I have a world build for an Eastern style RPG, which includes the standard trope of monsters being common obstacles the heroes have to battle across the world; though my world gets into detail about where the monsters came from and integrates them a bit more into the actual world and story than many RPGs.

The backstory of the world involves humanity’s first use of magic ending poorly when the magic 'ran out' from overuse, and a side effect of how it was used at the end, when they were desperate to find any way to sustain their spells, was the creation of a sort of magical pollution. This magical pollution acts as a mutagen, mutating human, crops, and animals. In the case of animals, this is what created the monsters of the world.

'Mutated' humans also happened, though far less often than animals (our closer connection to magical energy helped to protect us slightly). Most mutated humans resulted in miscarriage or still birth. A few were born alive but with 'mutations' of some form:

  • most of these mutations being disabling,
  • a few making the human look different but not otherwise disabling them, and
  • a very few rare humans were born (somewhat) stronger then the average humans or otherwise had 'positive' mutations, though not so strong as to make them superhuman or medieval X-men.

This magical pollution dissipated rapidly, and a few generations later the decimated humanity started to recover from the original disaster. By the time of my story the background pollution is still around, but in a much lesser form. Monsters have grown weaker as a result, with stronger monsters generally being in areas where this magical pollution would be more common. However, monsters are still present, and generally have a few 'common' forms in a region. The basic idea had been that the monsters produced at the maximum of the pollution kept breeding and spreading so that they stuck around despite new monsters not usually being born any more; but still feeding off this magical pollution as a source of strength (justifying why decreased pollution tends to weaken them and generally why their energy output is higher than their energy input from hunting should justify).

I realized this was a problem once I threw in humans. I don't want 'mutated' humans to be having children that are similarly mutated. In general I want these magically spawned differences in a human to not pass on to their children. Occasionally a 'mutated' child is still born in present day, but they’re rare and treated as such (varying areas ranging from shunning them as 'evil' to simply treating them as a birth defect to be pitied).

So how can I justify the fact that the monsters are still sticking around, even if weaker than they were when the magical pollution was strongest, but that the effects on humans did not get passed on?

I don't want to fall back on the claim that 'mutated' humans failed to ever have children. Koinophilia would definitely be present, but at some point at least a few of these individuals will find a spouse. Besides, for plot reasons the story works better if these 'mutations' are not generally passed down to children.

  • 4
    $\begingroup$ Animals still live where there is contamination and humans don't if I understand your question correctly? Animals might eat contaminated food while humans do import all their stuff from non-contaminated areas. Animals constantly get mutated again. Why is this not the obvious answer? I also think you should avoid very long questions since they often contain not-needed information. Also, if this is a RPG, you might be overthinking it. Consider not going into biochemistry for this one - many franchises that have many fans never really bothered with consistency, take the Star Trek Holodeck $\endgroup$ – Raditz_35 Aug 14 '17 at 13:50
  • 3
    $\begingroup$ You say, “monsters … kept breeding and spreading … despite new monsters not usually being born any more”. What am I missing? Do you mean “new monsters not usually being born to non-monster parents any more”? Do you mean “new mutations (mutant characteristics) not appearing any more”? $\endgroup$ – Peregrine Rook Aug 14 '17 at 19:04
  • $\begingroup$ Define what your mutations do. Are they just changing appearances (and sometimes affect missing limbs or such) like mutations from nuclear radiation do? Are they permanent? Are there beneficial characteristics that can be utilized from them? $\endgroup$ – Vylix Aug 14 '17 at 21:02
  • $\begingroup$ Perhaps you can change it so that some types of mutated humans have always been around and reproducing -- but now they are full-fledged monsters which aren't very human any more (e.g. think of the creature in the novel/film "The Relic"). $\endgroup$ – John Coleman Aug 15 '17 at 16:56

13 Answers 13


The chance of mutation is increased by eating other mutated plants and animals

The humans in this world are familiar with the mutations, recognize their source, and avoid it as much as possible. While some exposure to the pollution is unavoidable because it simply exists everywhere, it seems unlikely that any mutated crops would be harvested or mutated animals would be commonly hunted for food. Exposure to the pollution is minimized and so is the chance of mutation.

