Why would institutionalized breeding lead to a lack of genetic diversity?

[Sharad9]

This world is very different from ours in that it historically revolves around matriarchial civilizations. Families are based around a clan-like system, in which people remain into the clan they are born into. One world religion has formed which has historically held women to be the dominant sex, as they are the bearers of life responsible for creating the next generation, and due to their abilit to perform magic. Men are meant to be helpers to females and defenders of society, culturally taking on defense, security, and labor roles.

Creating new life is seen as a religious duty and undertaking. Therefore, it generally is controlled and regulated through a system of institutionalized breeding between clans, in which males are chosen to mate with females. Alpha males who are successful in society through war, skill in a certain trade, etc. Are chosen to represent their clans in this manner. These are usually arranged by councils which are led by a clan matriarch, and are the basis for alliances or trade deals, similiar to how royalty used marriage in our world. All children produced by this union belong to the women's clan, and they are raised communally. Father figures would normally be relatives from her close family, with the community being an extension of that. Females are also their own form of birth control, and have the biological ability to choose when to get pregnant.

Would this controlled form of human reproduction lead to a lack of genetic diversity among the population?

[lunaticfringe]

It depends on what traits the Society viewed as valuable. They may accidentally breed out a trait that may be useful in the future or isn't considered desirable at the moment.

Mild or institutional incest might occur. Royal or lines descended from the gods might be desirable culturally. Thus leading to the idea that those bloodlines be kept 'pure'.

People are ****ing weird. Cultural Memes aren't really based on consistent logic.

[Nightcanon]

It depends to what extent you mean breeding is generally inter-clan rather than intra-clan (are literally all matings with males from outside the clan, or just the politically important ones? Do some women still have children with the girl next door?) How big are the clans, how many and how widely do they travel? Have there been mass migrations in the past?
At one end of the scale, if clans are little more than an extended family and clans A, B and C only ever have contact with each other that would be quite limiting (it is possible to deduce founder mutations for autosomal recessive disease in British Asian and Irish Traveller populations, which in the past have effectively been small family-based clans that interbred with a limited number of other clans; European royal families are another example of this).
On the other hand, if there are essentially large numbers of males from each clan fathering offspring in several clans, that's potentially more diversity than occurs on average in current Earth populations (where even some people mate with people from halfway round the world, some people do still marry the person they met at primary school). This assumes that genetics works as it does in real life, of course.
Another possible thing to factor in, depending on how 'Game of Thrones' you want to get, is the effect of non-consensual intercourse, and whether it has the same effects in a universe where females can choose whether or not they get pregnant. Then again, if wandering bands of males are being invited to share their genes with local girls that might have a similar effect.
How much do people understand of genetics and selective breeding?(there is evidence that horse breeders in particular, but also dog breeders, had a pretty good understanding of which features 'bred true', i.e. were dominant, and which were recessive, going back way beyond Mendel in the mid 19c). Again, if breeding deliberately for genetic diversity, genetic diversity would be increased; conversely, breeding for desired traits in a very controlled way could mean that diversity is reduced (90% of the children in this generation of clan A were sired by Bob the Strong, with the remainder mainly being children of Clive the wise from clan C; Bob's father was Andy the Strong from clan A meaning many of these could be first-cousin consanginous matings if clan A is small).

[Solaris]

Yes, it would lead to a lack of genetic diversity as desirable traits are reserved and proliferated, while undesirable traits are stamped out. Just look at literally any product of selective breeding as compared to the wild stock.

[Sharad9]

Yes, it would lead to a lack of genetic diversity as desirable traits are reserved and proliferated, while undesirable traits are stamped out. Just look at literally any product of selective breeding as compared to the wild stock.

Is it guaranteed that those desirable traits eventually become undesirable at some point?

[Solaris]

Is it guaranteed that those desirable traits eventually become undesirable at some point?

I don't see why it would be a necessity, especially given the cultural stasis you find in a lot of settings, but as lunaticfringe said... sometimes there are unintended consequences. For example, breeding dogs to be larger has led to health issues like hip dysplasia, and Honeycrisp apple trees are some of the finickiest, whiniest little pansies to embarrass the rose family since actual pansies. Unless you have a society with remarkable understanding of genetics and inheritance, you're either going to run into some unforeseen problems or the selective breeding isn't.

