Is sexual relationship between two consenting adult siblings ethically okay and should it be legal? It’s an interesting ethical problem because there are so many complicated dimensions and it could go either way. I think generally when it comes to social issues our society seems to head in a right direction, people are becoming more tolerant of people who choose differently and so on, but incest between siblings seems to become maybe more taboo even though there are some rational justifications you could make for it.
Some have made parallels to homosexuality as in it doesn’t directly hurt either of the sides of this kind of relationship. There are social problems, I mean if I got to choose I wouldn’t like any of my relatives to get together because that would evoke feelings of disgust, unnecessary drama and awkwardness, but I think I would have said the same thing about homosexuality 70 years ago. In theory inbreeding shouldn’t be a problem, but in practice it probably is. Even though contraception is widespread in this day and age, if large number of siblings have sex with each other, some of them will inevitably end up having kids.
How much can we be sure, if this would be made legal, that the consent of the adult siblings would mean the same thing as the consent of two random unrelated people. If someone wants to have sex with their sibling who is not really happy about that idea, how much opportunity would they have to pressure them into “consent”, if they merely have to wait until their 18th birthday, as opposed to the opportunity to pressure into “consent” someone who is not a relative?
Even if the person who wants to have sex with their sibling waits with the coitus until the sibling’s 18th birthday, they still have plenty of opportunity to “groom” them before they are 18. Imagine siblings with large age difference, where the older sibling uses their mental superiority to “brainwash” their younger sibling, to ruin their other relationships and make them socially isolated, to make them emotionally dependent, so that when the younger sibling becomes 18, they are not in a position to say “no”.
Also, many people at 18 are not really ready to be economically independent on their family. Imagine a family with two children, one strongly loved by the parents, the other disliked by the parents. When the unloved child becomes 18, their sibling can blackmail them into sex by threatening that if they refuse, the popular child will convince the parents to throw the unpopular child out on the street. (Yes, blackmail is technically illegal, but you would have to prove it. Also, if you are the unpopular child, getting the popular child thrown in jail will not help you get your parents’ love; you will still remain on the street.)
In families there is too much power disparity: parents vs children, but also some children vs other. If we care about consent in sex, it is better to not leave open any paths that would allow abusing this power disparity to enforce “consent”. Making sex between close relatives illegal is a simple Schelling point.
In both theory and in practice, it is a problem: the offspring are more likely to have faulty genomes than the offspring of unrelated people.
You could make having offspring illegal. Why must these people have kids? You can get contraception cheaply everywhere nowadays. Does it hurt people more if they can’t have kids, than if it were completely illegal? By making relationships between siblings legal, but making offspring illegal you would appreciate people’s right to self-determination but still take care of the practical issues in some way.
But why are you raising this issue?
Because it’s good ethical practice to try to work out what to do with controversial issues when the answer is not completely clear. There’s a reason why that German ethics council thinks it should be legal.
Because it’s good ethical practice to try to work out what to do with controversial issues when the answer is not completely clear.
I see no visible controversy around the issue.
There’s a reason why that German ethics council thinks it should be legal.
I don’t read German except with more effort than this is worth, although I note that it begins by mentioning a case of a brother and sister having four children together and public consternation over their prison sentence. What reasons does that report give? It is that it considers the German law as it stands an unsatisfactory way to deal with the undesirability of incest, or that society should recognise incestuous relationships as equal to all others? There is a big difference. How does the report propose to handle the negative consequences of inbreeding? Or have you not read any further than ryot.org?
The practical problem is, of course, enforcing this prohibition on procreation. Forced sterilisation is difficult to sell and problematic because the subjects might wish to have children with other people. RISUG might be a solution, once it becomes available.
I’m not sure what I think of the fact that everyone is concerned with the genetics of possible offspring in the case of incest, but nobody minds two chronically depressed, highly neurotic people, one of whom has a hereditary autoimmune condition, procreating… (The domain of quantification for the slightly hyperbolic “everyone” and “nobody” here is the general public rather than LW. I suspect that many in this community would, in fact, mind the latter case as well.)