Animals on the other hand are not so discriminating. In fact, many carnivorous animals preferentially hunt prey that are injured or disfigured, and a mutated animal may appear to them to fit the criteria. As a result, animals will ingest the pollution as a major part of their diet rather than just through background exposure; entire ecosystems could exist in otherwise low-pollution areas where pollution stored in the mutants is constantly recycled to make the mutant population much higher than would otherwise be expected.


Related to the idea that the pollution can be absorbed from food, biomagnification could result in carnivorous animals having a much higher chance of mutation than humans even when the ambient pollution has decreased substantially. The concept is that plants and animals low in the food chain absorb toxins in amounts too small to be dangerous, but the animal one step higher in the food chain will eat that animal in large quantities and end up with a more significant concentration. Eventually even a small ambient concentration of the toxin will be extremely harmful to apex predators. Applying this to your situation, humans that eat a mixture of primarily plants and herbivores won't have many steps for this accumulation to occur. Meanwhile ecosystems with longer food chains could have the same background pollution level while having a much higher frequency of mutation among the larger carnivores, and even slight increases in the background pollution level would have disproportionate increases in the mutation rate. A (potentially) desirable side-effect is that wild mutants are typically derived from large and dangerous predators, and in the rare case that the mutation is beneficial these "monsters" could be a major threat.

Finally, if the link of mutated monsters are more likely to produce mutated offspring is key, all the same logic applies except restricted to gestation. In mammals that means the higher pollution levels from their lifestyle is key around pregnancy, and as described above a pregnant mutant animal is more likely to be consuming pollution than a pregnant mutant human, while egg-laying species have the critical period shortly before laying the eggs (though I can't claim any real expertise in what goes into that process). Essentially the link would be that mutant animals are mostly caused by environmental factors that humans intentionally avoid, so if an animal is a mutant it is likely to stay in the same environment and future generations would have the same chances of mutating, while humans actively avoid causing mutations so even if one happens by rare chance their offspring still only has the same rare chance of mutating.

  • $\begingroup$ Bonus for pointing out humans may choose not to propagate a mutation, while animals may not (though, they do have some discriminatory ability). $\endgroup$ – JBH Aug 14 '17 at 18:22
  • 1
    $\begingroup$ Just in the past week a story broke about an animal turning black due to increased heavy metals in their environment. news.nationalgeographic.com/2017/08/… $\endgroup$ – Reed Aug 14 '17 at 20:31
  • $\begingroup$ bioaccumulation $\endgroup$ – isaacg Aug 15 '17 at 13:59
  • $\begingroup$ @isaacg Thank you! According to Wikipedia "Biomagnification" is more specifically what I was looking for, but it does mention that they're often used interchangeably and I likely wouldn't have reached either term on my own. $\endgroup$ – Kamil Drakari Aug 15 '17 at 14:11

I'd say there are two fairly easy ways to 'reduce' the number of mutated humans in a few generations:

  • Magic resistance
    You already said, that humans are less susceptible to mutation than animals due to their connection with magic. This can also mean that animals always pass the mutations to the next generation, whereas humans only do so sometimes (so the number of mutated people becomes less with each generation). This is especially true for 'half-breed' children, with only one parent carrying the mutation.

  • Evolution & social shunning
    If you describe the mutated animals as monsters I'm guessing that they are somehow stronger than normal animals, so they can easily out compete them over a few generations. For humans however, the the mutations don't give any positive effect and it's very likely that mutated people are less likely to find a partner and have children on their own.


