# How to limit the proportion of a Force sensitive population?

I'm making a world where small part of population are like Star Wars Force sensitives. They have high status in my world, as the sensitivity gives them certain advantages over ordinary people. A trained sensitive could defeat several Special Forces type of soldiers, though a dozen would probably kill him.

Sensitives are over-represented among the top of the society. To be born sensitive grants you a chance to become part of the elite. Having a sensitive among your family, friends & neighbors is an enormous prestige. It's the same as with aristocracy two century ago and movie/sport stars now.

A child born of two sensitives has a much larger chance of being a sensitive, than a child of two ordinary citizens, though sensitivity is an exception not a rule. Most children born to sensitive parents are not sensitive themselves, and sometimes a strong sensitive is born to normal parents.

Sensitivity is a weakly heritable trait.

The country runs an extensive system for finding and identifying sensitive individuals, regardless of their class. Every sensitive must be trained, whether they or their parents like it or not. Those who run away are considered fugitives, those who help them are considered traitors. On one hand an ordinary family could quickly rise in status for having sensitive child or even better several of them, on the other hand once preeminent families wither away for failing to do so.

The problem I face is that I want to limit the number of sensitives to a small part of the population, something like 1 in 10,000 would suffice.

The question is: How to reconcile small numbers of sensitives with sensitivity being a hereditary trait?

The ideas that don't work in my settings are below:

1. High mortality rate, due to wars & infighting. However female sensitives don't usually go to war, unless there is an emergency. Therefore they could simply repopulate the pool.

2. Caste system where noble bloodlines keep the right genes among themselves. The problem is that sensitivity is a badly needed trait for the society. The country wants to have more sensitives as they are very handy in wars with their neighbors. Being the ruling caste doesn't mean anything if your country is destroyed. The society doesn't care if your father is Michael Phelps or Joe Schmo, you could either swim fast or you don't. If you have potential you must join, it's not a destiny you could choose.

3. Reduced fertility. For women this might work, but the problem are men who could sire hundreds of children every year. Besides even among sensitive couples the chance to have a sensitive children is low. They might have one or none. This is an important part of my story, with preeminent families falling from grace, when they are unable to produce sensitive offspring. Similar to how a family could be devastated in ancient China when it was unable to have a member that passed imperial exam and become a government official.

• Hello @saren and welcome to Worldbuilding. At present it is a little bit hard to figure out what your actual question is. Here is what I normally recommend; structure a question in the form: premise, problem, query. Ok, you have a premise, this is all fine and well. But what is the actual problem that you are facing? What is it that has gotten your stuck in your creative process? Please define this. And once you have defined the problem, make the query: the who/what/when/where/how question that — if answered — solves your problem. Click "edit" and try this, all right? :) – MichaelK Mar 20 '17 at 11:04
• Well the thing is: you have essentially answered your own question. There you have not just one but three workable solutions to your problem. :) – MichaelK Mar 20 '17 at 12:57
• Weakness to disease for all the sensitives? It's a common thing in nature. People of African descent have a weakness to sickle cell disease but lower mortality in the first 6 months of their life. – Mormacil Mar 20 '17 at 13:44
• @Saran: You'd need to reduce it to a lot less than that! While siring hundreds might be theoretically possible, it's wildly unlikely in practice. In fact, if you look at historically nobilities, they typically have relatively few recognised children and probably a number of illegitimate offspring. Meanwhile, deaths in battle are rare among the nobility, they have the best armour, the best weapons, the best mounts, and guards to protect them if they fall. – Jack Aidley Mar 20 '17 at 14:30
• This question is being discussed on meta: worldbuilding.meta.stackexchange.com/q/4719/28 – Monica Cellio Mar 21 '17 at 3:17

Since sensitivity is somewhat heritable, how to prevent it to spread among the general population I want sensitives to be rare something like 1 in 10,000.

Being blonde is heritable. You have much more probabilities of being blonde if both your parents are blonde, but there's a small chance a blonde boy or girl is born out of non-blonde parents.

You don't have to do anything about it. It's just how genetics works. In fact, you do want it to be spread among the general population, otherwise the probability of a sensitive being born in the general population would be zero. The genes carrying the sensitiveness to the force are "in the wild", but they are recessive, say something like 1 in 10,000 births - but way more probable if both parents have these gene active.

Evolution's ways are twisted and intertwined. In theory, any change that is beneficial for a species should grant a reproductive advantage and so, it's more probable its offspring would survive while other individuals' offspring dies until this beneficial trait becomes commonplace. However, that only works when there's a huge pressure on survivability of said species.

