Let us imagine later medieval society, very close to our 15 century society. This society struggled with Great Plague. The legends say, that they signed a pact with some supernatural forces, and the Plague vanished. But in exchange, the supernatural forces made every 10th child to become werewolf in later teen years.

Let us assume, that lycanthropy is some sort of disease.

How can I make this disease to be non affected by genetics and gene inheritance?

So, in family that have no werewolfs, there can be a werewolf child. Or 2 werewolves can have normal child.

The werewolf disease is not contagious, or people learned how they could avoid being diseased by werewolves. And the society have developed a means to control lycanthropes - lock them in cellar when moon is full and other means, so they usually do not perform bloodbaths every month.

So, by what looking realistic means can every 10th child become a werewolf?

UPD: some clarification: every 10% of all population are werewolves. I mean everyone who turns 18-20 years can became a werewolf with 10% probability, it does not depend on his/her parents/grandparents/siblings being werewolves.

UPD1: some later clarification that was derived from answers.

0) Werewolfs are real, it is not a delusion. They do not shapeshift or grow fur, tooth and claws, but they are very quick, strong, feral and bloodthirsty. Probably they can be killed by non silver weapons, but there is quite few brave ones that would like to test it. In 99% cases werewolfs are locked in cellars or closets when the full moon is shinning. When the moon is out, werewolves are ordinary people (but probably stronger, healthy, hairy and dog smelling), that can easily coexist with normal ones

1) Lycanthropy tendency can be genetic one, but it manifests with nearly 10% probability, and the current science level in this novel do not allow to predict, if person will be werewolf, or not.

2) This disease was later cured by some mid XIX century scientific approach - antibiotic extracted from fungus for example, or specially processed extracts from wolf blooms.

3) I agree, that it will be more funny to manifest lycanthropy at puberty age, great thanks for mentioning this!

4) It can be some environment agent like wolf blooms to trigger and stop effects and microbial parasites in bloodstream, present in 100% of population, and active in werewolves only.

5) The microbial parasites emerged from some nearly instant mutation of Plague pathogens (yes, it can be magic, but the clear origins of this shift is beyond the scope of story)

So, as i have stated in this update, does this way of events looks realistic?

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    $\begingroup$ I take it we're talking about real werewolves, and not an inherited delusion? $\endgroup$ – HDE 226868 Dec 9 '14 at 21:50
  • $\begingroup$ it is not psychiatric syndrome. Probably they are not fully transformed into wolf, but they become very strong, nearly invincible, feral, uncontrollable and bloodthirsty, like a legendary werewolves. And they can fear silver. $\endgroup$ – vodolaz095 Dec 9 '14 at 21:56
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    $\begingroup$ You can have a genetic condition where parents are not guaranteed to pass on the trait to their children, if there is more than one gene or two alleles involved. For example, ABO blood type. Two AB-type parents can have children with type A, B, or AB blood. One heterozygous A-type parent and one heterozygous B-type parent can have type A, B, AB, or O children. Note that by observing the traits, you can't tell if a person has one or two dominant alleles, so the system wouldn't need to be much more complicated than ABO for a medieval society to be unable to recognize a pattern. $\endgroup$ – KSmarts Dec 9 '14 at 22:29
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    $\begingroup$ Unless the age is very important to your story, I would have the lycanthropy manifest at puberty rather than around age 18-20. It makes more sense physiologically, and gives opportunity for fun (if not especially subtle) metaphors about learning to deal with your changing body. $\endgroup$ – KSmarts Dec 9 '14 at 22:50
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    $\begingroup$ You say that your werewolves "do not shapeshift or grow fur, tooth and claws, but they are very quick, strong, feral and bloodthirsty." So they are not shapeshifters in the ordinary sense (and in the sense used by the [shapeshifter] tag here). Are you sure these aren't fairly ordinary humans who aren't much different other than perhaps having an easier time growing muscle? Throw in a bit of early bullying from kids who feel threatened by their much larger peer, and you could explain the "feral and bloodthirsty" part without resorting to any form of lycanthropy at all. $\endgroup$ – a CVn Dec 10 '14 at 8:18

Start with it being a genetic disease with 100% saturation across the populace. That gets rid of the vector issue. Now the issue is to explain how 90% of the populace do not exhibit symptoms of the disorder. Something must be suppressing the symptoms in almost all of the population and it must be something permanent. Once a person encounters the suppressing agent, they will never again exhibit the lunar transformation but they will still carry the disease and pass it on to their children.

Two additional factors need to be brought into play to truly match your scenario. The disease must be linked to puberty, such that no symptoms ever express themselves until the child reaches their late teens. Similarly, the suppressing agent is only effective prior to puberty; whatever biological mechanism keeps pre-pubescent's from transforming gets made permanent by the suppressing agent, but only while it is present and functioning within the child. Once the hormone storm modifies that biological mechanism, the suppressing agent cannot bring it back or make it functional again.

So what is the suppressing agent? It should be environmental but not linked to any class, career or lifestyle. It should be omnipresent enough that 90% of the populace encounters it in their early years, but there should be no detectable pattern to the 10% who do not encounter it. There are several ways to arrange this...

