This is inspired by GRRM's A Song of Ice and Fire, where for millennia House Targaryen wed brother to sister at all possible opportunities, and Aunt to nephew, Uncle to niece, and cousin to cousin where that was not possible. As a result, the family had a propensity for madness, and often times children born of such unions would be stillborn, or be born horribly deformed. By the end of their reign, 5 out of 8 children born to them were stillborn.

They only out-bred a few times, and notably before the Mad King triggered the collapse of their dynasty, three generations of complete out-breeding with people totally unrelated happened. This was extremely rare. Should I expect this, or is there a way to stop the genetic disorders associated with this strong inbreeding?

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    $\begingroup$ There's no way of stopping the problems with inbreeding unless your breeding pairs are genetically identical. Or you employ concubines and tight lips. $\endgroup$
    – user10945
    Sep 22, 2016 at 14:12
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    $\begingroup$ The word is "outbred", not "outbread". I'm not sure what "outbread" would even mean. Maybe something like Challah or Naan to someone who's only ever eaten Wonder bread? $\endgroup$ Sep 22, 2016 at 19:59
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    $\begingroup$ Don't the effects negate themselves? A succession of idiots taking the throne eventually ends the dynasty, leaving it open to folks who don't marry their cousins. $\endgroup$
    – EvilSnack
    Sep 24, 2016 at 23:13
  • $\begingroup$ Depends on how long is a "long" time, because dynasties do not last forever... $\endgroup$
    – AlexP
    Feb 20, 2017 at 17:15

9 Answers 9


The main problem with inbreeding is the genetic "pureness" you achieve. To cut it simple, let's assume genetics was working on mendel level (Wikipedia Link).

Each trait is inherited via two genes. Each gene can have one of two states: recessive and dominant. and father and mother each both pass on one gene to their children. So if we assume (another HRR martin reference incoming, obvious spoiler alert):

Hair color is being inherited as a single trait. you could have black Hair (B), or blonde hair (b). Black is dominant, blonde is recessive. So there are several possible gene-combinations:

BB (purebred black) Bb (mixed breed, but still black hair, because dominant beats recessive) bB (see above) bb (blonde).

So if we know that a father is BB, all his children will have black hair.

Now, i need to state something that i can't directly prove, but my memory telly me it is true: A lot of traits are composed in a way, that the "healthy" state is dominant, while the unhealthy state is recessive.

The problem with inbreeding is, that a lot of genetical defects, that wouldn't show up when mating with "purebred healthy"(HH) partners, will start to show up more often when "mixed breed healthy" (Hh) partners have children. It's gonna be especially bad when purebred unhealthy partners start having children. As i said, the purebred unhealthy traits are gonna be rare - most of them would normally marry a health partner, giving their children 50-100% chance to be healthy.

But when inbreeding, you selet from genetically similar partners - the chance of them being purebred unhealthy or at least mixed healthy is high - and so is the chance that your children will be unhealthy.

interesting sidefact: after a long period of strict inbreeding, the genetic variation will become less and less, leading to "typial" behaviours, looks and traits of an inbreeding population.

And since a LOT of things are usually determined by genetics, so it is generally not advisable to inbreed anything. Also, you cannot protect against the effects. you can just, from time to time, try to breed healthy individuals into your population to enrich the genetic pool.


There are 3 main issues with inbreeding...

  1. Recessive genes get reinforced.
  2. First generation have a reduced fertility.
  3. Immune systems are weaker generally due to genetic similarity, meaning that if 1 person lack an immunity most others will too.

So lets talk about these 3 things...

2 is not a problem, because 2 actually is a screening mechanism that prevents completely broke dna to breed.

3 just means that the probability of getting sick from one disease vs another is higher than someone in the general populace's. That is to say that if someone has a 1/100 chance to catch something in general populace, someone from the inbred line might have a 1/90 chance to catch something.

1 is the misunderstood one... In the most basic of terms you have dominant(D) alleles and recessive(d) alleles. There can be multiple alleles to a gene and each have different positions with regard each other.

You can have 1 of the following combinations...

  • DD
  • Dd (and the mirror which is written the same way)
  • dd

Each of these are made of 1 allele from a mother, and 1 from the father (obviously), each of them having 1 of the above sets...

So lets just go through a few generations assuming all possible combinations occur in their children...

G1a(DD) and G1b(dd) will have the following children:

  • G2a(Dd)

Yup that's it, but we haven't started the inbreeding yet, so let's continue...

G1a(DD) - G2a(Dd) breed and can produce the following

  • G3a(DD)
  • G3b(Dd)

G1b(dd) - G2a(Dd) can produce :

  • G3c(dd)
  • G3d(Dd)

So what we see here is that a mating of G1a and G2a is perfectly fine, but assuming the recessive trait is bad, G1b and G2a has a 75% of a having a child with the recessive that is a problem, so let's go down that path... where we see the problem emerge...

