In these cases, the truly consensual case of incest (and if you delve into the facts of the German case, it isn’t obvious that the German case is one of them), are likely to be few and far between and the procedural utility of not having to show exploitation in a context where it may be hard to prove something that is really present may outweigh the downside of a few prohibited relationships that don’t deserve to be prohibited on the basis of lack of true consent and exploitation.

When you start with that premise, then second order considerations, like genetic risk, can fairly inform the question of whether it really makes sense to make exceptions for the rare cases that might be O.K. from a consent/exploitation analysis. If even the “pure consensual” cases still have downsides and are rare anyway, the utility of a simpler, less case specific incest ban is even greater.

It is also worth considering that the Germans imposed a sentence (three years) much milder than what many U.S. states would impose on teachers and students who are both adults in a much more likely to be consensual relationship who have sex and don’t have kids and have no genetic risk. The punishment may be pretty mild in this case because the act, while deviant, isn’t considered as horrible as other acts of incest.

http://www.hollandbloorview.ca/bloom/rh_happy_children_disability_not.html

http://bloom-parentingkidswithdisabilities.blogspot.ca/2011/12/costs-quality-of-life-assumptions-put.html

http://bloom-parentingkidswithdisabilities.blogspot.ca/2012/01/disability-paradox.html

I don’t believe that genetic defects are the prime reason for the societal taboo on sibling incest.

If you feel we should ban the marriage of people carrying the Tay Sachs genes, where would you lift the ban when a disability is detected prenatally? Should I be ‘allowed’ to carry a child with Down syndrome to term? What about a child with only a physical disability? What about a child who is deaf?

Does it matter how these real people rate their quality of life? Does it matter how their families rate their contributions?

Maybe we should start banning the birth of any societally marginalized group — separate from disability. Forget about changing prejudice — let’s just keep it alive in a vacuum of homogeneity.

For someone who calls himself a scientist, you throw around the word ‘retarded’ an awful lot. Is that a word you use in your academic papers?

I did a little analysis of selfing plants. You can reach almost universal homozygosity in just 5 generations.

Inbreeding Is Screwing Yourself

Too bad most active hobby breeders (and occasional totalitarian regimes) aren’t satisfied keeping their genetic meddling and ideas of genetic purity to plants, a life-form which we ascribe very little moral implications to. There’s arguably little harm done by entertaining genetic failures of flowering plants in search of a ribbon winning paeony, although large scale mono-cultures are not as easy to write off as benign.

But society doesn’t generally have such a favorable view of producing dysfunctional sentient beings. I expect more from a cow than I do some corn, more from a dog than I do a cow, and more from a child than I do a dog. And the level of ethics of how those things are bred rises too. Few people care about monoculture plants. There is little stigma of eating an inbred cow (although the practical nature of hybrid vigor makes $ driven cattlemen more likely to outcross than many in dogs who count “breeds” as sacred and unchanging even though most are fewer than 100 years old). There is growing backlash against hard core eugenicist dog breeding methods with greater public awareness.

Close human inbreeding is generally looked down upon and the communities that embrace it do so with rather suspect motives: racism, culturism, isolationism, etc. And in any one you can name (be it Arab immigrants in the UK or religious sects in Utah) we see rising levels of disease and often novel deleterious mutations.

> if the couple have a lot of particularly good recessive genes then…

By the very nature of being recessive most alleles are actually broken and are non-functional. Novelty might make these phenotypes seem desirable, such as with loss of pigment recessives (we see this all the time in dog breeding where recessive coat colors are fetishized). But these are hardly “good” save for that novelty.

Recessive Means Broken

> If first degree relatives are free of all known deleterious genes and have a lot of good heritable qualities then one could even make an argument for encouraging them to breed.

Yet another spurious argument we see so often in pure bred dog breeding circles. The notion of “free of all known deleterious…” There are several rather simple refutations of this argument.

(1) We know so little about disease genetics, we are very much in a state of ignorance. So being free from “all known” deleterious recessives isn’t actually saying very much.

Only a small fraction of diseases are even mapped to genetic tests and even the definition of what a disease is and “a gene for disease X” are controversial ideas. Just because we have developed mental models of “genetic disease” and “genes that cause disease” does not mean that most disease paths are so easy to differentiate from the wildtype “normal” biological processes.

The Limits of “Health” Testing
and
You Can’t Pass a Health Test You Don’t Take
cover this issue in dog breeding where eugenics is as alive today as it was in the 30s and 40s.

(2) If you should find a stud that is free from deleterious recessives, is it not better to use him to create clear phenotypes and carrier/clear genotypes in lines that are affected? I.e. slowly weeding out disease over many generations without a rush to cut out “bad” genes and thus lose genetic diversity in a small gene pool? This isn’t as much of an issue when the gene pools are large and there are many breeders, but it is very much an issue in dogs where artificial segregation into rigid and closed breeds highlights the damage done by loss of diversity.

(3) New mutations happen all the time. Genetic drift sends most of them into history without ever being expressed, so why would you want to take that risk by breeding seemingly clear close relatives when doing so is really the only way most of these brand new mutations are ever going to become homozygous?

For example, something like 80%+ cases of achondroplasia in humans are due to de novo mutations, i.e. no known family history of the mutation. The mutation which causes this is likely at a fragile location that is PRONE to mutate. Breeding “healthy” close relatives brings these sorts of diseases to light.

That’s why you often see novel “diseases” in inbred human populations. Those mutations would likely never have doubled up had inbreeding not been in place. And, once you have an incubator community for new deleterious recessives and then these breeders are released into the world, you have a situation where you’ve greatly magnified the chance that such genes will move toward becoming fixed in a population versus lost due to drift.