The suppressing agent could be multi-component. That is to say that two or more agents must be encountered for it to work. Inhaling the pollen of a certain type of tree and then alter drinking water that is tainted with a particular algae. Almost everyone would encounter at least one of the components, but some might not encounter both.

Since the lunar transformations encountered later in life are tightly tied to the phases of the moon, why not make the suppressing agent moon-bound as well. Perhaps a night blooming flower, which only opens at full moon is both a trigger to grown-ups and the suppressing agent for the young. Similar to how the drug, Ritalin has nearly opposite effects when administered to children as to adults, perhaps this flower's pollen is both curse and cure. For those who encounter it early it is a boon. For those who don't, a deadly bane.

Considering that our biochemistry changes with our moods, our sleep-levels and our attitudes, perhaps the suppressing agent is only effective when encountered by children who are hungry, or scared, or tired. Every child experiences each of those states repeatedly throughout their lives, but not every child has been

...hungry on a sleepless night, when the moon is full, when the wolfs-blood flower blooms, and a cold wind cries from the northern hills...

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    $\begingroup$ Problem with such an environmental suppressing agent is that through simple natural selection cultural habits would develop that cause the number of immune people to rise quickly over the course of a couple of generations. (E.g. there is a single village where there is an abudance of those trees and all water is tainted by that algae. Countless of people from that village will claim to have found the cure and sell various (superstitious) random things from their village. One of them is lucky and starts selling the water, greatly increasing the number of non-werewolves) $\endgroup$ – David Mulder Dec 10 '14 at 8:44
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    $\begingroup$ Good point and probably true, but would the lucky snake oil/swamp water salesman know what they've got, given the extended dormancy period. There is no tight feedback loop to allow for rapid, repeated testing of different agents. No analytical tools for determining if a given agent worked, other than waiting for the patient to turn. Even when a treatment worked, was it the treatment or was the patient part of the 90%? I don't think cultural natural selection would unlock this puzzle very quickly. But you are right, it would eventually be unlocked. $\endgroup$ – Henry Taylor Dec 10 '14 at 13:22
  • $\begingroup$ I am well aware they would have no clue at all, they would probably be buying the water and ten other things, all in the hope it will maybe work. That's how medicine has worked for thousands of years and you would be surprised how well it worked. Especially for such a prevalent disease. $\endgroup$ – David Mulder Dec 10 '14 at 14:06
  • $\begingroup$ Just a nit: Puberty is not "late teens" generally, it is more like early-mid teens (individual variances aside). $\endgroup$ – RBarryYoung Dec 10 '14 at 22:53
  • $\begingroup$ True enough, but I stretched it a little to accomodate the question author's desire for a rite-of-passage age first transformation. Personally, I like teenage werewolves, but the author wanted 18yo.'s $\endgroup$ – Henry Taylor Dec 11 '14 at 2:40

The easiest route would be to have lycanthropy function as a normal disease. The following would cause 10% of the population, upon reaching late teens, to become werewolves:

The disease has a high rate of transference; it is airborn, and even those immune to the disease will be carriers. The disease is widespread, and can live in many hosts. The result is that effectively 100% of the population would be in contact with the disease from birth, and thus contract the disease as children. The disease would be almost impossible to avoid; modern medicine may be able to stop it, but in Medieval times, it would be absolutely impossible.

The first symptoms of the disease would seem like a normal baby illness: low fever, general fussiness, but no other obvious effects. In some children, it may not even be noticed. In the course of the illness, 90% of the population develop antigens, which clear out the infection and provide permanent immunity. Those that fight off the disease and become immune will not become werewolves; those that do not become immune after first contracting the disease will remain infected their entire life.

The disease will remain dormant in the 10% of the population that does not develop an immunity, until their body stops producing growth hormones. Apart from those with rare genetic disorders, most people produce growth hormones until their late teens or early twenties. When those without immunity stop production of growth hormones, they will be hit with the second stage of the disease: the disease rapidly modifies DNA, which causes all the effects of a werewolf.

The result is that 10% of the population at any given time will be werewolves. No one knows who will be a werewolf until the first time they change; for the vast majority of werewolves, this will be in the late teens or early twenties. Being a werewolf doesn't preclude your children to be werewolves, not does having immunity protect your children from becoming werewolves.

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    $\begingroup$ Only problem being that the ability to develop antigens would quite definitely have a genetic factor. $\endgroup$ – David Mulder Dec 10 '14 at 8:39

Lycanthropy can be a disease with so long incubation period (20 years) that people cannot see the connection.

For bonus, add some culture: every child need to be recognized/counted by the Guardians every year, during which process they are marked and reinfected. Could be part of standard required schooling. Not having the mark will be capital offense, and consequence will be delayed by decades.

Guardians might not be aware that they are transmitting the disease - they are just performing the rites as required.

Because 90% of the treated will be OK, it will be hard to see the connection. And it might be also infectious, so even non-marked will get the disease if in contact with marked and infected parents/adults, to add the confusion.

To make sure everyone is infected, make lycanthropy protect the carrier from some other, more deadly disease. Say, make non-infected people sterile, so there is darwinian pressure to get infected, and pay the price.

