Inbreeding

[eyesOpened]

I'm bringing a question which arose on a different (non-science) forum. The question arose like this (paraphrasing):

 

Inbreeding is unethical because of the high chances of birth defects. Birth defects are caused by similar genes. If you keep a gene that may cause a birth defect in one family, there are no other genes to dillute the birth defect gene.

What's to say that similar genes won't just as likely cause "birth enhancements", where "enhancement" means the opposite of "defect"?

Most of the odd things tied to recessive genes in humans are defects.

What basis is there for this assertion?

Science.

Has this alleged "science" ever been published, and if so, where specifically can it be read?

What do you all think?

[Phi for All]

I'm not sure about it being unethical. Is it unethical for a woman in her early 40s to have a child because of an increased possibility for Down syndrome?

 

Brother/sister mating is taking an awful chance of a child with a dangerous disorder. I would call father/daughter or mother/son matings unethical, but more for the abuse of authority than for the possibility of birth defects.

 

This all assumes it's not a multi-generational situation. You increase the possibilities of having a child with an autosomal recessive disorder with inbreeding, but they're not so easily activated within a single generation. And the closer the relation of the parents, the more likely their child is to pick up a pair of bad recessive alleles.

[eyesOpened]

I complicated my question unnecessarily by introducing the notion of "ethics" into the mix. My concern, for the sake of this thread, is with the assertion: "Most of the odd things tied to recessive genes in humans are defects." That seems to be a popular assumption, but I know of no science supporting it. I understand that inbreeding would increase the probability of certain "autosomal recessive" disorders; but might it not just as well increase the probability of certain "autosomal recessive" enhancements (e.g., an autosomal recessive immunity to some disease)? I don't see where recessive traits got a bad rap.

[dmaiski]

im not an ethical person (some people have called me extremely pragmatic)

so ill state the practical point of view

 

inbreeding increases the similarity between individuals in a localized population

should an event arise that threatens the populations survival (a disease is a great example)

a population with a high level of inbreeding will lack the variability throughout the population

and will have a very high chance of dying out

 

(this is the main argument against inbreeding (lowering the gene pool) and its an argument from the point of population genetics, not focused on individuals or specific traits)

 

the argument that inbreeding causes birth defects is as far (as i know) a lot of hot air

there is plenty of evidence against it(just look at plants(self fertilization), plenty of examples of inbreeding in lab mice, animal breeders)

 

yes there are genetic defects tied to receive genes, also there are defects tied to dominant genes, co dominant genes, various allele combinations, lethal gene combinations and anything else you can think of

in a random mating you are less likely to get a rare trait expressed then you are with siblings, but at the end of the day its all luck of the draw (and depending on your genetics you may be better off screwing your siblings)

 

all the negative effects of incest have seen in a quick search resulted psychobabel, or geneologys of long dead kings/queens(which in my opinion is, for the most part, worthless as evidence of anything)

 

 

[Derin]

The reason that defects are more often ties to recessives is simple: they're less likely to get weeded out.

 

The more dominant a gene is, the more it arises and the more it is "exposed" to evolutionary forces. So dominant genes tend to succeed or fail more rapidly. Recessive genes will "hide" in a population in heterozygous individuals. (This is of course a simplification, as many genes will have a small amount of influence in heterozygous bodies and a lot in homozygous bodies, and that influence won't necessarily have the same effect -- a common example being sickle cell anaemia in malaria-infected countries.)

 

It's not that we have a lot of deleterous recessives, it's that we have very few deleterous dominants. They can't "hide".

 

So far as inbreeding goes, the dangers are greatly exaggerated and the morality is inconsistent. (Why is it morally good to insist that cousins don't breed and morally bad to insist that cystic fibrosis carriers don't?)

[jp255]

There is a positive correlation between the vigor/health of most organisms and heterozygosity, the term to describe this is heterosis. It is most widely accepted in plants. The data supporting heterosis in humans is not so strong as it is limited to a a small number of traits, so at best it is suggestive evidence at the moment. That being said a number of papers have found significant differences between inbred and outbred individuals, an example of such a paper is this one by H. Campbell et al. (2006) http://hmg.oxfordjournals.org/content/16/2/233.long

 

The negatives of inbreeding are well known in a number of species too. So I definitely wouldn't support a consanguinous marriage or inbreeding in general, as there is evidence to suggest that it could lead to children which are unhealthier.