G2a(Dd) - G3c(dd) will get you :

  • G4a(Dd)
  • G4b(dd)

G2a(Dd) - G3c(Dd) will get you :

  • G4c(Dd)
  • G5d(DD)
  • G6e(dd)

In other words, this set up just give you an infinite loop, which sucks, but this is really rather normal so there is no real issue here. The issue comes when...

G3c(dd) - G4b(dd) mate and produce the following off spring :


Notice how there is 100% chance of this occuring? The recessive becomes 100% likely, but so long as you don't get 2 parents with both alleles recesive then you won't have this problem.

This being the case solution is simple, just make sure noone with 2 recessive mate with another one... or do the reverse and make sure they do, if the trait is positive. This is how all our dog breeds came into being so you might not want to...

  • $\begingroup$ Of note, you can dramatically cut down on (1) if you can test for the recessive allele (or at least expression of the disease) and STOP that person at least from mating with another carrier. The Ashkenazi jews do this with Tay-Sachs. $\endgroup$
    – Jason K
    Sep 22, 2016 at 19:42

Everyone has problematic and even lethal mutations in their genome, but they don’t affect us because they are compensated for. Humans have two copies of their genome and thus two copies of each of their genes. Random mutations frequently break or knock-out genes that we couldn’t live without, but because we still have one working copy we don’t even notice. When two unrelated people produce offspring they have a 50/50 chance of passing on their broken copy of a gene, but because it is extremely unlikely that their partner has a broken copy of the same gene their child will likely be just fine.

Inbreeding is a problem because when you produce offspring with someone related to you, the chance that they have a broken copy of the same gene that you do becomes quite high. For a brother and a sister who have 50% of their DNA in common that chance becomes 50%. If the brother and sister both have a broken copy of a gene then there is a 25% chance that a child of theirs will inherit both broken copies. This means if you mate with your sibling your child has a 12.5% of having a serious problem for each of your broken genes. The average person has on average 1-2 lethal mutations and likely many more mutations that would cause serious problems.

Now that we understand why inbreeding causes problems let’s look at how we can deal with it. The first thing to know is that inbreeding isn’t always harmful. If a lineage has no negative mutations or broken genes then inbreeding actually won’t cause any significant problems. We can see this principle at work in lab mice. These mice have been inbred so long that all of the negative, lethal mutations have been weeded out. This is because when two unrelated individuals mate all of their negative alleles are passed on normally because they don’t cause any harm. However, when two related individuals who are both carriers for a lethal disease mate then 1 out of 4 of their offspring will die before producing offspring of their own. This means that while both of the parents are carriers of the lethal disease, of their viable offspring only 2 out of 3 will be carriers. Over many generations this will gradually lead to the eradication of the negative trait.

So the first solution to our dynasty’s inbreeding woes it to just keep at it! If you successfully limit the influx of new blood into your family then after a few generations you will have eradicated the most harmful alleles. We can use a convenient tool to model this for the family: http://www.radford.edu/~rsheehy/Gen_flash/popgen/. Set the population size to that of a small family and change the fitness of the A2A2 genotype to 0. This represents A2 as a broken gene or recessive lethal allele. The result will look something like this: recessive lethalWhat we can see is that in only a few generations the A2 allele is completed removed from the gene pool.

If an allele is recessively lethal than as long as the family size is kept small and there is no breeding with anyone outside the starting population then the negative allele will effectively disappear in roughly 5-10 generations depending on chance and other variables. This means that if your dynasty can get past the first few generations most of the seriously negative traits will actually be eliminated from the bloodline.

But what about negative traits that aren’t lethal but are just bad? We can model this by changing the fitness of the A2A2 genotype to 0.9. This means the A2A2 genotype makes individuals about 90% as fit as individuals with an A1 allele.slightly negative recessive We see that when the selective pressure isn’t as strong random chance takes over and in some of the populations the bad A2 allele actually becomes fixed, meaning every individual in the family will now always have this slightly negative trait! What I didn’t tell you about lab mice, and this applies to other purebred animals, is that in the inbreeding process inevitably some bad traits become fixed and will decrease the overall fitness of the line. This means that while our dynasty is ridding itself of its serious, lethal alleles it will also be permanently gaining some less negative traits like hemophilia or madness!