Key is long incubation period. Any benefit, like protecting from other disease, is just frosting on the cake.

  • $\begingroup$ "Any benefit, like protecting from other disease, is just frosting on the cake" - brillian idea! $\endgroup$ – vodolaz095 Dec 10 '14 at 17:38

If a curse is like a disease then yes it is possible that not all individual in the population will develop it. Population here simply refer to a group of people. Actually, 10% of the population is a lot of people. Some diseases are present in the gene of an entire population is because the gene is present in the population. people might develop symptoms or not. Some develop more severe symptoms than others.

Non genetic transmission :

Environment: The disease can be present in the environment but people are unaware of it. At the time, medicine was less advance than it is today and they have no idea of what is going on. The diseases affects some people, other are immune or show only minor symptoms. Some might also catch it but without developing any symptoms.

Cultural: Yes this seems strange. but I was thinking how Ebola was transmitted. During the funeral rite, in these African countries, they need to clean to body. But by doing so, they are spreading Ebola because the hygiene is too rudimentary. I guess we could image something like that since you mentioned that it happens at a specific age. People need to do something that exposed them to the disease without knowing it. It could be eating something, going somewhere or some sort of blood ritual. The last one in particular is a good way to get into trouble with or without lycantropy.

  • $\begingroup$ Environment transmission looks very probably to me, we can assume that origin of this lycantropy is microbial scale parasitic organisms, that exists in environment, but are triggered by mysterious means to every 10th teen. $\endgroup$ – vodolaz095 Dec 9 '14 at 22:49
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    $\begingroup$ @vodolaz095 By 10% I understood you were talking about probabilities meaning that if you take a sample of 20 people, it's possible to have no werewolf but on a large population of say 20 000, your likely to have 10% of infected. But it's not possible using probabilities to predict at 100% that the next person will become a werewolf. $\endgroup$ – Vincent Dec 9 '14 at 23:29

Your description actually reminded me of genetic resistance to malaria and sickle-cell anemia. (It's actually very fascinating.)

I think you may be able to drag and drop from that wikipedia article to your problem case. Just like some of the people who are naturally immune to malaria also become sick with sickle cell anemia, some of the people who survive your plague are going to be susceptible to this lycanthropic condition, whatever triggers it. (Perhaps something environmental, like a mold that most people don't even notice.) As a plot twist, you could even reveal at some point that there really wasn't any supernatural intervention, the demons who claimed to do it were just swindlers, and drama ensues!


If a disease is not contagious, and it's not genetic, there is no vector for transmission for the disease and it will die out. You need at least one of these vectors to be active.

Genetically, lycanthropy could exist as a homozygous recessive trait that will only show up when both parents have one gene for it. Only individuals with two copies of the werewolf gene would exhibit lycanthropy, so the parents would posses the gene, but not be werewolves. A homozygous recessive trait would also mean that any child of two werewolves would always be a werewolf. It's also that it's a more complex genetic disorder, which is triggered by some environmental factor. Lupus is a disease that follows that pattern.

As a communicable disease, you can have transmission at a young age, but only in low numbers, or have a disease that's generally asymptomatic in the population, but which everyone, or almost everyone, has.

Of course, there's also no real-world mechanism for making someone undergo significant physiological change under a full moon or become nearly invincible, so you might need to use at least a little bit of magic to actually make werewolves work.

  • $\begingroup$ It could also exist as a genetic trait with more than two alleles, which could fix the problem of werewolves always having werewolf children. A genetic condition with an environmental trigger would also work to conceal the source, but remember that this is roughly 15th-century, and Mendel didn't come along until the 19th. A moderately complex genotype would be effectively unpredictable. $\endgroup$ – KSmarts Dec 9 '14 at 22:35
  • $\begingroup$ i agree, that it can be genetic disease (i'm not very good at genetics), but it have to manifest nearly randomly on every 10th child $\endgroup$ – vodolaz095 Dec 9 '14 at 23:29

I'm thinking of MS. They still don't know what causes it. It affects one in every 800 in the UK, something like. All they know is, there is a genetic part - siblings tend to get it too, but children of sufferers are less likely to have it than siblings (I suppose they have less DNA in common than siblings). People with Scottish - Nordic ancestry are more prone to getting it. Some people claim it is triggered by a childhood disease such as mumps, or a vaccine, or some environmental substance. Nobody knows, though many people are working on it.

BUT here's the weird part. If people from the same genetic group are brought up in a warmer place, nearer the equator, until they are about 13 (so, puberty), they are less likely to get it. No-one knows why.

Here's a link http://en.wikipedia.org/wiki/Multiple_sclerosis


I think the 10% figure would not be stable over time or location. If alleals give resistance to one thing but cause problems, the population will strike a ballance that will shift with the balancing factors.

Age onset: I know that puberty is easier, but let me point out that many mental illnesses start showing at early 20's. A friend of mine from high school developed bipolarism after leaving for college; the Beautiful Mind movie showed his schizophrenia upon arriving at university.

Something like that (psychological effects) could also trigger linked physical effects caused by hormones controlled by the brain, as with flight-or-fight response.


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