Is sexual relationship between two consenting adult siblings ethically okay
I think it’s probably like drunk driving—most of the times it doesn’t result in anything bad, but there’s a non-negligible chance of outcomes so bad that the expected value still comes out negative.
should it be legal?
I haven’t given much thought to that, but for some reason your proposed solution of “legal unless you have offspring” sounds more reasonable to my System 1 than the analogous “legal unless you have a crash” in the case of drunk driving.
Or maybe a better analogy would be any driving = any sex between siblings, drunk driving = sex between siblings without contraception? Then again, a law against sex between siblings without contraception doesn’t sound easy to enforce to me.
Enforcing it then would mean castrating at least one of them when they appeal to the authorities for a marriage certificate or something. Doesn’t seem a viable solution.
I think it’s probably like drunk driving—most of the times it doesn’t result in anything bad, but there’s a non-negligible chance of outcomes so bad that the expected value still comes out negative.
Or like drunk driving on your own property, where there is no other traffic nor pedestrians, and you are alone in your car (well, ok, you are in the car with another person, but s/he is drunk as well, knows you are drunk, knows the risks of drunk driving and half of the time replaces you behind the wheel). Should it be illegal? (assuming there are no (health) insurance issues if you crash&injure yourself)
Well, in that case you two cannot affect anyone else but yourselves, whereas in the incest case… Hm, does creating a new person count as affecting them? That’s probably model-dependent… Hm...
Even though contraception is widespread in this day and age, if large number of siblings have sex with each other, some of them will inevitably end up having kids.
A second problem is that the energy and emotions and time they devote to their incestuous relationship isn’t going to a relationship where they might have kids.
5 years ago, I would have thought logically, and said that if they don’t want kids and have access to effective contraception then it isn’t a problem. But now I would think probabilistically, and say that even if they are 99% sure they don’t want kids, they are about 50% likely (assuming standard levels of overconfidance) to change their minds around 30, and now they are really heavily invested in a relationship which cannot lead to healthy kids, and the sister’s biological clock is running out of time.
So, it’s certainly a bad idea, although that doesn’t automatically mean it should be made illegal, depending upon whether you believe citizens should have the right to make bad decisions.
According to wikipedia, 9.4% of gay couples have kids. I dunno what percentage of hetrosexuals have kids, and I dunno what the average age of gay couples is, but it looks like gay couples are a lot less likely to have kids. This is understandable, since people want to raise kids which are related to them.
So yes, my advice would be that bisexuals should only get into hetrosexual relationships, unless they are both ok with sperm banks/adoption. Incidentally, according to some people, the majority of bisexuals are only interested in hetrosexual relationships (and gay sex) although I don’t know whether this is because they want kids someday, or because they are hetroromantic.
From what I’ve heard, the genetic risks have a lot to do with how genetically similar the forebears of the couple are. If all the grandparents are from the same small region, it’s a lot riskier than if the grandparents are from different continents.
I don’t understand why the origin of grandparents should matter.
To the best of my knowledge, the main problem with incest is recessive alleles. For example, if the grandfather’s genotype is ”aA” (where “a” is a very rare recessive allele) and his children (parents’ generation) mate with each other, then there is a relatively high chance (1/16) that the grandchildren would be of “aa” genotype (which might be extremely deleterious or even lethal). Having another grandparent from a different continent should not change this.
There is some reinforcement, but it’s not very significant.
For example, consider an Ashkenazi Tay-Sachs carrier who marries a person from China. If their children mate, the chance that the grandchildren would have Tay-Sachs disease is (1/2)^4=1/16. If instead of a Chinese, this Ashkenazi Tay-Sachs carrier marries another Ashkenazi (who have ~0.03 chance of being a carrier), the chance that the grandchildren would have Tay-Sachs disease is almost the same, ~1/16*1.12. In absence of incest, a grandchild of a Tay-Sachs carrier would have a ~0.03/8 (i.e. ~17 times smaller) chance for getting the disease.