So how can we stop these negative traits from becoming fixed in our dynasty? Well, one option is making these slight negative traits have a greater decrease in fitness than they would naturally. What I mean by this is if children who are born with hemophilia or other negative traits are prevented from reproducing, either through death, sterilization, or locking them away in a tall tower, then the fitness cost of that minor trait will be the same as the lethal traits we successfully got rid of. Essentially, by treating every negative trait as lethal we can get rid of them all in theory. In practice it’s unlikely that your dynasty will be able to produce children that are free of any and all of these negative traits, so you’ll have to make compromises just to have enough individuals to carry on the dynasty. Hypothetically though after only ~10 generations your dynasty should be stable and as long as you don’t outbreed with the impure rabble continued inbreeding won’t be a problem.

Another more creative solution to dealing with these slight negative traits might also provide a very interesting dynamic system. Imagine you have two ruling dynasties who only breed among themselves. Each of them has negative alleles that have become fixed making them relatively unhealthy. But if two individuals from the two dynasties have a child together then that child will likely be 100% healthy. This is called heterosis or hybrid vigor. It works because all of the negative traits of one family are going to be complemented by the positive allele from the other family. Thus, the heterozygous child will have one working version of all of its parent’s negative alleles. This leads to a very interesting dynamic where the two breeding populations are relatively unhealthy but when they crossbreed they can produce great leaders without health problems. The catch is those crossbred individuals can’t continue to inbreed or they will contaminate both families with each other’s negative traits and remove the benefit of the crossbreeding. So perhaps the most successful arrangement is the maintenance of two separate noble families who only crossbreed to produce rulers who will be forbidden from bearing their own offspring.

  • $\begingroup$ The biggest problem with breeding out traits is not that we can't do it, but no human culture is stable enough to maintain such breeding at least not in history. Maybe pre-history it was possible...if not probable. $\endgroup$
    – Durakken
    Sep 23, 2016 at 0:33

For some real world human genetics this paper analyses the pattern of lethal recessive genes in the Hutterites (who only intermarry within their own communities) and runs simulations to find out how such genes are eliminated or spread through their population.

Skip to the Discussion section at the end if you're not interested in the technical stuff. They have figures for the increased risk of having children who die from these lethal genes, but also point out that inbreeding can lead to the elimination of lethal recessive genes from a population. This is due to genetic drift - genes (both good and bad) get lost by chance if not many people in the founder population had them and/or the people who had them didn't pass them on to kids or grandkids.

So imagine the people of Westeros as a whole have these lethal recessive genes: eyebrow disease, earlobe disease and toenail disease. The first Targaryens to come up with the brother-sister marriage happen, by chance, not to carry the eyebrow disease genes. Therefore their descendants never have eyebrow disease. Similarly, they do carry the earlobe disease genes, but a few generations down the line there are a couple of princes - Prince A who inherits earlobe disease gene and Prince B who doesn't carry earlobe disease. If Prince A dies before having kids, then earlobe disease is also vanished from the royal line.

On the other hand, toenail disease genes are handed down every generation, and become more common than they are in the general Westeros population. Perhaps 1 person in 1000 has toenail disease in the general public, but 1 in 250 of the Targaryens has it.


Maybe, if you're willing to have a strong eugenic culture. And a strong stomach. a lot of forward planning, stability, and ideas that will let them work with genetics (doesn't have to be right ideas, mind, just close enough to let them function).

So, what your dynasty needs, is to generally practice having as many kids as possible. All the kids, really a dozen per individual or more is ideal - include any born out of wedlock or wrong side of the sheets, it will only help. Then, kill any kid that shows a negative genetic trait (madness, physical deformity, hemophilia, whatever) - and possibly even their kids, if it wasn't caught before they grew up and had kids of their own. That's why you need so many kids to start with, so that you can get rid of any who look like they've got unhealthy genes.

So, breeding too closely is a problem primarily because it increases the chance poor recessives come to the surface. Killing off anyone who shows these recessive traits will, over time, weed them out of the bloodline. Especially if anyone suspected of being a carrier is also discouraged from breeding. A lot of people would be killed for non-heritable problems, as well, since there would hard to tell if a problem that develops is actually environmental or heritable unless you've got a good genetic testing setup, or several generations to track and correlate. You will need a strongly planned family - every now and then the family can pick a negative trait and spend several generations trying to eliminate it (the madness, or weak eyes, or something) - since trying to fix them all at once might depopulate the family too much, and leave no one to breed it back up.

Eventually, your family line will hit a point where all the recessives are clean (because any who weren't got killed or banned from reproduction for so long). If this happens, everyone in the family will have virtually identical genetics, family characteristics will be very strong, variation will be very shallow. If something happens that the genetics don't have an answer for, like a new disease, they all die - but they will be very strong within those traits they do have, specialized. It's actually something like an artificially created genetic bottleneck, with the occasional infusions fresh genes from out-of-family marriages and bastard children possibly helping to keep the family line from self-destructing before then (and better yet if some of those fresh genes were chosen for traits they desired to breed into the line).

