sense” to make it the perfect hunter of man.

3. Feeding

Blood is rich in proteins and fats, and many creatures live entirely off a diet of blood. These hematophages, such as the vampire bat, tend to be parasites. While it may seem a natural fit to make the homo vampiris a parasite like in The Strain, that doesn’t quite fit the picture we’re building here.

A parasite is generally much smaller than its host and will often live or feed on its host for an extended period of time – without killing it. A lamprey, for instance, can feed on a shark for a long time without risking its host’s death. Relative to the shark, the smaller lamprey requires a lesser amount of nourishment to survive. According to Kleiber’s law, metabolic rate scales according to body mass. In other words, the bigger a creature, the more energy it needs.

The energy content of blood is about 900 calories per liter, and the human body holds roughly 5.5 liters of blood. A human needs about 2,000 daily calories to maintain its weight, and as per Kleiber’s law, a vampire would have roughly the same requirements, which comes out to 2.2 liters of blood per day.

How much blood can a human afford to lose before it dies? A healthy person can endure up to 15% blood loss without serious concern, up to 30% blood loss with visible skin pallor, and up to 40% while going into shock. Beyond 40% blood loss, the person will die unless extreme resuscitative measures are taken.

The math just so happens to work out that 40% of 5.5 liters is 2.2 liters, so for a vampire to get his daily blood requirement from a human, he’d have to bring him to the brink of death. Alternatively, he can safely feed on two or more humans.

But here’s the stickler: blood isn’t a nutritionally complete substance. It lacks sufficient vitamins, minerals, fiber, carbohydrates, and essential fatty acids to be a balanced food. Vampire bats are able to live off blood alone, but in order to get all the nutrients they need, they consume an incredible amount of blood relative to their body weight. A typical bat can drink over half of its weight in blood in a single feeding. For a 150 lb vampire, that would be about 75 lb of blood, which works out to roughly 38 liters – seven humans worth of blood.

While we can try to work out rationales that explain how vampires can sustain this degree of food intake without wiping out vast swaths of human population, it’s much easier to simply drop the concept that vampires are parasites entirely – they’re predators. Parasites evolved means of feeding that go largely unnoticed by their hosts because the host would otherwise easily be able to overpower the parasite. A vampire is stronger than a human, so it has no need to be discrete. A lion doesn’t quietly nibble on a gazelle’s thigh – it savagely rips out its throat.

Given a vampire can easily subdue a human, there’s no reason we can’t have our homo vampiris supplant its diet with flesh. In fact, many hematophages don’t exclusively rely on blood as their sole food source. Blood can still remain a vital part of the feeding process, but by getting some flesh in there as well, we’re cutting down tremendously on the amount of blood – and thus humans – a vampire needs a day to survive.

And why only human blood? Well, we’ll have to relegate that to societal reasons. In human culture, eating other humans is taboo. Maybe in our vampire culture, feeding on anything other than a human is taboo.

4. Immortality

Immortality is a trait often ascribed to vampires. In biology, the concept of immortality does exist – effectively, your body stops degrading over time. In fact, there exist some organisms on this planet that are immortal, including some jellyfish and possibly even lobsters.

Biological aging is nothing more than the gradual deterioration of our cells. Over time, our cells lose the ability to reproduce, so there are no fresh cells to replace cells that become damaged or simply undergo “normal wear and tear.” This can be extrapolated to our organs, which can no longer heal or function as well, until we eventually die of “old age” – which is actually the failure of some vital organ.

Research is currently underway to find ways to biologically engineer immortality into human beings, since we know – from nature – that it is possible. While we don’t appear close to making such a breakthrough, there’s no reason our vampire cannot be one of nature’s creatures that evolved to be biologically immortal.

5. Regeneration

Vampires are often depicted as possessing an incredible capacity for rapid healing and even the ability to regenerate lost body parts. Biologically, this presents little issue to us. Salamanders and newts are able to regenerate limbs, tails, jaws, eyes and a variety of internal structures. After suffering a wound, cells become activated and rebuild tissue and organs to their previous state.

Even human beings have demonstrated limited regenerative capabilities, such as the ability to regrow lost fingertips, and scientists are actively working to find ways to increase mammalian regeneration. Our homo vampiris could have natural regenerative properties that would make them especially difficult to kill. Vampire mythos often cites that to kill a vampire, you must either decapitate it or drive a stake through its heart – those are two surefire ways to ensure a creature capable of regeneration is, in fact, dead.

6. Garlic

A vampire’s aversion to garlic tends to be one of the first fabled traits that modern vampire fiction drops, yet it’s one of the simplest to justify scientifically. It is not uncommon for people who often find themselves handling and cutting fresh garlic to have an allergic reaction to the oils left on their fingertips. Initially presenting itself as a rash, the allergy could become severe enough to mimic the symptoms of a second- or even third-degree burn. In rarer cases, it is not just the garlic’s oil that induces the allergic reaction, but also the garlic dust or vapors, which may be inhaled.

Scientists know that allergies can be passed down genetically, so our homo vampiris can have a genetic predisposition to severe garlic allergy. Curiously, one treatment for a “garlic burn” is UV radiation treatment, which is obviously out of the question for our vampires and all the more reason why they would want to avoid getting close to garlic.

7. Hibernation

The fabled vampire coffin in which these powerful creatures can rest for ages could be justified through hibernation. It is not uncommon in nature for animals to hibernate for up to eight months of the year, and a solid, stone enclosure seems to be a fairly safe place to remain in a more vulnerable state. In fact, disguising this enclosure as a coffin would even keep any curious humans who may stumble upon it from questioning its contents – nature is full of examples of creatures that either camouflage themselves or their nests.

While hibernating, a creature’s metabolic rate can lower by 75%, and its body temperature can drop to below 0 degrees celsius. If some meddling human happens to open that coffin, he can easily mistake the vampire for a corpse in this state – which may give rise to a myth that the homo vampiris is an undead creature…

Why hibernate at all? It is a misconception that animals hibernate in winter simply because it is cold – they hibernate in order to conserve energy when there isn’t enough food available. By hibernating for most of the year, a vampire would allow human population to rebound after an intense feeding period, and maybe even let enough time pass for them to let their guard down or stop wondering who is responsible for those mysterious serial killings…

8. Reproduction

Traditionally, most vampire lore involves vampirism being a condition that can be passed on to any human, either through a bite or other means. This doesn’t match the image we’re constructing, but fortunately, many vampire tales also stipulate that the creatures can reproduce sexually.

Our homo vampiris will be plain ol’ mammals that make babies the good old-fashioned way. Nothing to see here; move along.

The full picture

What we arrive at is an animal that captures most of the elements of traditional vampires, while relegating some of the less plausible elements to human superstition that would have built up around these ferocious creatures. Our homo vampiris is a nocturnal predator and close relative to homo sapiens. It has genetically evolved the strength and sensory capabilities to be a man-hunter, but also has key genetic defects relative to humans. It is a carnivore that feeds preferentially on human blood and, to a lesser degree, flesh due to social pressures. It reaches biological immortality at maturity, mates and reproduces like all other mammals, and spends most of its time hibernating.

And it doesn’t sparkle in sunlight.

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