Tay-Sachs allele used to slightly increase evolutionary fitness in heterozygotes (i.e. people who carry just one Tay-Sachs allele). This allowed the allele to increase in frequency until ~3% of Ashkenazis became its carriers. But once the local frequency becomes high enough the negative effects (the risk that a random couple produces children with two Tay-Sachs alleles) balance the positive effects on fitness. Thus in any region it should be impossible for Tay-Sachs to be common for all the grandparents.
Supplemental questions that I don’t know the answers to: how significant are the effects of inbreeding? Are they often so bad that it would be better for an inbred child to never have existed? How does that compare to having non-inbred children with known high risks of genetic defects? To what extent can the effects be tested for (both before and during pregnancy)?
I’d be very surprised if inbreeding was so bad that careful consensual incestuous sex, with the intent of getting an abortion if pregnancy does occur, wasn’t worth the risk.
Edit: Okay, inbreeding seems to be much worse than I’d anticipated.
A sibling-incest child looses 28 IQ points. The risks of all genetic disorders rises massively, from p^2/4 to about p/8, so if the prevalence of carriers of a recessive disease (p) is 1%, then the disease probability would rise by a factor of 50.
That’s almost two standard deviations and looks iffy to me. Yes, I followed the link, the main study resulting in this number is behind the paywall, but I suspect that the sample wasn’t very representative.
Basically, for a sub-population with a recessive trait that leads to mental retardation the outcomes are going to be massively different from the outcomes for a sub-population without such a recessive trait.
I’m impressed she managed to get that big a sample in just Czechoslovakia.
Her sample covers 37 years (1933-1970) and, looking at the sources, she utilized official reports including maternity homes, district courts, etc. so the sample is all Czechoslovakia had officially.
What makes you think there are any human populations none of whose recessive and mutation loads affect cognition?
I don’t think this. Intelligence is strongly polygenic, as far as I know, so for everyone it’s a mix of something good and something bad. But that gene mix is uneven in populations, so some people (low-IQ) get more bad and less good genes, while some people (high-IQ) get more good and less bad.
The thing is, I would expect incest to strongly correlate with very low IQ (your basic drives are still there, but social norms are… less binding). Besides, it’s easier for smarter people to not be caught. So if you select a population which engages in incest (and is detected), you are co-selecting for low IQ and for a larger proportion of bad-for-IQ genes. And the larger that proportion, the worse are the chances (growing superlinearly, too) for the child to have normal IQ.
Do note that in the study sample only 4 females and 2 males among parents attended secondary school, the rest didn’t have any education beyond elementary school (out of 141 mothers and 138 fathers).
Do note that in the study sample only 4 females and 2 males among parents attended secondary school, the rest didn’t have any education beyond elementary school (out of 141 mothers and 138 fathers).
Poor countries are like that. The people in the Indian studies and elsewhere won’t be too highly educated either.
So if you select a population which engages in incest, you are co-selecting for low IQ and so for a larger proportion of bad-for-IQ genes. And the larger that proportion, the worse are the chances (growing superlinearly, too) for the child to have normal IQ.
Shouldn’t affect within-population comparisons… Although since prevalence of cousin-marriage differs drastically from country to country, the inbreeding effect could be driving a nontrivial amount of between-population differences in intelligence. (And of course, it’s not like intelligence is unrelated to national wealth either.)
This is Europe, though, and Communist governments tend to be big on education.
Shouldn’t affect within-population comparisons.
Within which population? The control group involves one parent “from the outside”, so regression to the mean kicks in and the chance of the recessives finding a pair falls dramatically.
I am not arguing that incest has no significant consequences. I am arguing that if you take children of incestuous unions where both parents have reasonable IQ (say, >85), the mean IQ of children would NOT drop by 28 points.
This is Europe, though, and Communist governments tend to be big on education.