 

The whole ethical issue. I consider it unethical, but there are other issues which annoy me more. The issue that other diseases, such as Huntington's disease, are still prevalent today (at a higher frequency than I would like) and they are not considered unethical as far as I am aware. If they were considered unethical, and people that know they have it or if they don't but know there is a chance they could, then it would not be a prevalent as it is. The prevalence would purely be due to de novo mutations. I remember not so long ago there was a story in the news about people smoking around children (the children had breathing difficulty or something), the way it was presented suggested that it was not unethical.

 

There are many things which are unethical, but are clearly not considered to be unethical.

 

"Most of the odd things tied to recessive genes in humans are defects."

 

It is like Derin said. Dominant genetic diseases can be eliminated from populations much faster than recessive traits by natural selection. So this can explain a high number of recessive conditions being present in the population at any one time. Also it is a lot easier for recessive alleles to hitchike to high frequency, and they can provide heterozygous advantage and therefore be subject to balancing selection, Derin provided the malaria example.

 

It could also be that more genes are haplosufficient rather than haploinsufficient.

[Phi for All]

So far as inbreeding goes, the dangers are greatly exaggerated and the morality is inconsistent. (Why is it morally good to insist that cousins don't breed and morally bad to insist that cystic fibrosis carriers don't?)

Since the dangers of inbreeding increase if practiced through multiple generations though, the taboo probably is morally consistent given the propinquity of family units. Remove the taboo and you'd be much more likely to have close relatives breeding exclusively with each other over time.

[Derin]

Since the dangers of inbreeding increase if practiced through multiple generations though, the taboo probably is morally consistent given the propinquity of family units. Remove the taboo and you'd be much more likely to have close relatives breeding exclusively with each other over time.

 

I meant that it's not consistent with other mainstream opinions and practises of eugenics. A ban on inbreeding has enough support to be law and a ban on cystic fibrosis sufferers having children with each other does not, despite the chances of inheriting CF in such circumstances far outweighing the dangers of inbreeding (where the inbreeding subjects are not knowingly carrying a particularly bad genetic disorder). Our society is generally anti-legally enforced eugenics except for an inbreeding exception.

 

I don't think you would get high rates of inbreeding by abolishing such laws. There is the possibility of adopted individuals inbreeding, but by and large the Westermarck effect is pretty good. Inbreeding is usually related to marriages of social, diplomatic or economic advantage, which doesn't happen much with modern Western society, although I don't know enough about the rest of the world to have a stance on them. (Indeed, the taboo on cousin marriages is a result of encouraging royal families to interbreed with each other to strengthen ties, instead of within their own family to cement royal claims.) But that's getting off-topic.

[dmaiski]

what relay gets my interest in this case is "why do people hate incest so much"

its probably because i did not have any kind of indoctrination into human society (i completely ignored most people unless they were interesting)

but i don’t see what is morally wrong with it

 

its probably just me and a question for sociology, but can someone spell it out to me "why is it wrong" in simple referenced English language

 

 

[Phi for All]

As I said before, moral justifications would seem to be confined to extremely close familial relationships where there might be an abuse of authority component. Mother/son and father/daughter matings are highly suspect in this regard. Aunts and uncles mating with their respective nephews and nieces probably also fall into this category. This suspicion probably flows naturally, and perhaps undeservedly, into less close relationships between cousins.

 

Mating with a first cousin has its dangers, but I think the real reason it's considered "wrong" is because many such matings don't happen in isolation, and there is evidence to suspect such prolonged matings within a population do produce harmful genetic disorders. Iirc, the European royalty had at least 20 cases of hemophilia within three or four generations of cousin marriages from the Victorian era.

[MattyG]

I complicated my question unnecessarily by introducing the notion of "ethics" into the mix. My concern, for the sake of this thread, is with the assertion: "Most of the odd things tied to recessive genes in humans are defects." That seems to be a popular assumption, but I know of no science supporting it. I understand that inbreeding would increase the probability of certain "autosomal recessive" disorders; but might it not just as well increase the probability of certain "autosomal recessive" enhancements (e.g., an autosomal recessive immunity to some disease)? I don't see where recessive traits got a bad rap.