[Mutazoia]

I don't see why it would be a necessity, especially given the cultural stasis you find in a lot of settings, but as lunaticfringe said... sometimes there are unintended consequences. For example, breeding dogs to be larger has led to health issues like hip dysplasia, and Honeycrisp apple trees are some of the finickiest, whiniest little pansies to embarrass the rose family since actual pansies. Unless you have a society with remarkable understanding of genetics and inheritance, you're either going to run into some unforeseen problems or the selective breeding isn't.

It can get much, much worse.

Here in the IRL 21st century, most people have at least a passing knowledge of dominant and recessive genes. In a fantasy/medieval society, not so much. So while they are breeding for a certain trait, they are also breeding in and re-enforcing the unknown recessives as well. If you are lucky, you only breed in the trait for sterility and your society either brings in fresh genetic stock or dies out. If your unlucky, you get a race of mentally stunted elephant people, who also happen to have the one great trait you were trying to breed for, and breed like crazy (think of the movie "Idiocracy").

[Sharad9]

It can get much, much worse.

Here in the IRL 21st century, most people have at least a passing knowledge of dominant and recessive genes. In a fantasy/medieval society, not so much. So while they are breeding for a certain trait, they are also breeding in and re-enforcing the unknown recessives as well. If you are lucky, you only breed in the trait for sterility and your society either brings in fresh genetic stock or dies out. If your unlucky, you get a race of mentally stunted elephant people, who also happen to have the one great trait you were trying to breed for, and breed like crazy (think of the movie "Idiocracy").

But up to date genetic records are kept that track that kind of thing. Shouldnt that prevent inbreeding from happening, and stop any jeoffrey lannisters from being born?

[Mutazoia]

But up to date genetic records are kept that track that kind of thing. Shouldnt that prevent inbreeding from happening, and stop any jeoffrey lannisters from being born?

It depends on the tech level of said society, but eventually the answer is still "no". Up to date genetic records of the detail necessary would necessitate a tech level a century or two (at leas) ahead of anything we can do here and now. But even so, you are eventually get to a point where the only people in the society that you are not technically first cousins to, will be your immediate family. Larger communities will hit this limit later than smaller ones, but it's only a matter of time Think of the Asgardians from SG-1. They spent centuries cloning themselves to the point where it was impossible to introduce new genetic samples and the entire species was doomed to stagnation. And that was just with cloning. Now imagine centuries of inbreeding...

[martixy]

External breeding control would probably result in what dog breeding looks today.

[Anymage]

Genetic? People are raw soul-stuff that's housed in a body formed by the right balance of the elements. Owls and bears can be hybridized, and dragons can crossbreed with just about everything. That whole theory about life being composed of squiggly little machines has been soundly disproven.

You can probably do something to cover why brothers and sisters or other close relatives mating is not a good idea in the long run. Their energies being too similar when you need some conflict for a properly robust new spirit, or being too insular pissing off the magic gods, or whatever. But as soon as the words "magical pregnancy" left your mouth, you stopped needing to be bound to modern concepts of population genetics.

[Knaight]

Selective breeding dropping genetic diversity is basically inevitable, and in the described case sounds like it's accompanied by deliberate small scale bottlenecking which just makes that faster. There's also some inherent dangers to low genetic diversity even if you don't accidentally exacerbate unknown deleterious traits, with disease being particularly major. Well adapted diseases for any member of the species are well adapted for every member of the species; we've seen this before with crop blights and currently largely hold that at bay with pesticides.

Genetic? People are raw soul-stuff that's housed in a body formed by the right balance of the elements. Owls and bears can be hybridized, and dragons can crossbreed with just about everything. That whole theory about life being composed of squiggly little machines has been soundly disproven.

That this was a D&D setting was never indicated, and if details on genetics are being looked for it's probably not because this view has just never been considered - it's because it's been rejected.