It is one of the poorest parts of Europe, and Communist governments tended to be big on a lot of things they couldn’t deliver.
Within which population? The control group involves one parent “from the outside”, so regression to the mean kicks in and the chance of the recessives finding a pair falls dramatically.
If you’re comparing within an Indian population, then the much higher rates of inbreeding aren’t the confound; all you have is the remaining selection effect, and that’s must be small because anything else would drastically contradict the animal and other breeding experiments, and the estimates from genomic methods.
I am arguing that if you take children of incestuous unions where both parents have reasonable IQ (say, >85), the mean IQ of children would NOT drop by 28 points.
It would probably drop by more like 25 points, looking at the weighted averages. (For the surviving children, that is.)
It is one of the poorest parts of Europe, and Communist governments tended to be big on a lot of things they couldn’t deliver.
Communist governments delivered on that one.
Take a look here, specifically pages 21 and 23. The secondary education in Eastern Europe was more prevalent than in Mediterranean countries and Great Britain + Ireland (but less than in Nordic countries and Central Europe). And Czechoslovakia was one of the better Eastern European countries.
If you’re comparing within an Indian population
I went and looked at the Jammu & Kashmir study and it is more convincing than the Czechoslovak study. Hm. It seems my scepticism about the 20+ IQ points drop was unfounded, changing my mind… :-)
But why did my intuition didn’t like the large magnitude of IQ drop? I think because it implies that intelligence is very fragile and very easy to genetically screw up. But if the IQ drop is valid, then intelligence is very fragile. Hmm...
There are two separate questions here. One is: for a given pair of closely related people who very much want to have sex with one another, is doing so (carefully) worth the risk? The other is: should we adjust our societal norms to make things easier for people in that situation?
It seems quite plausible to me that the answers might be “yes, sure” and “heck no”, respectively because, as you say, if lots of siblings or other closely related people have sex then some of them will have children.
Slightly-parallel question: if someone is addicted to heroin and can procure some, should they take it? The answer might be yes, at least some of the time, but we probably still want norms that discourage people from getting addicted in the first place.
(I wonder whether laws and other norms against incest provide some protection against abuse by parents and elder siblings. That shouldn’t be necessary—they should be protected by laws against abuse and against sex with people almost certainly too young for properly informed consent—but maybe there’s some extra deterrent effect.)
Professor Alan Bittles, director for the centre for human genetics in Perth, Australia has collated data on infant mortality in children born within first-cousin marriages from around the world and found that the extra increased risk of death is 1.2%.
In terms of birth defects, he says, the risks rise from about 2% in the general population to 4% when the parents are closely related.
However, cousin marriages might typically be in cultures which accept or promote cousin marriages. This might not work out the same way for pairings from non-cousin marriage cultures.
To be clear, in my heart I feel that I’m against this because for example if people in our family got together it would probably destroy our family. That’s what makes it so interesting because it goes so much against my feelings, but it’s still something that could be right in principle.
That’s about your family’s attitudes, rather than about anything intrinsic to the act.
I would be surprised and possibly grossed out if this happened in my own family, but that would be the moral equivalent of a vistigial limb,* something to get past.
*I was going to say appendix, but the appendix does actually have a function).
Yeah, you’re right. Maybe I didn’t want to admit to myself that this wouldn’t be such a problem if I were thinking purely in consequentialist terms, seeing the disruption of social dynamics and inbred children it would probably cause. However, I actually don’t know how much it would change the amount of sex siblings have, it could be that those who want to do it are already doing it at the moment. “The disruption of social dynamics” argument has been given against homosexuality, but I don’t think it holds weight as much because homosexual relationships resemble more heterosexual relationships than relationships between siblings resemble homosexual relationships.
Is sexual relationship between two consenting adult siblings ethically okay and should it be legal? It’s an interesting ethical problem because there are so many complicated dimensions and it could go either way. I think generally when it comes to social issues our society seems to head in a right direction, people are becoming more tolerant of people who choose differently and so on, but incest between siblings seems to become maybe more taboo even though there are some rational justifications you could make for it.
