Should Incest be Decriminalised? (Part Two)

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Image from Game of Thrones (HBO/G.RR. Martin), which depicts an
incestuous relationship between twins Jaime and Cersei

(Part One)

This post is the second in a brief series looking at the topic of incest. Now, if ever there were a topic that was apt to appeal to the “yuck”-factor in ethics, this is it. But this series is trying to set aside this instinctive feeling of disgust and take a sober look at the arguments typically offered in favour of criminalising incestuous relationships. To this end, I’m making heavy use of Vera Bergelson’s article “Vice is Nice but Incest is Best” which examines five traditional rationales for criminalisation.

In part one, I did two things. First, I set out the basic contours of the debate, defining “decriminalisation” as the removal of punitive sanction from an activity or set of activities, and “criminalisation” as the application of punitive sanction. I noted that, under these definitions, it was possible to argue for the decriminalisation of incest, without thereby arguing for its social acceptability or encouragement. Still, I recognised that there might be some slippery slope arguments to the contrary. I also distinguished between paradigmatic (sibling-sibling/parent-child) and non-paradigmatic (e.g. uncle-niece) cases of incest, arguing that the former were probably more testing than the latter. Nevertheless, I noted that most incest statutes cover non-paradigmatic cases, as well as paradigmatic ones, and so any analysis of the decriminalisation of incest must bear them in mind too.

The second thing I did in part one was to examine two arguments that allegedly support the criminalisation of incest. They were the argument from religious authority and the argument from universal tradition. Both arguments were found to be somewhat lacking, offering at best explanations for why incest has been criminalised, not justifications for its criminalisation.

In today’s post, I look at two rather more significant pro-criminalisation arguments. The first, and probably most significant, is the argument from genetic defectiveness. The second is the argument from the protection of the family unit. Both have some secular appeal, but both are problematic. As we shall see.


1. The Argument from Genetic Defectiveness
That the offspring generated by incestuous procreation have an increased risk of carrying genetic defects, is often cited as a reason against them. The claim can be supported with some simple Mendelian principles. As anyone who has taken a basic intro to biology course will know, the human genotype is made up of chromosomal pairings of genes. One half taken from one parent, the other half taken from the other parent. The phenotypical expression of a trait depends on which pairings one has, specifically whether the pairings consist of dominant or recessive genes and in what mix.

Take a simple trait like eye colour. Brown eye colour is a dominant trait (the gene for this will be denoted by “B”); blue eye colour is recessive (the gene for will be denoted with a “b”). The vagaries of phenotypic expression are such that if there is at least one brown eye gene present in your inherited pairings (i.e. if you have BB, bB, or Bb pairings), you will have brown eyes. Only if you have two of the blue eye genes (i.e. bb) will you have blue eyes. So if your parents are both have the BB genotype, you will definitely have brown eyes; if they both have the Bb genotype, there is a one in four chance that you will have blue eyes; and if they both have the bb genotype, you will definitely have blue eyes.

Most recessive genetic traits are benign — like having blue eyes, which might arguably be an advantage — but some are not. These we call deleterious recessive traits. The problem with incestuous procreation is that it increases the probability of recessive traits being expressed in the offspring, because its more likely that the parents have heterozygous (dominant-recessive) or homozygous (recessive-recessive) gene pairings. If these recessive traits are deleterious, this could have seriously harmful consequences for the resultant offspring. And so there is good reason to criminalise incest. Or so the argument goes.

We can put it like this:

• (1) If activity X is likely to lead to the creation of genetically defective offspring, X should be criminalised. 

• (2) Incest is likely to lead to the creation of genetically defective offspring. 

• (3) Therefore, incest should be criminalised.

One general comment about this argument is in order. The principle — premise (1) — is expressed in a somewhat unnatural way. In particular, references to some variable “activity X” seem odd given that there is really only one type of activity in mind when we think of creating offspring. However, there is a reason for the somewhat unnatural construction, and it should become clear as we move on to evaluate the argument, which is what we are now going to do.


2. Evaluating the Argument from Genetic Defectiveness
Superficially, the argument from genetic defectiveness has some appeal. The principle can be supported by typical harm avoidance grounds that are popular in criminalisation debates. It is generally thought that an activity that harms others can be justifiably criminalised. Arguably, genetically defective offspring are harmed by their defects, so the activities that lead to their creation can be prohibited on the basis that they are harmful.

As I say, this has some superficial appeal, but on closer inspection the principle here seems dubious, highly dubious. As Bergelson points out, there are many other sexual unions that are likely to lead to genetically defective offspring, but which we wouldn’t dream of subjecting to criminal sanction. The language of “defectiveness” is going to be inflammatory here, so let’s be clear that by this we mean a recessive trait that when expressed is thought to disable or impair one of the major life functions. Examples of sexual unions that are likely to lead to such offspring, but which we wouldn’t dream of criminalising include those between deaf-mute and dwarf partnerships (the latter being possibly controversial). Further, if this principle were correct, given modern gene sequencing technologies, we should probably demand genetic screening of all procreative partnerships and ban those most likely to lead to defective offspring. But that would seem to be an unpleasant notion, far too close to early 20th century eugenics for comfort. So premise (1) looks doubtful. Since I’m going to construct an map for this particular argument I’ll summarise this line of reasoning in a numbered premise:

• (4) There are many sexual unions that are likely to lead to genetically “defective” offspring that are not apt for criminalisation.