[Sharad9]

Selective breeding dropping genetic diversity is basically inevitable, and in the described case sounds like it's accompanied by deliberate small scale bottlenecking which just makes that faster. There's also some inherent dangers to low genetic diversity even if you don't accidentally exacerbate unknown deleterious traits, with disease being particularly major. Well adapted diseases for any member of the species are well adapted for every member of the species; we've seen this before with crop blights and currently largely hold that at bay with pesticides.


That this was a D&D setting was never indicated, and if details on genetics are being looked for it's probably not because this view has just never been considered - it's because it's been rejected.

I never actually considered that idea. It sounds interesting and possibly feasible.

[Solaris]

Genetic? People are raw soul-stuff that's housed in a body formed by the right balance of the elements. Owls and bears can be hybridized, and dragons can crossbreed with just about everything. That whole theory about life being composed of squiggly little machines has been soundly disproven.

You can probably do something to cover why brothers and sisters or other close relatives mating is not a good idea in the long run. Their energies being too similar when you need some conflict for a properly robust new spirit, or being too insular pissing off the magic gods, or whatever. But as soon as the words "magical pregnancy" left your mouth, you stopped needing to be bound to modern concepts of population genetics.

So?
Mendel had no idea that genes even existed when he did the experiments that (among other things) explained selective breeding. It doesn't matter what we call them - either we have selective breeding as a thing and we have something that works like genes, or we have neither. Likewise, you can either have selective breeding and reducing gene pools, or we can have neither. If you posit an infinite number of combinations within a species's traits resulting from two of the species breeding together, then selectively breeding for a trait becomes impossible. Genetics have to be heritable for selective breeding to work. You have to reduce the gene pool for selective breeding to work.
That's not to say we're all going to result with inbred hillbillies, mind. It takes several generations for inbreeding depression to start showing, and countless thousands before they stop being able to reproduce with the general population. Outcrossing to introduce (or reintroduce) useful traits is something we were doing even before we knew what genes were.

If we do away with heritable genetics entirely and yet come up with the desired result, we are simply going with "A wizard did it!" levels of not bothering. If that's what Sharad9 wants to go with, fine, but so long as everyone involved understands that it won't be internally consistent or terribly logical.

EDIT: I'm not just pulling these things out my butt. I breed things for a hobby. I'm working on establishing a true-breeding tomato cultivar from a hybrid, and have several lines of guppies going. I've researched the subject a wee bit.

[Bohandas]

As stated it probably wouldn't be a problem and might actually increase local diversity by promoting gene exchange between groups.

More intense forms of control however would likely lead to both loss of diversity and also the kind of maladies associated with purebred dogs.

[brian 333]

Culture wide selective breeding, (A Brave New World is an example,) would isolate 'undesirable genes' and prohibit their being bred back into the line. In the short run this is desirable because it can help eliminate some genetic defects. Humans do this naturally anyway by females refusing to mate with deformed males. There are zero genetic deformities linked to the human Y chromosome. Males, on the other hand, are far less discriminating.

However, 'undesirable genes' have purposes, even if we don't always know them. For example, the sickle cell trait causes many problems, but there is evidence sickle cell developed as a response to malaria, and people with the trait are more resistant to the disease. Cull the population of the sickle cell mutation and an evolution of malaria into a super-bug could wipe out humanity.

If you look around our world you see periodic isolation of cultures which allow them to develop survival traits which differ from the survival traits found elsewhere. Then the isolated culture is exposed to other isolated cultures for varying degrees of crossbreeding. The children of such crossbreeding are sometimes, but not always, more attractive, healthier, and more vigorous than either parents' native stock.

Just crossbreeding won't do it. Randomly mixing genes across a whole species simply homogenizes what is there. There must also be periodic isolations which allow natural selection to isolate favorable traits which become established mutations in the breed. Without the physical isolation of populations, survival traits and counter-survival traits simply continue more or less in the same proportions for generation after generation, leading to genetic stagnation. (Also, everyone eventually would look the same.)

[raygun goth]

Australian Aboriginal groups have a fairly complex system for preventing inbreeding.

Another thing you might want to read is the stuff about William Muir's experiments with chicken eugenics and what Hell was unleashed when he tried.