Some have made parallels to homosexuality as in it doesn’t directly hurt either of the sides of this kind of relationship. There are social problems, I mean if I got to choose I wouldn’t like any of my relatives to get together because that would evoke feelings of disgust, unnecessary drama and awkwardness, but I think I would have said the same thing about homosexuality 70 years ago. In theory inbreeding shouldn’t be a problem, but in practice it probably is. Even though contraception is widespread in this day and age, if large number of siblings have sex with each other, some of them will inevitably end up having kids.
German ethics council decided that it should be legal because it’s a person’s fundamental right and people’s right to self-determination is more important than the protection of your family.
(trigger warning: rape)
How much can we be sure, if this would be made legal, that the consent of the adult siblings would mean the same thing as the consent of two random unrelated people. If someone wants to have sex with their sibling who is not really happy about that idea, how much opportunity would they have to pressure them into “consent”, if they merely have to wait until their 18th birthday, as opposed to the opportunity to pressure into “consent” someone who is not a relative?
Even if the person who wants to have sex with their sibling waits with the coitus until the sibling’s 18th birthday, they still have plenty of opportunity to “groom” them before they are 18. Imagine siblings with large age difference, where the older sibling uses their mental superiority to “brainwash” their younger sibling, to ruin their other relationships and make them socially isolated, to make them emotionally dependent, so that when the younger sibling becomes 18, they are not in a position to say “no”.
Also, many people at 18 are not really ready to be economically independent on their family. Imagine a family with two children, one strongly loved by the parents, the other disliked by the parents. When the unloved child becomes 18, their sibling can blackmail them into sex by threatening that if they refuse, the popular child will convince the parents to throw the unpopular child out on the street. (Yes, blackmail is technically illegal, but you would have to prove it. Also, if you are the unpopular child, getting the popular child thrown in jail will not help you get your parents’ love; you will still remain on the street.)
In families there is too much power disparity: parents vs children, but also some children vs other. If we care about consent in sex, it is better to not leave open any paths that would allow abusing this power disparity to enforce “consent”. Making sex between close relatives illegal is a simple Schelling point.
In both theory and in practice, it is a problem: the offspring are more likely to have faulty genomes than the offspring of unrelated people.
But why are you raising this issue? The practical answer is known, and adequately accounts for the feelings around it.
You could make having offspring illegal. Why must these people have kids? You can get contraception cheaply everywhere nowadays. Does it hurt people more if they can’t have kids, than if it were completely illegal? By making relationships between siblings legal, but making offspring illegal you would appreciate people’s right to self-determination but still take care of the practical issues in some way.
Because it’s good ethical practice to try to work out what to do with controversial issues when the answer is not completely clear. There’s a reason why that German ethics council thinks it should be legal.
I see no visible controversy around the issue.
I don’t read German except with more effort than this is worth, although I note that it begins by mentioning a case of a brother and sister having four children together and public consternation over their prison sentence. What reasons does that report give? It is that it considers the German law as it stands an unsatisfactory way to deal with the undesirability of incest, or that society should recognise incestuous relationships as equal to all others? There is a big difference. How does the report propose to handle the negative consequences of inbreeding? Or have you not read any further than ryot.org?
The practical problem is, of course, enforcing this prohibition on procreation. Forced sterilisation is difficult to sell and problematic because the subjects might wish to have children with other people. RISUG might be a solution, once it becomes available.
I’m not sure what I think of the fact that everyone is concerned with the genetics of possible offspring in the case of incest, but nobody minds two chronically depressed, highly neurotic people, one of whom has a hereditary autoimmune condition, procreating… (The domain of quantification for the slightly hyperbolic “everyone” and “nobody” here is the general public rather than LW. I suspect that many in this community would, in fact, mind the latter case as well.)
Would you then permit homosexual incest, which doesn’t produce children?