For instance, let's look a giraffes. Long, long time ago, giraffes had a neck like horses or zebras. Some of them had a longer neck, some of them had a shorter neck, but it wasn't an advantage per se. Then, some kind of global crisis happened (a glaciation, a change in the rain patterns, whatever...) and then all the food was gone and 99% of giraffes died (short and long neck). There was little to no grass at all, but giraffes can eat leaves, too, so they resorted to them, but very soon all the lower-hanging leaves were gone, too. And then, only then, having a longer neck became an advantage important enough so to 99.9% of short-neck giraffes died while "only" 99.1% of long-neck giraffes died. The survivors were nearly all long-neck giraffes and their offspring were even longer-neck ones. In just a few dozen generations, horse-like giraffes have turned in today's giraffes.

Without that kind of pressure, though, evolution is much more subtle or even maybe stalls - we don't know for sure. In our world, being filthy rich is an obvious advantage but rich people don't have more children than poor people (on the contrary, I would say). Unless you design a world where the non-sensitive humans are doomed to go extinct due an external cause, I don't think natural evolution would make this trait universal.

Now, if we are talking about selective breeding, that's entirely a different question...

• This works for me but wouldn't amount of sensitives grow over time, if the trait is very useful? – Saren Mar 20 '17 at 12:52
• @Saren Don't accept an answer so early. Give it a day or two and you might get more and better responses. People are less likely to look at questions with accepted answers. – kingledion Mar 20 '17 at 13:04
• Your answer seems the best , though I think that proportion of sensitives would grow over time. However if the growth is very very slow nobody would notice, and events like being forced to send woman sensitive into battle where they could die, could kill that growth and keep the percentage in check. Will wait a day if something better doesn't appear I will accept your answer – Saren Mar 20 '17 at 13:04
• @Saren With evolution "useful" means "increased chance of having children who live until fertile age". Even with "force" being valued by society it isn't necessarily associated with having more children unless something like polygamy for sensitives is enforced. It is actually reasonable for the sensitives to have less opportunities and time for having family. – Ville Niemi Mar 21 '17 at 8:38
• @Saren: You say you feel that the proportion of sensitives would grow over time. It won't. e.g. Even if you start with a population that consists entirely of sensitives, the second generation will already have much fewer sensitives than the first gen; and so the third generation will have even fewer sensitives, until finally, the percentage of sensitives will reach a steady state. Variables such as the percentage of sensitives who will prefer other sensitives as sexual partners, and whether male sensitives will be in demand among women will only boost the steady state somewhat. – ArjunShankar Mar 21 '17 at 17:08

You can borrow an idea from Flatland, and enforce a reduced fertility as consequence of this force.

Force bearing individual will have lower chance of being fertile, this reducing the amount of newborn potentially bearing the same feature.

• Flatlandia? Isn't that the book/animation about higher dimensions? – Mormacil Mar 20 '17 at 11:27
• @Mormacil, yes. and the circular classes there are fertility limited – L.Dutch Mar 20 '17 at 12:02
• I believe the English edition is called "Flatland" – NonlinearFruit Mar 20 '17 at 19:05
• @NonlinearFruit, you are right, my bad. Fixed. – L.Dutch Mar 20 '17 at 19:47

There are many ways to do this so the following are broad catagories:

1. Biological Reason for Low Incidence Rate: There is some genetic detail of the force so that can't be easily passed on. Maybe sensitivity is a non-inheritable genetic mutation. Maybe it requires an additional chromosome similar to a favorable down syndrome or Turners. Maybe a mother, especially one who is not force sensitive, will be damaged by a force sensitive fetus resulting in a miscarriage or maternal death. There are many ideas for this, some interesting and some limiting storywise.
2. Lack of Reproduction Among Upper Class: I don't think this takes much explanation as it is a real phenomenon. Rich families often produce fewer children than individuals with less wealth. Explain this in your world, however, you like: they don't want to sacrifice their me time raising them; private schooling (force training) is expensive; too busy working since they have the hard ruling party jobs; their religion dissuades attachment or sex. This won't help a specific noble family, however, unless they wait too long to start trying.
3. Culling: It is dark but good for story. Someone seeks out and kills younglings. Maybe it is a secret organization. Maybe it is public knowledge. Be creative as to why. Maybe they aren't killed but kidnapped...how is that for a story?
4. Other Removal from Gene Pool: Force users are likely to become infertal (or specifically unable to bring force sensitive children to sexual maturity). This would be best if it has nothing to do with the force but is a result of inbreeding to try and produce force sensitive children.
5. Accidental Self Injury: Force users can do amazing things but they don't realize the downside. Some force sensitive children experience SIDS as they use their powers without control on themselves as infants. Older ones playing with their abilities don't know how limited their self control is...until it is too late. Maybe all of them incur some degree of physical damage to their body through the use of their powers and that leads to chronic illness or acute fatal symptoms a fraction of the time.
6. Asymmetric Heritage: This is different from 1 but similar. Midoclorians (I don't care enough to check spelling) are inspired by mitochondria. These are passed on only from mother to child. Maybe only the mother can pass on the force so the father's procreation rate doesn't matter. Not knowing this, the matriarch of the family is the result of adultery/secret adoption and, as they bring in force sensitive male suitors, nothing helps. The remaining force sensitive men obviously can't do anything, as much as they get to try, unless they mate with the force sensitive woman who can't just be paid to act as livestock for breeding.

