The Incest Argument is Back!

Apparently, the German Ethics Council recently argued that laws forbidding incest between brothers and sisters ought to be abolished. Bloggers on the Catholic Right, always alert for signs that gay marriage is leading us down a slippery slope,* have pounced on the story. Damon Linker, who is not a member of the Catholic Right but does like to ask questions that make progressives uncomfortable, is suggesting that this development, well, ought to make progressives uncomfortable.

So I think it’s a good time to drag out this old post to remind everyone that the Catholic Right, and just about every Christian who has ever used “natural law” to argue against gay marriage, ought to find the story from Germany discomfiting, too. Because they can’t answer Linker’s questions, either.

*For the record, Germany does not recognize same-sex marriage.


From 2012:

Dear Catholic Right:

You know how every time you get into an argument about gay marriage, you ask, “Well, if we allow gay marriage, what logical reason do we have to disallow brother-sister marriages?”

You should really stop that.  Here’s why:

If you are an orthodox Catholic, you probably believe in monogenesis—that is, you believe that all of humanity descended from two original humans, Adam and Eve. You also believe that God commanded Adam and Eve (and by extension all of their children) to be fruitful and multiply. Period. These are non-negotiables, as Pope Pius XII pointed out in his 1950 encyclical Humani Generis.

In order to be fruitful and multiply, Adam and Eve’s kids had to have sex with each other. Ergo, you believe God commanded incest. God can’t command something that’s contrary to God’s will, and no commandment from God can ever be unnatural.

So there’s no getting around it: by that logic, brother-sister incest is natural.

Now, I’ve seen some attempts to explain this away.  One suggestion is that Adam and Eve’s kids got a special dispensation to have incest, but as soon as there were enough people to make incest unnecessary, it became unnatural. That doesn’t fly for two reasons. First, natural law doesn’t work that way—the whole point is to figure out what’s timeless and unchanging. Nothing that was natural for Adam (or his kids) can possibly be unnatural for us.

The second is that it doesn’t square with Old Testament history, which is full of incestuous unions, even hundreds of years after they would have been necessary. Abraham’s marriage to Sarah, for example, came ten generations after Noah. By that time, Abraham could have married plenty of unrelated women—we know Hagar was willing to make him a baby—but he chose Sarah, his father’s daughter. And that union was blessed in the sight of the Lord.

Catholics can rightly point out that Church law has since proscribed brother-sister unions, and that such unions are therefore, for Catholics, now a sin.  But Church law holds no weight in our legal system. This, again, is why you use natural law in your arguments against gay marriage.

So why do we ban brother-sister marriages? Most people will tell you it’s because we don’t want brothers and sisters reproducing, since pregnancies that result from those unions have an unusually high incidence of problems. This wouldn’t have been a problem before the Fall, obviously, because that’s when disease and death entered the world.

But as she ages, every woman is at a greater risk for producing a child with birth defects and genetic disorders. And this risk increases every year of her reproductive life. If a woman gets pregnant at 45, the risk for down syndrome is about 40X higher than it was when she was 25. And I don’t see the Catholic Church arguing against marriage for women over 45, or asking those already married to practice celibacy. Nor should they—I’m just pointing out an inconsistency here.

Besides, we have models for allowing marriage among partners we hope won’t reproduce—several states allow first cousins to marry, but only after they’re too old to produce children. Arizona, for example, allows first cousins to marry if a) they’re both over 65, or b) they get a doctor’s note proving that one partner is infertile.

In the twisted thinking of certain natural lawyers, these marriages are okay because they’re “ordered” towards procreation, even though to enter one, one partner has to prove incapable of reproducing.

So let’s say you live in Arizona. A brother and sister (let’s say the sister is infertile) come up to you and ask you why, legally, they shouldn’t be allowed to marry. What are you going to say?


You can’t argue that it’s unnatural.

You can’t argue that it’s to prevent a risk to potential children.

You can’t argue, in our constitutional system, that it goes against Church law.

So you’re stuck, aren’t you?  It’s best not to bring this subject up.  Seriously, stop.

5 thoughts on “The Incest Argument is Back!

  1. Blargh. I respect Kyle Cupp and Damon Linker, and I think they’re just being gadflies on this. You know what, though? It seems to me that incest is a lot more common and accepted in “traditional” societies than in secular, progressive ones that strongly emphasize consent.

  2. It occurred to me on the drive home that the exact same problem exists with regard to that other bugaboo, polygamy. Where exactly do the Scriptures condemn polygamy? Certainly not in the Old Testament–see Abraham, Jacob, David, Solomon, etc. At least for incest you only have to write off Genesis; for polygamy, you have to write off most of the OT.

    • The Old Testament indeed does not prohibit polygamy, but Christ does in the New Testament: “Whoever divorces his wife and marries another commits adultery.” To call the second union adultery implies that the first union is still in effect and that no subsequent union can be entered into while the first is still in effect. Thus, a man is guilty of adultery if he takes a second wife while the first still lives, whether she is currently living with him or not, but if she dies, he is free to take a new wife, provided that he has not bound himself to a vow not to do so (e.g. via Holy Orders).

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