Sunday School: On Kissing Cousins


Skeptics and atheists almost universally support marriage equality across genders, and increasingly independent of number and exclusivity. Lately i’ve read advocacy for *full* marriage equality, including for close relatives (consanguineous relationships). The only reasonable objections i’ve ever heard have to do with the increased risk of disorders and immunodeficiency. However, i’m not versed in the scientific / medical literature, and unless the risk is extreme it seems more appropriate to educate rather than stigmatize (as with teen pregnancy).

So, what should we bear in mind about consanguinamory? Where can we find reliable information (esp. for our large and geographically mobile population)? What should we learn before becoming consanguineous allies? –C.

Well, that’s a question you don’t see every day.

Although I have a fairly strong background in science, I am much better versed in chemistry and physics as opposed to life sciences. So I asked somebody else about the biological end, to enhance our collective understanding.

“Essentially, yes, there is a certain amount of risk in consanguineous breeding,” answered Leslie Kendall, a graduate researcher in genetics at Texas A&M University. “Genetic testing can mitigate some of this as far as well established genetic disorders, but you have to remember that not everything is testable, so even if these parents had clear tests, there is the possibility of something popping up (a greater chance than from non-consanguineous breeding). It depends solely upon what they are bringing to the party.” For a more thorough entry-level explanation, she recommends this very illuminating 2003 Discover article.

Given that cousin marriage is pretty widespread and has been through the majority of human history, and that as a species we seem to have done just fine–albeit with some pretty high-profile outlying exceptions, like the Tsarevich Alexei–rejecting it on a biological basis is illogical. Even an isolated close-relative coupling (half-siblings or closer, as expressed by a mathematical coefficient of inbreeding F) within an otherwise robustly branched family tree is unlikely to have serious deleterious effects, so long as the partners aren’t carriers for a marquee genetic disorder like hemophilia or Tay-Sachs, both of which are testable.

Cultural stigmas surrounding incest, however, can’t really be dismissed with straightforward math in the same way. Ultimately I believe that consenting adults have a right to whatever bedroom activities tickle their individual fancies, so long as they exercise some minimum amount of due diligence to ensure that nobody’s getting hurt in a way they didn’t ask for. Healthy, satisfying relationships between individual persons are good for all of us in aggregate. If a couple experiences genetic sexual attraction, for example, there is no rational reason to treat them differently than any other couple. Much of the discourse on incest centers on abuse, and rightly so, but a marriage between adult siblings doesn’t normalize sexual abuse between minor siblings or a parent and minor child any more than a marriage between two men normalizes the sexual abuse of a boy by an adult man. It turns out the feminists were right–everything centers on consent.

In a fairly stunning coincidence, while I was working on this column, Dear Prudence on Slate ran a letter from half of a consensually incestuous gay couple that basically said exactly what I would have said, except better. I definitely would refer readers to Emily Yoffe’s answer. She appears to be a pretty good model for consanguineous allies!

If you would like to submit a question to Sunday School, please use our contact form. We won’t publish your real name (unless you want us to), and creative pseudonyms get bonus points!

Featured image from Harry Potter and the Order of the Phoenix, 2007. Also, you can follow Leslie Kendall, who is totally rad, on Twitter here.

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  1. I speculate that a lot of the stigma around incest has to do with the Westermarck effect. The idea is that incest is evolutionarily unfavorable, and thus people evolved a psychological mechanism to prevent attraction to relatives. The mechanism uses “people you grew up with” as a proxy for “close relatives”. Thus, people sometimes become attracted to close relatives that they did not grow up with. And other people must simply not experience the Westermarck effect.

    When people think of incest, they think about how averse or unattracted they are by the prospect of getting with their own close relatives. If enough people think this way, it can lead to a powerful cultural taboo. I consider the health risks to be an after-the-fact justification (not that there is no truth to it).

    Of course, I don’t study evolution or psychology, and don’t have the expertise to evaluate the truth of my speculation.

  2. Thank you for those resources, the Discover article in particular! For anyone who doesn’t read it, i found this passage especially enlightening:

    “The consequences of inbreeding are unpredictable and depend largely on what biologists call the founder effect: If the founding couple pass on a large number of lethal recessives, . . . these recessives will spread and double up through intermarriage. If [not], their descendants could safely intermarry for generations—at least until small deleterious effects inevitably began to pile up and produce inbreeding depression, a long-term decline in the well-being of a family or a species.”

    There are risks, as in any sexual or childrearing relationship, and these, it seems, are mundanely minimal and can be reliably assessed. I clearly have more to learn, but i am ready to be a consanguinamorous ally.

  3. You’re right that full marriage equality would involve abolishing anti-incest laws, though I think that you’ve taken the wrong approach in arguing that position.

    Sure, consanguineous matings have a higher chance of producing birth defects or other genetic abnormalities, but that should have no bearing whatsoever on whether or not a particular marriage is recognized by the law. Tons of people are genetically predisposed to having offspring with developmental abnormalities. Huntington’s Disease is a dominant trait… half of the children born to an individual with Huntington’s will develop this terrible neurodegenerative condition that causes them to die young. Certain types of colorectal cancer are caused by dominant mutations. Women over the age of 35 have a hugely increased risk of having children with chromosomal aberrations like Down syndrome. Should we forbid people with Huntington’s, colon cancer, or women over the age of 35, from getting married? Absolutely not. I think that it follows that the potential “genetic fitness” of one’s offspring should have no bearing on whether you can get married or not.