My current favorite is number 5.

Here are some possibilities. They each work for very specific "worlds":

Force use is not genetic. There are "force spirits" that are born into people. The number if force spirits are either fixed or grow at a specific rate.

Force use requires more than one gene change to produce results. It takes a specific combination of these genes to produce a force user. Also, if the combinations isn't just right it results in a terminal mutation. That would make force uses appear to be randomly generated because any time you had a population with almost the right set of genes, most of them would miscarry.

Most babies that can use the force die from it. Maybe the fetus reads too many minds and dies from shock, maybe it tries TK (as it kicks and moves arms) and causes cellular damage while still in the womb. This would result in only the force users who are too weak to manifest on their own surviving.

Personally, I favor the second option.

• This is like the Chinese Crested dog breed and the hairless gene, the hairless gene is dominant but an embryo with 2 hairless genes is non-viable, so it's not possible to have "pure" hairless dog, as such a mating of two hairless dogs can always produce some hairy offspring. – Blake Walsh Mar 21 '17 at 22:40
• @BlakeWalsh, That's really good. I hadn't thought of that angle in my answer. You should expand that into a full answer. – ShadoCat Mar 21 '17 at 23:37
• @BlakeWalsh Sickle Cell works the same way in people. It's actually mildly beneficial to have the trait recessively in (I think) malaria prone regions but it's close to fatal to have two copies of sickle cell gene. – Mathily Mar 28 '17 at 21:25
• @Mathily, yes. With one gene, malaria causes the red blood cell to deform and be removed from your system. With two copies of the gene, red blood cells deform spontaneously and can clog arteries causing strokes and heart attacks. – ShadoCat Mar 28 '17 at 21:54

You are thinking this about right.

1. Untrained sensitivity - in low parts of the society no one would know you are / can be sensitive. Without training it wouldn't be an advantage, so no evolutionary pressure for this trait. This would mean that this trait may reasonably be expected to spread or not, just like other minor traits, like different eye colors. If it's not helping you to survive or procreate, it's moot, evolutionary.

• This opens up a place for dark cults, hidden shrines, rogue teachers and similar plot hooks.
• Emergency testing and teaching to get an army, at the cost of social crisis.
2. Untrained who can use it anyway would be danger to himself. So you can push someone, hard. But if you don't know how to stabilize your own body at the same time, you're breaking your spine. You can jump 5 meters high, but you don't know how to land. and so on. If you are dead or severely injured, you don't procreate, and this would make force sensitivity a trait purged out of low class people, it evolution is allowed to work.

3. Taking talented children into higher caste and leaving their families behind. Just like Anakin was taken to life in luxury and his mother left to die as a slave and no one seemed to be disturbed. This would leave no sensitive parents in the social classes you don't want to have many sensitive children.

This works well for force users, magic users, psi users, X-Men style mutants in caste society, and so on.

• I don't see how this answers the question. – kingledion Mar 20 '17 at 13:05
• @kingledion Why? all points shows reasons why there wouldn't be many force users in low castes. Being unable to use it without training, killing yourself if using without training, and being removed from low caste if you are force user all causes low percentage of users in low class, aren't they? – Mołot Mar 20 '17 at 13:11
• I'm just saying, if I can't see how you are answering the question, other people might not either. In that case, maybe edit your question to be more clear. I don't think you are connecting the dots between the three things you mention, and the reasons why that would limit the population. – kingledion Mar 20 '17 at 15:30
• Most people wouldn't say Anakin was taken to a life of luxury, what with the strict asceticism and stoicism the Jedi Order demands. Not to mention the way Jedi must constantly risk their life and cannot retire. Though yes forcing the force-sensitives into a life of chastity like the Jedi would limit their numbers. – EldritchWarlord Mar 20 '17 at 15:42
• There's an extensive system in place for recruiting sensitive children regardless of their birth. If Anakin was born in my world he would be quickly found and put into training while his mother would become upstanding citizen and live a life in luxury. Watto would not have any say in this. The state would compensate him for his slaves, for whatever value it seems fair, something like eminent domain in our world. – Saren Mar 20 '17 at 15:56