I saw somewhere (John Hawks?) something to the effect that since the beginning of civilization societies have executed an average of 10% of each generation and it’s only in recent centuries this has declined.

That is, for the most part, the most violent or disruptive 10% of each generation has been systematically eliminated. Is this not eugenics?

And hasn’t it been established that women, given the choice tend to go for the guy with the most different immune system and that objections to incest have to do with ensuring the broadest level of immune system coverage in a population?

don’t ever use quotes like that again or i’ll ban you. i didn’t use the word improvement, probably because i reject your characterization of my argument (in contrast, i did use logic, so i accept the usage of quotes in response to me there). instead of making your own position clear, you keep setting up my own position for your own trivial but true or non-trivial but opaque rebuttals.

As for “nature being nature”– my point is that it seems pretty arrogant to think that the application of “logic” in passing to a system that is as complex as a human society can readily come up with an “improvement.”

As for my facts, I’d be very interested in hearing what you think is false…

Do you really believe your own answer to this question? If any genetic mutation comes along and improves reproductive success, how long will it be before the people without the mutation are considered “freaks?”

of course i believe it. i’m talking in a proximate sense as who i am now. if you have a biological background you are aware that something like ‘reproductive success’ is very ambiguous in the long term, so my ‘thought experiment’ obviously wasn’t realistic. i really don’t think you’re even address me, or, you want me to address a different set of questions. as i stated above, nature is nature. it’s not useful for me to consider that eusocial WASPs would consider humans freaks.

Actually no– I’m not arguing slippery slope. I’m questioning your premise that you’ve somehow figured out something that society hasn’t.

*Any* curtailment of reproduction (be it, incest, norms banning pre-marital sex, or whatever) inherently involves a lot of work for society to impose its values on individuals.

The question then becomes what values society chooses to impose. Some values (like repulsion to incest) appear to be hard-wired into humans and society can get broad agreement on the use of force. Other values— like insuring care for the young– appear to be so fundamental to advanced societies that institutions like marriage are nearly universal. Still other values– like ensuring paternal lineage– are much less universal but still find expression in practices like clitorectomy, chastity belts, and social norms against female sexuality.

It would seem that different societies’ willingness to impose these sorts of values reflects the benefits of the imposition. In other words, it is really important that incest not occur, it is slightly less important that parents care for their children, and it is somewhat important that the cuckoldry rate be kept pretty small.

In your own example of Tay-Sachs– there seems to be broad agreement that the benefits of allowing couples to marry whom they want, control their own reproductive behavior, maintain their pro-life beliefs, whatever– outweigh the benefits of infants and toddlers dying miserable deaths. You disagree and propose to “think logically” about this situation.

The heart of my position is that although it is possible that society is wrong and that there’d be some great– previously unknown– benefit to your proposal, I believe that chances are that society kinda knows what its doing. In other words, you bear the burden of proof that the sort of restrictions you propose would actually be beneficial.

Turning to your question:
if there was a mutation which turned people into fast breeding spiders which were totally mindless and expired within a few years, who’s actually a freak? THEY ARE FREAKS!

Do you really believe your own answer to this question? If any genetic mutation comes along and improves reproductive success, how long will it be before the people without the mutation are considered “freaks?”

on a deep level everything is an evolutionary psychological accident. i take your point, but a lot of the rational thinking is a waste of time for almost everyone.

In addition to what others have said, there is a very important difference that no one has yet mentioned, and it comes up often in discussions of euthanasia. In most cases (i.e. with adults), those who are disabled and who find their lives no longer worth living are able to make this decision for themselves. It is their choice and their right. It is only in the case of those who cannot decide for themselves (e.g. infants) that we make decisions for them.

Razib said:
…we would save a lot of time wondering whether bestiality is rape due to issues of animal consent if we just went with our first instincts and agreed that normal people don’t prefer sex with animals to sex with conspecifics…

Yes but what if our first instincts aren’t very good? Or what if what most people consider “normal” is simply a result of cultural or even evolutionary psychological accident? How do we know we aren’t foisting our biases on humans with outlier psychologies for a bad reason? The only way to know, I think, would be to think about it rationally.

If “what most people think” is a practical limit to rationality, I think that’s a limit we’re better off breaking through.

This is utter nonsense. We prevent children from being born all the time for all sorts of reasons, and no one has a problem with it. If my mother had been in a bad mood on a certain critical night this would have prevented me from ever being born. So what? Most likely someone else would have been conceived on a different night, someone who doesn’t exist precisely because I do exist. And in any case the world would move on. There is simply no problem here.

The thing is, there is a huge difference between a potential person — a person who might exist, but doesn’t exist yet — and an actual person. Potential people are ephemeral, they exist in huge numbers, and most never actually come to exist. There is no conceivable way you can extend any sort of rights to them. At least at the earliest stages a fetus has no mind, so there is no person there, even though a body does exist. Deciding you don’t want to bring that fetus to term has no more moral weight than deciding you don’t want to have unprotected sex on a particular night. In both cases you are simply deciding the fate of potential people, not actual people.

Since you’re a fan of slippery slopes, I should say that if there’s no functional difference between executing someone disabled and never allowing them to be born, that means it’s fundamentally wrong to prevent the creation of any human being. Hence the Mormons are right, and we should have as many children as physically possible, as otherwise we are denying potential human beings existence. Hell, we should expand the global population to hundreds of billions and convert the entire biosphere to either be human or food for humans.