I would.
Epistemic status: anally extracted
I think it’s probably like drunk driving—most of the times it doesn’t result in anything bad, but there’s a non-negligible chance of outcomes so bad that the expected value still comes out negative.
I haven’t given much thought to that, but for some reason your proposed solution of “legal unless you have offspring” sounds more reasonable to my System 1 than the analogous “legal unless you have a crash” in the case of drunk driving.
Or maybe a better analogy would be any driving = any sex between siblings, drunk driving = sex between siblings without contraception? Then again, a law against sex between siblings without contraception doesn’t sound easy to enforce to me.
Enforcing it then would mean castrating at least one of them when they appeal to the authorities for a marriage certificate or something. Doesn’t seem a viable solution.
Or like drunk driving on your own property, where there is no other traffic nor pedestrians, and you are alone in your car (well, ok, you are in the car with another person, but s/he is drunk as well, knows you are drunk, knows the risks of drunk driving and half of the time replaces you behind the wheel). Should it be illegal? (assuming there are no (health) insurance issues if you crash&injure yourself)
Well, in that case you two cannot affect anyone else but yourselves, whereas in the incest case… Hm, does creating a new person count as affecting them? That’s probably model-dependent… Hm...
A second problem is that the energy and emotions and time they devote to their incestuous relationship isn’t going to a relationship where they might have kids.
5 years ago, I would have thought logically, and said that if they don’t want kids and have access to effective contraception then it isn’t a problem. But now I would think probabilistically, and say that even if they are 99% sure they don’t want kids, they are about 50% likely (assuming standard levels of overconfidance) to change their minds around 30, and now they are really heavily invested in a relationship which cannot lead to healthy kids, and the sister’s biological clock is running out of time.
So, it’s certainly a bad idea, although that doesn’t automatically mean it should be made illegal, depending upon whether you believe citizens should have the right to make bad decisions.
The same reasoning would suggest that bisexuals should only get into same-sex relationships. Would you say that as well?
I disagree with the idea that they can’t have kids. They can adopt. The girl can go to a sperm bank.
They can adopt kids, yes.
According to wikipedia, 9.4% of gay couples have kids. I dunno what percentage of hetrosexuals have kids, and I dunno what the average age of gay couples is, but it looks like gay couples are a lot less likely to have kids. This is understandable, since people want to raise kids which are related to them.
So yes, my advice would be that bisexuals should only get into hetrosexual relationships, unless they are both ok with sperm banks/adoption. Incidentally, according to some people, the majority of bisexuals are only interested in hetrosexual relationships (and gay sex) although I don’t know whether this is because they want kids someday, or because they are hetroromantic.
From what I’ve heard, the genetic risks have a lot to do with how genetically similar the forebears of the couple are. If all the grandparents are from the same small region, it’s a lot riskier than if the grandparents are from different continents.
I don’t understand why the origin of grandparents should matter.
To the best of my knowledge, the main problem with incest is recessive alleles. For example, if the grandfather’s genotype is ”aA” (where “a” is a very rare recessive allele) and his children (parents’ generation) mate with each other, then there is a relatively high chance (1/16) that the grandchildren would be of “aa” genotype (which might be extremely deleterious or even lethal). Having another grandparent from a different continent should not change this.
Why wouldn’t having grandparents from different continents make rare alleles less likely to be reinforced?
There is some reinforcement, but it’s not very significant.
For example, consider an Ashkenazi Tay-Sachs carrier who marries a person from China. If their children mate, the chance that the grandchildren would have Tay-Sachs disease is (1/2)^4=1/16. If instead of a Chinese, this Ashkenazi Tay-Sachs carrier marries another Ashkenazi (who have ~0.03 chance of being a carrier), the chance that the grandchildren would have Tay-Sachs disease is almost the same, ~1/16*1.12. In absence of incest, a grandchild of a Tay-Sachs carrier would have a ~0.03/8 (i.e. ~17 times smaller) chance for getting the disease.