Magic has its own rules

The Force is magic. You're going to be breaking the laws of scientific reality all over the place in order to have the Force at all, so why do you feel the need to tie the inheritance of your magic to genetics? Just have it behave how you want it to behave, it doesn't need explaining and it is highly unlikely that trying to tie it to a genetic cause will make it more satisfying.

If the force is a field that force users are sensitive to, the number of people who are trained to manipulate it will cause a gratuitous amount of noise in 'the force' thus reducing the effectiveness of any one 'force user'.

This would mean that it is in the best interest of the top of society, who are force sensitive and politically powerful, to limit the number of other people trained to effectively use the force in order to maximise their own power.

This could potentially take the form of an oppressive dictatorship that ruthlessly crushes all other potential force sensitives, ensuring one or two force users remain supreme, or perhaps a quasi-religious military organisation that indoctrinates potential force users into a strict 'use only when necessary' policy.

• Very interesting idea though I don't feel that it fits well with rest of my setting. – Saren Mar 20 '17 at 12:59

Since the "Force" is already a mystic element, you can simply combine a mystic element with the inheritable trait.

The Force is a pool of energy. This energy is naturally generated by sentient life though rapidly disperses into the universe at large resulting in this energy being distributed relatively uniformly.

The rough likelihood of a latent Force Sensitive person being able to manipulate this energy is proportionally related to the overall sentient population and inversely proportional (with a much stronger weighting) to the total population of active Force Users. This results in a rough ratio of 1 Force User per 10,000 sentient beings.

A child of one or more Force Users (should the child be Force Sensitive), has a small (though not insignificant) increase in the likelihood of becoming a full fledged Force User. Children, in general (should they be Force Sensitive) are significantly more likely than an older Force Sensitive to develop into a Force User, should a "slot" become available. It is not unheard of for older people to spontaneously developing into Force Users, but it is rare.

Note that should a large number of Force Users be killed, this method of generation will result in a similar number of Force Users swiftly developing, though a majority of them will likely be children and youth.

You might treat sensitivity like a theory concerning autism. Make it require both a genetic disposition coupled with some sort of external stimuli. You can adjust the incidence by making the external stimuli to a greater or lesser degree known and possibly harmful. For Example, once genetic disposition is determined, the mother must take some sort of catalyst that has a 70% chance of being fatal to the child, but only a 10% chance of triggering the change that would cause sensitivity.

As an alternate method, make the genetic disposition a typical genetic regressive trait, but levels of sensitivity vary greatly. You might have 1 in 4 with a genetic marker for sensitivity, but only one in a 1000 has a worthwhile level of talent. The ones with a useful level of talent are the ones sought out, and you might have a pseudo underclass of those who didn't quite make the cut.

Either way, genetics is complicated enough to support your basis for a sensitive meritocracy. You can look at History, and in spite of the nobilities attempts at breeding, you only ended up with a good king every once in a while. The Empires of Alexander the Great and Genghis Kahn only survived until their deaths and fell apart during the next generation.

Reduced fertility. For woman this might work, but the problem are men who could sire hundreds of children every year. Besides even among sensitive couples the chance to have a sensitive children is low.

You could posit that one factor that increases the chances of a Force-sensitive child to be born, rather than a normal one, is Force attunement between the parents. Which is more likely to grow with time and acquaintance. Without that, the genes are there, but the power doesn't awaken sufficiently.

After several centuries of experimentation, it has then been found that to maximize the chances of an ESP birth, both parents would need to enter seclusion together for several months before conception and remain there for two or three months after the birth. At the very least they must avoid any intimacy with other ESP-endowed people, and to be more sure (anyone might have a slight attunement to the Force, and slightly decrease your attunement with your partner), with anyone else.

When scrupulously following this regime, the chances of a Force birth increase from very little to perhaps one in ten.

This has the possibly interesting side effect that people with no attunement whatsoever and as little Force genes as possible would be highly requested for the role of servants, as they would bring the minimal disruption to a secluded household.