 

I would like to clarify eyesOpened's argument. I'm on the other forum to which he posted this question. He posted the question to The Cauldron: A Pagan Forum, asking us "So, what are the Pagan beliefs and practices with respect to incest?" If this post was not meant to deal with ethics, I can't imagine why he would be posting it to a pagan religious forum. The consensus of the forum was that we are opposed to incest as it frequently causes negative, recessive traits to become manifest. He argued against us (using Wikipedia as his only source), saying that there's no proof that recessive traits couldn't be positive. He continuously asked us to provide proof that there were no recessive genes that manifest positively with two copies, because he doesn't understand how burden of proof works, or how it's relevant to the conversation.

 

Additionally, when asked why he was asking us, a group of pagans, about this primarily scientific phenomenon, he said he wanted an opinion from people who "might be less terrorized and brainwashed by the Bible," as if Christianity is the only plausible reason why someone would be against incest. Additionally, he said that he was "intrigued by the idea of using incest as a means to creating an enhanced sub-species with reproductive advantages." So that's the context of this discussion.

[eyesOpened]

I would like to clarify eyesOpened's argument. I'm on the other forum to which he posted this question. He posted the question to The Cauldron: A Pagan Forum, asking us "So, what are the Pagan beliefs and practices with respect to incest?" If this post was not meant to deal with ethics, I can't imagine why he would be posting it to a pagan religious forum. The consensus of the forum was that we are opposed to incest as it frequently causes negative, recessive traits to become manifest. He argued against us (using Wikipedia as his only source), saying that there's no proof that recessive traits couldn't be positive. He continuously asked us to provide proof that there were no recessive genes that manifest positively with two copies, because he doesn't understand how burden of proof works, or how it's relevant to the conversation.

 

Additionally, when asked why he was asking us, a group of pagans, about this primarily scientific phenomenon, he said he wanted an opinion from people who "might be less terrorized and brainwashed by the Bible," as if Christianity is the only plausible reason why someone would be against incest. Additionally, he said that he was "intrigued by the idea of using incest as a means to creating an enhanced sub-species with reproductive advantages." So that's the context of this discussion.

That's about 50% accurate and 100% irrelevant.

[Derin]

I don't know what reproductive advantages means in this case, but we do use inbreeding to human advantage. Not just for show animal breeding (which is a brilliant example of the problems caused by extreme inbreeding), but to create genetically near-identical subjects for animal trials.

 

Phi, any mating between somebody and the person who raised them is morally questionable due to the element of power. I don't think their genetics are relevant.

 

Dmaiski, the human aversion to incest is probably based on a mixture of general disgust at the idea due to the Westermarck effect (look at the banning and/or penalties against homosexual unions in many countries based on personal disgust), and the fact that the ban is how the laws currently stand, so is considered default. (The laws themselves came in to encourage royalty to marry outside their own families and help strengthen ties with other countries.)

 

 

[MattyG]

I don't know what reproductive advantages means in this case, but we do use inbreeding to human advantage. Not just for show animal breeding (which is a brilliant example of the problems caused by extreme inbreeding), but to create genetically near-identical subjects for animal trials.

 

Phi, any mating between somebody and the person who raised them is morally questionable due to the element of power. I don't think their genetics are relevant.

 

Dmaiski, the human aversion to incest is probably based on a mixture of general disgust at the idea due to the Westermarck effect (look at the banning and/or penalties against homosexual unions in many countries based on personal disgust), and the fact that the ban is how the laws currently stand, so is considered default. (The laws themselves came in to encourage royalty to marry outside their own families and help strengthen ties with other countries.)

 

 

 

Yeah, no one on the Pagan forum is quite sure what he wants either, or why he's asking us non-scientists about it.

 

I do think it's a little unfair to say that the genetics are completely irrelevant. Humanity as a species thrives when we have a varied and diverse gene pool. That's most likely why we evolved things like the Westermark effect. And like you said, show animal breeding is a perfect example of why incest really isn't a good idea. Personally, I believe the ethical implications come from the fact that 1) You're exposing your child to the increased risk of negative, recessive traits, and 2) You're decreasing the diversity of the human genome. Just a personal belief though. Personally, I don't think I would legislate against two related adults choosing to be incestuous, but I certainly would place societal pressure on them to avoid that behavior. Especially if it was being done to create some kind of master-race. That always works out so well.