Ashkenazi Jews is too large a category. Try Ashkenazi Jews from a region where Tay Sachs is common for all the grandparents.
I don’t think this is possible.
Tay-Sachs allele used to slightly increase evolutionary fitness in heterozygotes (i.e. people who carry just one Tay-Sachs allele). This allowed the allele to increase in frequency until ~3% of Ashkenazis became its carriers. But once the local frequency becomes high enough the negative effects (the risk that a random couple produces children with two Tay-Sachs alleles) balance the positive effects on fitness. Thus in any region it should be impossible for Tay-Sachs to be common for all the grandparents.
I think this is true, but its pretty risky even in the best case.
Supplemental questions that I don’t know the answers to: how significant are the effects of inbreeding? Are they often so bad that it would be better for an inbred child to never have existed? How does that compare to having non-inbred children with known high risks of genetic defects? To what extent can the effects be tested for (both before and during pregnancy)?
I’d be very surprised if inbreeding was so bad that careful consensual incestuous sex, with the intent of getting an abortion if pregnancy does occur, wasn’t worth the risk.
Edit: Okay, inbreeding seems to be much worse than I’d anticipated.
According to this:
http://dare.uva.nl/cgi/arno/show.cgi?fid=152307
A sibling-incest child looses 28 IQ points. The risks of all genetic disorders rises massively, from p^2/4 to about p/8, so if the prevalence of carriers of a recessive disease (p) is 1%, then the disease probability would rise by a factor of 50.
That’s almost two standard deviations and looks iffy to me. Yes, I followed the link, the main study resulting in this number is behind the paywall, but I suspect that the sample wasn’t very representative.
Basically, for a sub-population with a recessive trait that leads to mental retardation the outcomes are going to be massively different from the outcomes for a sub-population without such a recessive trait.
Available the usual places: https://www.dropbox.com/s/8gv0el0anfyymed/1971-seemanova.pdf / http://moscow.sci-hub.bz/092ee3d082e9cffd04b7064c36ba808a/10.1159%40000152391.pdf (Personally, I’m impressed she managed to get that big a sample in just Czechoslovakia. Creepy. Also, note that’s only one of the studies being meta-analyzed.)
It’s very clear that inbreeding is really bad: to give some examples, it drives species extinct within generations, its effects are long-term and underestimated, inbreeding can result in 20+ IQ points loss in other populations such as in India and of course we all know about the Habsburgs (which was so extreme that “Charles II was moderately more inbred than the average among the offspring from brother-sister matings”).
What makes you think there are any human populations none of whose recessive and mutation loads affect cognition?
Her sample covers 37 years (1933-1970) and, looking at the sources, she utilized official reports including maternity homes, district courts, etc. so the sample is all Czechoslovakia had officially.
I don’t think this. Intelligence is strongly polygenic, as far as I know, so for everyone it’s a mix of something good and something bad. But that gene mix is uneven in populations, so some people (low-IQ) get more bad and less good genes, while some people (high-IQ) get more good and less bad.
The thing is, I would expect incest to strongly correlate with very low IQ (your basic drives are still there, but social norms are… less binding). Besides, it’s easier for smarter people to not be caught. So if you select a population which engages in incest (and is detected), you are co-selecting for low IQ and for a larger proportion of bad-for-IQ genes. And the larger that proportion, the worse are the chances (growing superlinearly, too) for the child to have normal IQ.
Do note that in the study sample only 4 females and 2 males among parents attended secondary school, the rest didn’t have any education beyond elementary school (out of 141 mothers and 138 fathers).
P.S. Thanks for the link to the study.
Poor countries are like that. The people in the Indian studies and elsewhere won’t be too highly educated either.
Shouldn’t affect within-population comparisons… Although since prevalence of cousin-marriage differs drastically from country to country, the inbreeding effect could be driving a nontrivial amount of between-population differences in intelligence. (And of course, it’s not like intelligence is unrelated to national wealth either.)