    • I’m glad to see this distinction made, and i agree that it is the correct position when it comes to marriage rights.

      The question can be broadened in scope: Should we actively work toward deconstructing the stigma against sexual relationships between (consenting, informed, adult) close relatives? — as we should those against STIs, genetic abnormalities, and neurological disorders.

      While stigma should not inform any of our choices, risk factors should, and two adults considering having a child owe it to their child to take these into account. The problem here is that people can generally get reliable information about such factors from their doctors, though when it comes to consanguineousness (consanguineity?) the stigma seems to bias even some physicians’ reactions and advice. (Sorry, read recently but can’t find source.)

      Moreover, people aren’t typically asked about their genetic abnormalities by family and friends inquiring about their love life, but “How did you meet?” is common enough, and we should be able to give straightforward and honest answers without fear of reprisal.

  4. This is a really interesting one to me, because the concept fills me with absolute revulsion and disgust (particularly in that I may have experienced a bit of incestuous abuse myself).

    But when I actually THINK about it, I realize that it does fall perfectly and well within the boundaries of what I consider ethical sexual intimacy… that is, adults capable of granting full informed consent, and not harming anyone else (except perhaps any children they conceive… I’d argue that in the case of VERY close relatives, like siblings, they should not have children).

    So it’s sort of an interesting example of how some of us who work hard to be as accepting of sexual/gender variance as possible can still run up against some very powerful, negative emotional responses to things we consider taboo.

    But it’s also an interesting example of how thinking these things through can help overcome such taboos and negative emotional responses.

    • At some point you just have to say, “You know what, I think poop is icky, too, but I don’t want to send coprophiles to jail.”

      And it is deeply amusing to me that the vast, vast majority of our problems could be solved through the radical step of requiring and recognizing consent.

  5. Up to this point I was of the opinion that relationships between close relatives is ok (adult, consent, so on), but I had a problem with them having children. It would be terribly unfair against the offspring, no? But then I thought about my views on abortion. I have no problem denying that the ‘potential’ living inside a woman has a right to live. It the woman’s choice and so on. But here I am worrying about its well-being. No. I’m worrying about the well-being of unconceived ‘potential’.

    So it seems to me that in the Venn’s diagram of my opinions there was an area for the idea that every fetus has the right to be healthy when abortioned. Now I don’t know anymore. I have to think about this.

  6. With all due respect, please check your privilege. To some of us in the community, the idea that the genetic makeup of our children would make them somehow less desirable is incredibly disconcerting. Some people have struggled with issues like genetic diseases and passing them on to our offspring, and the suggestion that having children with a particular genetic makeup is “unfair” delegitimizes those families. Additionally, in the US, ideas about protecting the genetic fitness of offspring have a long history of being used to perpetuate eugenics and the forcible sterilization of poor people and racial minorities. See Buck v. Bell, “three generations of imbeciles is enough,” etc. “I [have] a problem with them having children” is an incredibly problematic statement, almost regardless of the context.

    • Then call it problematic in a way that is meant to encourage discourse rather than put other people on the defensive. I’m not trying to tone troll you here, I just think you’re being really harsh to someone who has already admitted their own ignorance and the inadequacy of their preconceptions.

      And I don’t have Huntington’s, but that’s hardly the only thing one might worry about passing on to one’s biological children.

  7. “I have a problem with them having children” and “I think they should be legally prohibited from having children” are very different statements, Jason, and it’s not helpful to pretend otherwise.

    We might draw the line at different places, but you gotta admit that the “I have a problem with them having children” line exists. I don’t think you’re so scared of somehow causing the forcible sterilization of poor people to acknowledge that a couple that knows their status, but that has four, five, six children that all have Taysach’s anyway, that all die horrible deaths as toddlers, is doing something morally reprehensible and unfair to the child.

    • This. While we must all be aware of the eugenics history in this country as a context for these discussions, that doesn’t mean people cannot express concern about certain genetic issues being passed down.

      Hell, I couldn’t donate my eggs because there’s too much cancer on one side of my family. I don’t think the egg donation place was being discriminatory when they said “the amount of cancer would scare away a lot of parents”. It’s true. If there’s a fuckload of cancer in someone’s family medical history, that’s an issue they have to consider when it comes to reproduction.

      • But saying “You have lots of cancer in your family so we can’t take your eggs” is different from “You should never breed, and we are de-legitimizing any children you may choose to have because they’re not genetically good enough.”

  8. I have a totally useless personal experience to add. I have two relatives (they are 1st cousins to each other) who are married and have 3 kids. They should not be married but that’s because they’re both idiots, not because of any arguments against marriage for 1st cousins. Their first two kids have no problems but their third child has a very rare (1/150 million) genetic disease which causes dwarfism and other developmental and brain issues (he’s 12 and he’s already had to have brain surgery to avoid a stroke). The condition was not identified until after he was born (they knew there was a problem close to birth but they thought he was just malnourished, dwarfism was not suspected until about 3 months after his birth and the condition identified in full at about 3 years). They were tested for genetic issues, I don’t know whether they didn’t test for this because it’s rare or they didn’t have a test at that time (they do now).

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