We don't go there

The easiest answer is presented by your idea that monsters still happen, but mostly in the areas that are still polluted. Just make the high-pollution areas Forbidden Zones. Maybe this is via political decree or by religious doctrine or just by folklore and hearsay. But people just don't ever go to the bad areas. Or if they do, the monster kill them; problem solved. Or they don't stay long enough to pick up the "mutant powers."

If people stay out of the Dark ForestTM and that's where the monsters come from and that's how people become monsters... Well, that works.

And it also allows for a few outcasts who, for whatever reason, ignore the ban and find themselves becoming the monster. You know, when the plot demands a monster.


Human choice. Get rid of the idea that mutations cannot have children (you already have mutated children); but humans are smarter than animals, and even IRL mutants (people with genetic abnormalities) are usually shunned and very frequently do not reproduce. (I have a grandson with a genetic brain disorder that leaves him about as intelligent as a five year old, for the rest of his life. I do not expect he will ever get married or reproduce or have any children.)

Mutated humans are very unlikely to mate, and you can make the mutations such that TWO mutated humans, combining their mutations, are infertile or tend to have stillborn children. So in humans the mutations just die out.

But animals and monsters with animal levels of intelligence are simply not as picky, not as repulsed, driven far more by scents and sexual compulsions when females are in heat. Males will mate with any female; female animals in heat can be more picky about their partners, but always choose one and mate on a tight schedule; they are biologically compelled to get pregnant within a few weeks.

Mutated humans are shunned as mates. Mutated monsters are not.


Magical Run-Off

Even ordinary, everyday pollution will collect and pool up in various places to the point that people won't go there. Nobody wants to be downstream of the chemical plant. Nastiness tends to get into the water and will pool and eddy, making the surrounding area uninhabitable. It will then stick around for a long, long time. People won't stay in a place like that unless drastic efforts are taken to clean the area up.

Apply this kind of principle to the Magic pollution, but you can have fun with this. Normal liquid physical waste will follow water courses, but make the magic follow ley lines. Have positive and negative nodes that act like peaks and wells in the magical landscape. Now your humans, who created the problem and are now smart enough to avoid it. They will stay away from the Low areas and therefore the mutation rate will go down.

Animals and other creatures aren't going to be as fast to connect the dots as far as the location is concerned. They might linger near the negative node because there is also a natural source of water nearby. Therefore the mutations happen more and last longer.

You can tweak things so that the kinds of node influence the kinds of mutations. a very negative node might produce something that becomes extremely venomous. animals that hang around a positive node grow oversized and really strong, or maybe they gain intelligence.

There is all kinds of fun you can have with this.


Well, you could play it off as similar to Malaria resistance. Perhaps, in the human population, the mutations were genetic breaks that offered some level of resistance to the magical pollution. Then, just as with Malaria, when the environmental pressure is relieved the "pure" Human genome returned to prominence because without the environmental pressure, it's stronger.

  • $\begingroup$ Welcome to WorldBuilding Cale! Interesting first answer. If you have a moment please take the tour and visit the help center to learn more about the site (and earn another badge). Have fun on the site! $\endgroup$ – Secespitus Aug 14 '17 at 20:23

If it was radiation, I would say humans know how to use dosimeters and avoid contaminated areas. Animals don't know any better, and in fact prefer areas humans avoid.

Power of mind could be a factor in the mechanism of the magic, since after all, magic responds to will. Humans could will it into harming them less, and animals would have no idea.

It may operate on a different mechanism. It was originally intended that humans be the masters of the magic, whereas animals and things are under the influence of it.


Animals tend to thrive in places where humans are scarce. They even surprise us by thriving in otherwise toxic environments

It may seem strange that Chernobyl, an area known for the deadliest nuclear accident in history, could become a refuge for all kinds of animals—from moose, deer, beaver, and owls to more exotic species like brown bear, lynx, and wolves—but that is exactly what Shkvyria and some other scientists think has happened. Without people hunting them or ruining their habitat, the thinking goes, wildlife is thriving despite high radiation levels.