This is Europe, though, and Communist governments tend to be big on education.
Within which population? The control group involves one parent “from the outside”, so regression to the mean kicks in and the chance of the recessives finding a pair falls dramatically.
I am not arguing that incest has no significant consequences. I am arguing that if you take children of incestuous unions where both parents have reasonable IQ (say, >85), the mean IQ of children would NOT drop by 28 points.
It is one of the poorest parts of Europe, and Communist governments tended to be big on a lot of things they couldn’t deliver.
If you’re comparing within an Indian population, then the much higher rates of inbreeding aren’t the confound; all you have is the remaining selection effect, and that’s must be small because anything else would drastically contradict the animal and other breeding experiments, and the estimates from genomic methods.
It would probably drop by more like 25 points, looking at the weighted averages. (For the surviving children, that is.)
Communist governments delivered on that one.
Take a look here, specifically pages 21 and 23. The secondary education in Eastern Europe was more prevalent than in Mediterranean countries and Great Britain + Ireland (but less than in Nordic countries and Central Europe). And Czechoslovakia was one of the better Eastern European countries.
I went and looked at the Jammu & Kashmir study and it is more convincing than the Czechoslovak study. Hm. It seems my scepticism about the 20+ IQ points drop was unfounded, changing my mind… :-)
But why did my intuition didn’t like the large magnitude of IQ drop? I think because it implies that intelligence is very fragile and very easy to genetically screw up. But if the IQ drop is valid, then intelligence is very fragile. Hmm...
There are two separate questions here. One is: for a given pair of closely related people who very much want to have sex with one another, is doing so (carefully) worth the risk? The other is: should we adjust our societal norms to make things easier for people in that situation?
It seems quite plausible to me that the answers might be “yes, sure” and “heck no”, respectively because, as you say, if lots of siblings or other closely related people have sex then some of them will have children.
Slightly-parallel question: if someone is addicted to heroin and can procure some, should they take it? The answer might be yes, at least some of the time, but we probably still want norms that discourage people from getting addicted in the first place.
(I wonder whether laws and other norms against incest provide some protection against abuse by parents and elder siblings. That shouldn’t be necessary—they should be protected by laws against abuse and against sex with people almost certainly too young for properly informed consent—but maybe there’s some extra deterrent effect.)
http://news.bbc.co.uk/2/hi/health/7404730.stm
However, cousin marriages might typically be in cultures which accept or promote cousin marriages. This might not work out the same way for pairings from non-cousin marriage cultures.
I made comments to a similar effect in a recent OT http://lesswrong.com/lw/mgr/open_thread_jul_13_jul_19_2015/ckh8 :)
To be clear, in my heart I feel that I’m against this because for example if people in our family got together it would probably destroy our family. That’s what makes it so interesting because it goes so much against my feelings, but it’s still something that could be right in principle.
I wouldn’t go so far as saying it is “right” but certainly “harmless” in principle, once you remove procreation from the equation.
That’s about your family’s attitudes, rather than about anything intrinsic to the act.
I would be surprised and possibly grossed out if this happened in my own family, but that would be the moral equivalent of a vistigial limb,* something to get past.
*I was going to say appendix, but the appendix does actually have a function).
Dude, be a consequentialist. Don’t use expressions like “ethically okay” or “morally wrong”. Use “superior to”, “inferior to”.
Is the imperative mood the new way to convince people of an ethical theory on LessWrong these days, or something?
Yeah, you’re right. Maybe I didn’t want to admit to myself that this wouldn’t be such a problem if I were thinking purely in consequentialist terms, seeing the disruption of social dynamics and inbred children it would probably cause. However, I actually don’t know how much it would change the amount of sex siblings have, it could be that those who want to do it are already doing it at the moment. “The disruption of social dynamics” argument has been given against homosexuality, but I don’t think it holds weight as much because homosexual relationships resemble more heterosexual relationships than relationships between siblings resemble homosexual relationships.