So much for premise (1), what about premise (2)? Evaluating this premise is where the ambiguity of the phrase “activity X” comes into play. To claim that incest is likely to lead to genetically defective offspring is to trade on the vague nature of the term “incest”. It is really only uncontracepted vaginal intercourse that is covered by premise (1); and yet “incest” could involve other activities which are disconnected from procreation. As noted in part one, English law on incest bans all penetrative sexual acts between a certain class of relatives, which includes non-procreative acts. Other laws in other countries cover non-penetrative acts and marriage, none of which are inclined to lead to procreation. So premise (2) is false if the term “incest” is understood in its broadest sense.

• (5) The term “incest” covers non-procreative acts as well as procreative ones. Under the logic of this argument, the non-procreative activities should be decriminalised.

But even if the argument is corrected, and “incest” is understood in the narrower sense, there is some doubt as to the truth of premise (2). Bergelson claims (without supporting the claim) that the number of defects associated with inbreeding is relatively low. Make of that what you will; I’m in no position to evaluate it properly. She also adopts an interesting argument made by Carolyn Bratt in the mid-1980s which claimed that banning incestuous procreation might actually exacerbate the problem of deleterious recessive traits.

Bratt’s reasoning was that if a recessive trait is sufficiently deleterious, then it is more likely to be filtered out of the population if we allow incestuous procreation than if we don’t. Sufficiently deleterious traits are likely to lead to death or infertility when expressed in homozygous individuals. But homozygous individuals are more likely to result from incestuous unions. In a sense then, the deleterious genetic line is more likely to come to an end through an incestuous union. So far the argument follows the logic of the pro-criminalisation one. The difference comes in the next step. If incestuous unions are banned, then the recessive trait in question is more likely to disperse through the population. This would be thanks to the creation of more and more heterozygous progeny, all carrying the recessive trait but not expressing it. But if there are more and more heterozygous people carrying the trait, then the risk of future homozygous progeny goes up. Thus, although banning incestuous procreation may prevent harm to the next generation, it creates downstream problems.

• (6) Bergelson’s claim: there are relatively few serious defects associated with inbreeding.

• (7) Bratt’s argument: banning incestuous procreation may lead to the more widespread dispersal of deleterious recessive traits through the population.

Now, I’m somewhat unconvinced by Bratt’s argument. This is for two reasons. The first is that incestuous procreation is not going to be the norm even if it is decriminalised (for deep-seated psychological reasons), so the reduced-dispersion effect that Bratt alludes to is unlikely to be that significant. The second is that there is a dubious consequentialist logic to this argument. It suggests it might be okay to sacrifice one generation in the interests of other future generations. But these kinds of population-based, future generations arguments can lead to repugnant conclusions, as many others have pointed out. Still, the argument may succeed in making us realise that considerations of genetic defectiveness are more complex than we first realised and that may be sufficient to lessen the appeal of the argument from genetic defectiveness.

Click to enlarge

3. The Argument from Family Protection
A different argument for the criminalisation of incest derives from the value of familial stability. The reasoning is fairly elementary. The family unit (in its so-called “nuclear” form) is an important social institution, both for the role it plays in perpetuating society and for the role it plays in the socialisation and education of children. Anything that would damage the stability of the family unit would be bad. Incestuous relationships would destabilise the family unit either because they would lead to sexual jealousies and rivalries in the family, or because they would undermine parental role models that prepare the young for the future assumption of familial responsibilities.

To state this argument more formally:

• (8) If an activity would damage the stability of the family unit, it ought to be criminalised. 

• (9) Incest would damage the stability of the family unit.  

• (9.1) Incest would lead to sexual jealousies and rivalries within the family. 

• (9.2) Incest would undermine good parental role models. 

• (10) Therefore, incest ought to be criminalised. 

Interestingly enough, as Bergelson points out, this argument was thought to provide the most persuasive reason for criminalising incest by the drafters of the Model Penal Code, which is a model set of criminal laws that has been influential in shaping the content of the criminal statutes in many US states. But despite garnering the imprimatur of the MPC, the argument is surprisingly weak.

The first issue is that the principle — premise (8) — is too broad. Are we really saying that everything that damages the stability of the family unit ought to be criminalised? Perhaps conservatives think so, but this would include a surprisingly long list of activities. Even if we limit ourselves to just the forms of jealousy that might undermine familial stability, we might find reason to criminalise activities other than incest. Siblings often compete with each other for affection and attention within the family, and for accolades outside. Oftentimes, these competitions can become bitter and all-consuming. Should we try to ban those too? It seems implausible to suggest that we should, yet this is what the principle demands.

The factual claim — premise (9) — is also problematic. Bergelson argues that there are at least some types of incestuous relationship that would not create sexual jealousies and rivalries. For instance, sister-sister and mother-daughter relationships are unlikely to create sexual rivalries. Also, many famous incest cases involve siblings who were raised in separate families, reunited as adults, and began an incestuous relationship that followed the typical nuclear family form. Should they not be permitted since they do not lead to the destabilising effects mentioned?

Okay, I’ll leave it there for now. In the next post we’ll look at two more arguments. One of which claims that incest bans help to prevent intra-familial abuse, the other of which claims that the law should enforce moral taboos.