Another side effect is that a family - unless large enough - would have to choose between delving into high caste politics, and interacting daily with the Court, or have its fertile members secluded to churn out more children, thus losing influence.

To cull the noble offspring, consider that a half-Forced boy or girl hasn't all that great a future to look at; so the temptation might exist to try and awaken the Force with some dangerous ordeal, with a ten percent chance of awakening the Force, and a fifty percent chance of ending up dead (I half-remember something of this kind in MZB's Darkover series - some dangerous way of awakening one's laran. I might misremember, though).

# The world is not static.

Right "now", there is only 1 in 10000 Force Sensitive (FS), but it wasn't always so. And it will not always stay so.

One possibility is that FS is a recent development, and ten thousand years ago there were none. Then somebody got lucky in the genetic/environmental lottery and the first Jedi was. They had more children than average, and those children had more children than average and so on, but it still a rare trait. In the future it will be more common.

The other possibility is that they used to be more common, but for some reason most of them died. Maybe they were killed as witches, maybe they lost a civil war. Again, they will be more common in the future... unless there is a new witch hunt.

(The above is my unique contribution, below I repeat points made by others to make this a complete answer)

# Weak inheritance

You said that FS parents had an increased but still low probability of getting FS children. This can be achieved in two ways.

The first is making the genetic basis very complex. Maybe you need one of two genes from group A, one of three from group B as well as one particular gene C. All of these genes are somewhat rare. Parents are likely to not carry more genes than needed, and can fail to pass them along in several ways. People having more than the minimum number of genes can be stronger FS, but not dramatically so.

The other way is to make the genes only part of the equation. Having the right genes only gives you a chance, in addition you must get some boost from the environment. Maybe during pregnancy, maybe early childhood. E.g. a near death experience can "wake you up".

Note that either way, weak inheritance will make evolution move even slower, making my first point more valid.

# Who cares anyway.

The world is as it is, and the people in the story doesn't know why. The readers doesn't need to know why either. Nor does the writer.

A Caste system, probably religious in origin. Sensitive children are forced into service. Perhaps the only way out is marrying into a noble family.

Another way is to make the sensitivity come from a mutation first found among the nobility or even royal bloodlines. They simply kept it among themselves by inbreeding. You could even again use a caste system and reproducing with a lower caste is a sin for the sensitives.

You could have some hidden romances throughout the ages that allow you for some very rare sensitives among the lower castes. Still caste breeding can be a very rigid system. It was very effective in India. We can still see the effects of caste divides in DNA these days. There was just that little contact between castes.

For population reduction I'd go with a wasting disease that specifically targets sensitives or at least affects them much stronger. Perhaps regular people would only be carriers. This again could force a societal divide between the sensitives and the rest.

• I have something similar, sensitive woman are limited to marrying only sensitive men to increase the chance of having sensitive offspring. But castes do not exist, it doesn't matter if your father is Michael Jordan/Lebron James, you could score 25PPG or you can't. – Saren Mar 20 '17 at 12:57

You ask specifically about genetic inheritance. This means that a lot of the suggestions about alternative explanations are incorrect, especially the handwavium of "it's magic".

If it is a simple hereditary trait, then it would end up a lot more common. Thus it is more likely for the Sensitivity to be a genetically complex trait, perhaps even bound to the specific sex chromosomes (making especially men (Y chromosome) or especially women (X chromosome) to be more likely to be Sensitive).

Another way to look at it is by making Sensitivity be a sliding scale, like intelligence. To simplify, you could say everyone has 20 genes in their DNA structure that might or might not influence Sensitivity. If the gene has the Sensitive variant, the person becomes more Sensitive. On low levels this translate to good intuition, luck, athletic ability, etc. It all depends on which specific Sensitive genes are active for that person. To be actually Force Sensitive to a level that it can be trained, you would need to have 60% of these Sensitive genes activated. More activation, of course, results in a stronger Gift in the Force.

But alas, the problem then comes for the family. Even if both parents have a large amount of active genes, these are recessive and unless both have the same ones, this will not inherit all the time. But their children will still be gifted above average, even if they are not actually Force Sensitives. At the same time, with all these genes flowing through the population, giving ever so slight advantages to people here and there.. it remains active and wanted within the population. Often people with similar genes come together due to similar interests and talents. And chances of their children having enough activation to count as Sensitive increases with each generation as like seeks like, without this becoming an actual certainty.

