Innocent Sibling Incest: Is It Really So Bad?

Did you see the story making the rounds yesterday (mentioned briefly on MarieClaire.com) about a young man and woman in Ireland who had a baby together before finding out they were half-siblings?

Long story short (for the long story, check out London's Daily Mail), the related couple have decided to stay together. They love each other, they have a kid.

The couple's mutual father is having a hard time with the whole thing, and plenty of other people think it's gross, too.

My reaction: What's the big deal?

As Yale psychologist Paul Bloom writes in his new book How Pleasure Works: The New Science of Why We Like What We Like, the "evolutionary rationale for incest avoidance is that it is a bad idea, genetically, to have children with your kin, because they share too many of your genes." In other words, we've developed a sense of disgust about sibling incest because it could lead to deformed babies.

But in this case, the couple already had a baby before finding out they were related. (They say they're going to have more kids together, too, although I hope they're going to get testing done to make sure the kids won't be born unhealthy.)

What's more, Bloom indicates that we don't seem to be born with some kind of built-in detection device that tells us who our siblings are — if we were raised separately, with no knowledge of our kinship, we'd never be able to figure it out on our own. But simply being raised with someone — even if you aren't biologically related to him or her — is enough to make any sexual attraction between you very unlikely. For instance, studies done on arranged marriages in China and Taiwan where families adopt a female baby so they can marry her off to their sons one day have found that sexual relationships are unlikely to occur. In fact, a study done in 2007 found that the longer you live with a sibling (or an adopted sibling or someone sibling-like), the more sexual aversion you will have to him or her. The biggest libido killer of all, sibling-wise, is to see a younger sibling getting cared for by the mother you share.

Now, in case it needs to be said, I understand that incest involving a parent or even a parental figure is an evil, evil thing. (I still feel for poor Mackenzie Phillips and think her father was one seriously screwed-up, disgusting, sad man.) The idea of two siblings or half-siblings who grew up together having sex makes me shudder. I understand that almost always incest is disgusting and that it can be very psychologically harmful for a person who has been coerced or manipulated into it.

But in the case of these two people, I really don't think it's a big deal. They're basically strangers. They came out of different mothers. They happen to share some genetic material. So what? I don't think it's morally wrong for them to be together. In fact, considering they have a kid together — and they love each other — I'd say that the morally right thing is staying together.

Now that I've laid this entire argument out, I guess what I'm doing here is asking us to think about our socialized knee-jerk reactions to things. Sure, it's important to have a strong social taboo against incest. All the same, we're smart people. Shouldn't we be able to see that a case like this is different?

What do you think?