Animals seem to adapt to hardships better than people. So the mutated animals still prefer the polluted places, and they prefer them because the humans aren't there. Humans, on the other hand, know full well the dangers and avoid them like the plague. So new mutant animals are still born, and have even adapted to ensuring the mutations, just out of habit.

  • $\begingroup$ Animals usually live too short to get cancer. Animals have strong natural selection -- and they're OK with it. So, as long as they reproduce more then die, they thrive. :) $\endgroup$ – babay Aug 16 '17 at 1:10

You can move some/most changes from genotype to phenotype. Apply those rules (simplified from real world):

  1. Mutations can happen only before conception.
  2. An embryo can't receive a mutations that will affect it, but it can receive mutations in it's reproductive cells that will be inherited.
  3. The offspring receives changes to phenotype being the embryo if mother is exposed to pollution.
  4. Creature does not receives phenotype changes after birth.

That leads to options:

  1. The creature has only mutations. Inherited.
  2. The creature has only phenotype changes. Not inherited.
  3. The creature has mutations and phenotype changes.
  4. The creature has mutations and some special Magic-Adaptation-Mutation. If an embryo with the adaptation receives some magick pollution, it acquires phenotypical enchantments to genetical mutations. The more embryo gets polluted, the more phenotypical enchantments for it's mutations it acquires. So, there are mutations that are inherited, but creature becomes stronger if it was polluted being an embryo.
  5. There might be mutaions that do not show up if not exposed to pollution.

You can have creatures with different options in one world.

Options to reduce amount of mutated people due to magical protection:

  1. Most people get only phenotype changes (only while an embryo).
  2. Most people's mutations are recessive, so child show up it's mutation only if mother and father has that mutation. That leads to people with hidden (not shown up) mutations. If mother and father have same hidden mutation, then a shild has 25% chance to inherit it from both parents. If it happens, the mutation will show up in the child. That might lead to "dirty/blessed blood" screnarios. :)
  3. You can even apply a "Hybrid extinction" option to reduce amount of mutated human. Intruduce incompatible mutation combination, so a child with those combination can't live or can't breed. If humans have too many incompatible combinations, then mutant humans will be able to reproduce only with humans and identical mutants, producing children with hidden mutations.
  • 1
    $\begingroup$ Welcome to WorldBuilding.SE babay! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$ – Secespitus Aug 16 '17 at 7:34

Gestational Contact

Human mutations are not genetic in nature, but are caused by contact with the mutagen during pregnancy. The human innate resistance to magical mutation is developed after the n-th week of pregnancy (insert whatever time scale is useful here), but the mother's resistance doesn't fully protect the baby. As a result, mothers who are exposed to mutagen during certain phases of pregnancy are liable to result in a mutated child. Since this usually results in a stillbirth or miscarriage, the culture has evolved to avoid that kind of contact (think pregnancy and alcohol in modern culture), although it does still happen.

Because the mutations are caused during pregnancy and not genetic, they (mostly) can't be passed down to children. There are a bunch of examples of this kind of thing in our world, including the recent Zika scare.


Willpower. Humans controlled magic. They still have some residual control over the pollution. Less humans are mutated because humans don't want to be mutated.


Wild magic

The magic resists being overtly controlled and overuse leads to a break. The break caused the mutations in humans. The pollution was a different side effect of that same event that embodies the increasing separation between humans and magic.

The wildness of the creatures is actually the reason the pollution affects them. Only the wildest parts of humans can ever interact with that aspect of magic. Some barbarous folks may still mutate, but civilization tends to prevent it.

The urge for order and control conflicts with the nature of this branch of magic.



You also could go for a rather dramatic approach:

Mutated humans where not accepted by society and where hunted down. (similar to the witch-hunt back in 1600th) This even would allow you that there actually still are a few mutated humans, which hide far away. This could be even rather interesting for your story.

A biological or evolutionary reason seems a bit complicated to explain and also is quite boring, imho.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.