We can then look at simple statistics and chance. If the amount of genes decide the chance of the child being Force Sensitive, then in the limited pool of FS people, it is noticeable not enough to get consistent results. Unless perhaps the exact genes are known and a breeding program is started. In the general population a chance of 0.001% is not much, but if you have a million babies born to people with the latent genes.. then 0.001% is still going to be a fair amount of Sensitive babies (0.001% of 1 million = 10).

Finally, besides the presence of genes, there is also the activation of genes. If the genes never activate due to environmental influences, then one can have 100% Sensitive genes, yet not display any of it due to the genes being dormant because the body did not perceive a reason to activate these genes yet. Viruses interact with genetic activation, and could be a cause why the richer families are not specifically more successful in getting Sensitives.

## Make Force sensitivity a partially inherited trait, and give complete inheritance of the same genes a downside

Over the course of evolution, purely beneficial traits tend to become more common in a population. Rare traits are sometimes controlled by multiple alleles where partial inheritance is beneficial but complete inheritance is detrimental, thereby ensuring that the trait remains rare but does not disappear.

Maybe partial inheritance of Force sensitivity genes gives special powers, but complete inheritance of the same genes has a high chance of causing insanity due to too many psychic voices. Perhaps full inheritors tend to die in utero, effectively reducing the fertility rates of inbred families of sensitives. It doesn't have to be strictly single-gene Mendelian inheritance, but rather a higher chance of detrimental traits that increases over multiple generations of sensitive inbreeding. This will ensure that the genes remain "spread out" among the population and you don't wind up with "noble" families that keep all of the special genes for themselves. (Or there might be some families that do, but they will tend to have problems.)

So you need to be trained as well as having the natural ability. You could make it so people with the ability (without the training) don't even realise they can do it. In fact, special techniques and equipment which are tightly controlled are needed to detect force users.

That way, the elite can enforce a whatever number of users they like.

• You could even adopt the idea of a "critical window" for learning, so training must begin when the children are very young to work. – Jack Aidley Mar 20 '17 at 15:49
• This is counter to what the question is asking. The elite do don't want to limit or enforce the numbers, as I read it. They want to have as many as possible. I read question to ask: So what principle or situation can balance this? – Loduwijk Mar 20 '17 at 17:20

I would suggest the combination of one and two. As you said in times of great conflict force-sensitive females can also be drafted into the army. Just great series of large conflicts. ( like World War 1 and World War 2 scale). That Force the nations of the world to put every force-sensitive available on the front lines.

Combine this with the fact that the force sensitive is ownership of land and wealth and your force-sensitives have an incentive to keep the force sensitive population low. The more force-sensitives there are the more land and Wells needs to be distributed among them the less one has. This is why the nobility what often disinherit all but the first born is if they divided the lines equally then each generation would have less.

• Two doesn't work because families have no incentives to limit number of sensitives. If Johnson's have 4 sensitive sons and they are strong/cunning/lucky/etc to survive the training, war & internal politics they would have 4 bread-winners. On the other hand if Smith's have only 1 he could be weak/foolish/unlucky/etc to die and they would lose their stipends & privileges. Johnson's would get 4 palaces while Smith's would get an apartment as a consolatory reward. – Saren Mar 20 '17 at 13:52
• @Saren yes they do a nobility Is wealth is not dependent on his Force Sensibility dependent on his status as a nobleman and the land and privileges that comes with. That status is the deturmened Sensibility it doesn't even have to be a good Force user. So there's no reason for a family to have more then one or two Force users. Noble man's don't work for money they receive taxes, they're not Breadwinners – Bryan McClure Mar 20 '17 at 15:05
• It seems my nobility comparison doesn't fit. Having powerful sensitives in your family increases your status. The more of them you have in your pedigree, the closer they are to you and stronger they are, the greater positive effect on your status. To compare them with dogs it looks for working lines not show lines. The sensitive have status by how they perform not by who their great-grandparent is. Oscar Robertson being your grand uncle is nice, being first cousin of Curry, Durant & James is much better. Even if you don't play basketball people will assume you have it in your blood. – Saren Mar 20 '17 at 15:32

Because the gene combination that activates those powers is all recessive. It's why the upper castes inbreed to improve their chances of having force sensitive children-- which in turn leads to all the other problems of inbreeding, resulting in higher mortality and deformity.