If it goes far enough, it will result in a breed apart - and I mean like a dog breed, with characteristic physical features (and problems), and their attendant tradeoffs. The occasional infusion of fresh genes should keep them from drifting into a new species - but it's on the horizon once they reach this point, and depending on the genetic drift of their surrounding population.


Today we can observer a 'genetic issue' with one of Indian's caste.

Because they normally only marry with members of same cast there a genetic mutation that's affect anestesia: "The frequency of genetic mutation increases when people marry within the community. This leads to genetic disorders. Vysyas of Andhra Pradesh who have been marrying within the group for several hundred generations suffer from a typical problem. When anesthesia is administered to any member of the community for surgery, they take much longer than others to come out of it. Some of them could suffer paralysis too." http://www.dnaindia.com/analysis/column-but-not-caste-in-stone-1882288

Another source: http://timesofindia.indiatimes.com/home/sunday-times/A-Chettiyar-problem/articleshow/1823598.cms

The problem will be worse in your case.


Perhaps you could limit the negative impact of incest by mixing new blood every other generation. Assume that the marriage of a dragon rider with a non dragon rider half their kids can ride dragons.

Assume that the marriage of two dragon riders result in all the children been dragon riders.

Assume that only the royal family is the only people with dragon riding blood.

Have two siblings with the same parents who are both dragon riders.
There kids are both dragon riders as well.

So the siblings mary outside of the family and produce a next generation half are dragon riders and the other half not.

For this new generation the royal family marriages the dragon riders children of one sibling would be paired in marriage with a dragon rider of the opposite sex produced by the other sibling [(aka cousin marriage instead of sibling marriage).

Cousin marriage has the same disadvantages as siblings marriage, but to much lesser extent. Madness for example would be less frequently with the Targaryen if they married Cousins instead of sibling.

Also because they marry outside the family every other generation they receive new genetic material this prevents genetics stagnation.

On a side note it also would encourage the royal family to have several bastard every other generation so that they will have as as many dragon riding half blood pairs to produce the Next Generation of full-blood Dragon Riders.


The lo-tech technique (As apparently used in Egypt) is for your queens to have illicit affairs with the higher ranking palace guards; the resultant children being genetically healthier due to outbreeding.

Due to the requirements of heirs being produced in marriages, it doesn't work with kings going off with concubines.

So to negate the effects.. just make sure that your queens have plenty of private time and your palace guard are chosen for their health and physique. Your dynasty can go on forever..


Short, but probably unpopular, answer:

By having lots of women.

Start by selecting the males aggressively. Only the ones considered flawless get to breed and can enter the line of succession. The others will make a sacrifice of blood royal for Great God Cthulhu. Or Bhaal or whatever. The rituals should be highly theatrical and public. Providing entertainment for the mob is the primary function of royalty, anyway.

The heir is elected by all "flawless" males of the blood royal from among themselves. You could even have something like the princes electing the king for a fixed term. As you are talking about a very exclusive group of closely related people you could probably get away with short terms without undue distraction. I think a "king for a year" would be practical.

The point here is too keep the available, already limited, gene pool open and combined. You can't really afford to throw away people of blood royal just because their grandfather was the second and not the the first son. The strict term limit also should reduce issues with insanity and other mental shortcomings.

The second part is to have lots of children. And since birth rates are capped on women that means polygamy. Probably concubinage as well. Sons of wives who are considered flawed or of concubines would feed great Bhaal. Daughters would be eligible to be wives. You can't afford to lose diversity and fertility by culling females.

Concubinage would be used to introduce a safety mechanism in case of genetic diversity becoming too low. It would also be used as a reward to nobility and to bind them to the royal house by blood. This way none of the nobility could claim a drop of royal blood, but could be proud of there being some of their blood on the throne. Number and existence of concubines would depend on the number of wives producing viable offspring. There might be none or they might outnumber the actual wives.

The weak part of this solution is the selection process. Left to their own devices humans will select for or against traits they really should not. In war like cultures, men might be selected for aggression and within few generations the entire family would be homicidal psychopaths. Our own political systems elect leaders based on their ability to manipulate groups of people to trust them with no consideration given for competence to do the actual work. (<- Not a Trump reference. While you can argue he took advantage of this, this is in no way his fault. It is how the system works for ALL politicians.)

So you'd need to either keep the selection criteria off the camera or give it lots of careful thought. I strongly recommend the first. As I said, humans have a tendency to get this wrong, and I assume most readers of this post belong to that group. For that matter, without genetic engineering or magic, human ability to do selective breeding on humans is limited due to traits interacting with each other and the environment. So there will be unintended consequences and diminishing gains as number of traits increase does apply.


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