[Phi for All]

Phi, any mating between somebody and the person who raised them is morally questionable due to the element of power.

Now why does that sound so familiar?

 

I don't think their genetics are relevant.

dmaiski asked why incest was wrong, and you don't think genetics has any relevancy?

[eyesOpened]

The Pagans have a grotesque fetish with worshipping gods who are incestuous. The only cause unifying their perverted "religion" seems to be the promotion of parent/child power-abuse. Through a program aimed at manipulating the population's genetic composition -- i.e., "eugenics" -- they seek to create a "master-race" characterized by cystic-fibrosis, nearsightedness, extra-digits, fused-digits, missing-joints, limb-dwarfing, and clubbed-thumbs.

 

I'm trying to digest the information posted in this thread. I will need to research a little to understand all the language. If I understand correctly, inbreeding would slow or stop the proliferation of recessive defects. I'm trying to formulate mathematical models of the dynamics in issue here, but I have nothing worth posting yet.

Edited September 11, 2012 by eyesOpened

[MattyG]

The Pagans have a grotesque fetish with worshipping gods who are incestuous. The only cause unifying their perverted "religion" seems to be the promotion of parent/child power-abuse. Through a program aimed at manipulating the population's genetic composition -- i.e., "eugenics" -- they seek to create a "master-race" characterized by cystic-fibrosis, nearsightedness, extra-digits, fused-digits, missing-joints, limb-dwarfing, and clubbed-thumbs.

 

I'm trying to digest the information posted in this thread. I will need to research a little to understand all the language. If I understand correctly, inbreeding would slow or stop the proliferation of recessive defects. I'm trying to formulate mathematical models of the dynamics in issue here, but I have nothing worth posting yet.

 

So yeah, this guy decided to argue with the moderators when they called him out for breaking several of the forum's rules, so they banned him. Now he's just whining to whoever will listen I guess.

 

As a member of the pagan community, I hope no one is taking him seriously.

 

To anyone interested, here's the original thread he posted to. http://www.ecauldron.com/forum/showthread.php?4567-Incest-Question

Edited September 11, 2012 by MattyG

[eyesOpened]

The only people who care about pagans are pagans. This forum is about genetics.

 

 

[MattyG]

The only people who care about pagans are pagans. This forum is about genetics.

 

 

 

If that's so, why were you on our forum?

 

Also: "If I understand correctly, inbreeding would slow or stop the proliferation of recessive defects."

Did you actually read the comments on this forum? Because no one here's said anything like that. At all. They've said the opposite.

[Ringer]

The Pagans have a grotesque fetish with worshipping gods who are incestuous. The only cause unifying their perverted "religion" seems to be the promotion of parent/child power-abuse. Through a program aimed at manipulating the population's genetic composition -- i.e., "eugenics" -- they seek to create a "master-race" characterized by cystic-fibrosis, nearsightedness, extra-digits, fused-digits, missing-joints, limb-dwarfing, and clubbed-thumbs.

 

I'm trying to digest the information posted in this thread. I will need to research a little to understand all the language. If I understand correctly, inbreeding would slow or stop the proliferation of recessive defects. I'm trying to formulate mathematical models of the dynamics in issue here, but I have nothing worth posting yet.

 

The majority of the religions I know of have no qualms with inbreeding being a major part of them.

[MattyG]

The majority of the religions I know of have no qualms with inbreeding being a major part of them.

 

Very true. On our forum we gave the explanation that most of us see myth as being symbolic, rather than literal and, therefore, depictions of incest are meant to be poetic rather than pro-incest. Additionally, we acknowledge that whatever the gods are, they are not biological organisms, and not susceptible to negative recessive traits.

[eyesOpened]

Very true. On our forum we gave the explanation that most of us see myth as being symbolic, rather than literal and, therefore, depictions of incest are meant to be poetic rather than pro-incest. Additionally, we acknowledge that whatever the gods are, they are not biological organisms, and not susceptible to negative recessive traits.

symbolic, non-literal, poetic promotion of parent/child power-abuse.

[MattyG]

symbolic, non-literal, poetic promotion of parent/child power-abuse.