• Recessive genes are, almost always, broken genes. Non-functional variants of genes where the dominant form is able to produce function at reduced dosage. It seems extremely unlike that "force sensitivity" could be the result of a broken gene. In fact, the idea of "force sensitivity" as any single gene seems pretty far fetched. Furthermore, inbreeding has to be really very extreme to produce large changes in mortality, and since force sensitivity is such a positive trait it seems unlikely it could overwhelm it. – Jack Aidley Mar 20 '17 at 15:47
• @JackAidley: Note the word "combination". Imagine a dozen allele pairs, where it's nearly impossible for all of them to be recessive, and the dominant form doesn't really do much. You'd expect that the recessive (r-r) form should do nothing either, except the combination of those specific r-r pairs unlocks (literally) force abilities, where even one D-r out of the twelve pairs would not. One might even combine this with other recessive traits, e.g., only redheads can use the force. – nzaman Mar 20 '17 at 18:20
• In your case, the children of two force-sensitives (i.e. two persons with only recessive alleles) would automatically also have only recessive alleles, i.e. also be force-sensitive. (In the original example of mendel, wrinkled peas only produce wrinkled peas.) Which is not what is wanted in the OP. I would more think of a combination of multiple genes, where most of them are dominant, but with some fertility reducing side-effects so they become rare. – Paŭlo Ebermann Mar 20 '17 at 23:14

Nothing. Your rules already allow for a limit proportion of force-sensitive population, as long as your numbers are right. Kind of.

Proposition 1 : If the number of special children born of each special parent is less than 0.5, then the majority of special children will be born to non-special parents in an equilibrium situation.

Proof: Since we have an equilibrium situation, the number of special people $S$ must remain the same from one generation to the next. However, if the number of special children born of each special parent is less than 0.5, then there are less than $0.5S$ special children born of special parents. The rest must thus come from normal parents.

Proposition 2: If we let the number of special children born of each special parent be $s_s<1$, the number of special children born of each normal parent be $s_n$, and the ratio of special people all people be $S$, then in equilibrium situation,

\begin{align} S = s_s\cdot S + s_n(1-S) \end{align}

This proposition just states that the population of special people is a constant over a generation. In other words, the number of special people is equal to the number of special children born from special parents plus the number of special people born from normal parents.

Now, if $S<< 1$, we have roughly

\begin{align} S &= s_s\cdot S + s_n\\ s_n &= S - s_s \cdot S\\ & = S(1-s_s) \end{align}

So, what does this mean? Well, it means if we want the ratio of special people to be $0.0001$, and we want each special parent to have 0.5 special children, then each normal parent must have $0.0001\cdot (1-0.5) = 0.00005$ special children.

So, let us set up a scenario where that happens.

Example

Consider 2 special people who have children. Since they are of the elite class, maybe they will have a lot of children. Let us say, on average, they have 5 children. Our number tells us that 2 special people should have 1 special children. So the chance that a child is special, given that both parents are special is $20\%$.

Consider 2 normal people who have children. Perhaps they only have 2 children, since they are not elite. On average, 2 normal people should have $0.0001$ special children. So the chance that a specific child of theirs is special is $0.00005$.

Finally, let us consider a special parent with a normal parent. Let us say they have 4 children on average. They should have roughly $0.5$ special children. So each child has a $12.5\%$ chance of being special.

This example, of course, might not fit the genetic model. However, you can change these numbers a bit to fit the genetic model, and ensure that each special parent has 0.5 special children on average, and each normal parent has 0.00005 special children on average.

This is inspired by Stig Hemmer's answer:

It isn't just genetic

Even if the society had technology at our level, they wouldn't necessarily know who would have the force. There are aspects of gene regulation that are influenced by a myriad of environmental factors, and not just the presence of some genes in your DNA. Things like DNA methylation and the necessity of trace elements/vitamins as well as the randomness inherent in the development of everyone's brain means there is a lot of post birth randomness to play with.

Think of it like intelligence, it seems to be at least sort of heritable, but the much bigger impacts are environmental. Maybe the force is like being an outstanding genius. We could all learn to use the force a tiny bit, most of us top out at being able to move something that weighs an ounce, but there are a few of us who are profoundly gifted.

Those who show the gift (like musical prodigies) are identified easily at a young age a shepherded into training programs to refine and build on their talent. Like music (and the force) it requires a great deal of training to build on the raw talent we identify in the occasional youth to create an adult who has real power.

This would create a situation where there would probably be a lot of middlingly powerful people who might be able to pick up the remote, or even a baby, under ideal conditions, but who don't have the focus and talent to use their skill 'in the real world'.

• I concur with this and i raise it, i think the force-sensitiveness is not genetic AT ALL. Skywalker's family was strong in it not because of genes but because of their presence in the axis of galactic events. – ThreeLifes Mar 29 '17 at 11:43

Not sure how broadly you need to limit the population, but if it's planet-local, you can induce conditions so that they're just not around. Most of them are usually off on missions saving the galaxy, negotiating truces, etc. Just like Star Wars Jedi Knights.

Or have sensitivity be determined not by one trait, but by a combination of rare traits. Like black hair and blue eyes.

• Hi, welcome to worldbuilding. It sounds like you've got an idea for an answer but it needs a little more fleshing out to fully address this question. – Lio Elbammalf Mar 20 '17 at 14:40

Go the Warhammer 40K route, scour the lands for "Psykers", humans with psionic potential and indoctrinate them via rigorous examinations to test their power and abilities, those who pass the stringent trials without death are indoctrinated some more before being put into a task force to find more psykers, while failures are placed on floating despot "black ships" to channel their energy to keep the god-emperor alive.

of course this all centers around indoctrination.

Easy. Cultivate a jedi religious or quasi-religious monastic order that separates the force sensitives from the rest of society and emphasizes the virtues of emotional moderation and asceticism. Your jedi order members will be trained to a high degree of capability and also be discouraged from 'disruptive' emotional distractions like marriages and girlfriends. If you make it an order that is not tied to a particular nation, but a world-wide system that emphasizes being apolitical and subordination to secular governments, it should be able to spread. Contributing a son or daughter to the order conveys an impressive amount of prestige, of course.

If sensitivity is a single recessive gene, then you have to have it from both parents for it to show. If having a single gene is somewhat selected against, then the occurrences in the general population is low.

So this becomes a gene like Tay Sachs disease or Huntington's chorea.

This however would make all the offspring of a sensitive be sensitive. Blue eyed parents have blue eyed kids. Brown eyed parents can carry the blue eyed gene masked, or be dual brown eyed.

(Eye colour is a bit more complex. There are ways that blue eyed parents can have brown eyed kids, but it is rare.)

Suppose that having a doubled sensitive gene makes you sterile. So there will be NO offspring from a sensitive?

Ok. Let's make it more complicated. Dominance of insensitive is not complete. Children who are genetically Is (Insensitive from one parent, sensitive from another) are trainable, can handle small tasks but are not Jedi material. If not trained, they have oddities -- lucky at dice. Unusually good marksmen, but not really remarkable.

Let's make it a bit more complex. Being sensitive to the force is polygenetic. Suppose that it is 4 genes, all recessive, If you have none of the genes you have the sensitivity of a rock. Any one of the genes gives you some slight sensitivity, any 2 gives you four as much, and 3, nine times as much, and all 4 16 times as much.

If each of these has an occurrence in the general population of 1 in 100, then you have 1% of the population has a trace, 1 in 10,000 has more than trace, 1 in a million has 3 genes, and is of Radagast the Brown capability (borrowing a metaphor) and all 4 genes is 1 in a hundred million that allows you to use LS monogrammed handkerchiefs. That is still 10 per billion, or aobut 70 on planet earth. Adjust the occurrence of the genes to suit.

This sort of thing allows you to create "Witches of Karres" universes where a people has self selected for these genes.

If you want to mix it up more, you can have each gene give specific traits/perceptions. (E.g. s1 gives perception of what isn't here. s2 gives you some perception of what isn't yet. s1 and s2 reenforce giving you greater distance/time sensitivity. s3 is the ability to fine tune and descriminate. s4 gives you the feel of the galactic overmind, or gives you the ability to cloak your own footprint on the force. Whatever.

Add more genes but make some less probable. Make some lethal when combined.

E.g. s5 reenforce with s6 makes you incredibly empathic, but so much so that if someone is killed near you you may die from the empathic shock.

Training affects all aspects.

I think that there is a mistake in thinking that there are genetic or biological factors at all in force sensitiveness.
First of all, the force is in all things, even Han Solo has shown remarkable speed and accuracy when shooting from the hip. Huts and Nomoidians are believe to be naturaly resistant to mental tricks, but this could be a product of their culture, which makes them wary of "things that look too god to be true" or "conveniently simple". SO it would be possible for any individual to achieve a level of understanding and limited use of the force simply by training. Skywalker's family is riddled with internal emotional conflict and external galaxy-shaping conflict. That could be very well why they are strong in the force and not their genes. I personally think that the force would regulate itself how many individuals achieve this kind of higher understanding of the force and when a sufficiently number is achieved there simply won't appear any more, no matter the trainings or breeding programmes.