 

Yeah, still not sure where he got that from, seeing how we've all been very anti parent-child incest, but I suppose you can't argue with crazy.

[eyesOpened]

The reason that defects are more often ties to recessives is simple: they're less likely to get weeded out.

 

The more dominant a gene is, the more it arises and the more it is "exposed" to evolutionary forces. So dominant genes tend to succeed or fail more rapidly. Recessive genes will "hide" in a population in heterozygous individuals.)

 

It's not that we have a lot of deleterous recessives, it's that we have very few deleterous dominants. They can't "hide".

The terminology in jp255's post in particular, and in the article he cites, is is new to me, so my understanding will be delayed until I research.

 

Suppose that we start with a gene pool where half the recessive genes carry defects, and the other half carry enhancements. Suppose also that there are no mutations. The evolution of that system would lead to a state where recessive enhancements would outnumber the recessive defects.

 

Now if we consider a system that's similar but also has mutations, it matters whether mutations tend to create enhancements or whether they tend to create defects. Do real-world mutations have either tendency?

[MattyG]

Suppose that we start with a gene pool where half the recessive genes carry defects, and the other half carry enhancements. Suppose also that there are no mutations. The evolution of that system would lead to a state where recessive enhancements would outnumber the recessive defects.

 

The system you're describing is woefully vague. What are the dominant genes that respond to the recessive? Are you describing only one particular gene, or just the total gene pool? Are we to understand that these are negative effects that significantly affect the ability to survive and breed? Do the positive genes significantly increase the ability to survive and breed?

 

A single trait does not have two different recessive genes that code for something. One possible gene will be dominant and one will be recessive (clearly I'm simplifying this to a simple two-gene trait for the purpose of the argument).

 

Let's try a thought experiment in a standard society where excessive inbreeding does not occur. We will look at a negative gene that causes infant mortality, and a positive gene that prevents infant mortality. These are the possibilities.

 

Dom= good, Rec=bad

People will survive if they have even one Dom gene, but die if they have two Rec genes. Since anyone with one Dom and one Rec will survive and reproduce without knowing they have the Rec gene, the Rec gene will survive in the population. Inbreeding, working how it works, will cause instances of the Rec gene to increase, causing more children who will die from the defect.

 

Dom=bad, Rec=good

People will survive if they have two Rec genes, but will die if they have even one Dom. Anyone with the Dom gene will die, preventing them from surviving and breeding. Therefore, the population will quickly have only the Rec gene. Incest is unnecessary to increase instances of the Rec gene since natural selection has already selected against the negative Dom gene.

 

As demonstrated through the thought experiment, inbreeding is unnecessary to promote the prevalence of positive recessive genes. Natural selection already does that. Additionally, incest can only serve to increase negative or inconsequential recessive genes. That's as simple an explanation of human genetics as I can give.

 

Addition: Just realized I could add an example like Sickle Cell Anemia where a DomRec will prevent future disease

 

So now, Dom=good, Rec=bad, DomRec=best

People will survive if they have even one Dom gene, but they die if they have two Rec genes. However, people with both a Dom gene and a Rec gene will live and breed longer than someone with two Doms, because they have an added immunity to some disease (we'll just say influenza). You have a similar situation as "Dom=bad, Rec=good," except the Rec gene will be more pervasive in society since it does, occasionally, provide a benefit. In this case, inbreeding will lead to more people with two Dom genes, or two Rec genes. This is bad for society since it minimizes the maximum number of healthy people. Ideally, if you are DomRec, you want to breed with a DomDom, because, statistically, 0% of your children will suffer infant mortality, and 50% will be resistant to influenza.

Now I know what you're thinking. "Now they have 50% of their children DomDom, and 50% DomRec. Clearly those children should reproduce in order to maximize the next generation's gene-pool. However, in this scenario we're assuming that there's no way to tell who has what genes. You could easily pair up DomRec with DomRec, and then a quarter of their children would die. A gene like this is very unfortunate, which is why Sickle Cell Anemia is such a problem. However, inbreeding is not the solution. The best solution is for carriers of the Rec gene to outbreed as much as possible in order to avoid other carriers, while still possibly spreading the flu resistance. And yes, if they're carrier's, the best place to find other carriers is in their own family.

Edited September 11, 2012 by MattyG