Iceland’s gene pool sure has been under heavy scrutiny this last month. Thanks to a joke taken a little bit too literally by the international media, a whole bunch of people are probably now under the impression that Icelanders are so related that they need an app to prevent incest. Now, we are a pretty homogenous nation, as founder of deCODE Genetics Kári Stefánsson says, but we’re not THAT homogeneous.
DeCODE Genetics “has discovered key risk factors for dozens of common diseases” due in part to Iceland’s small, homogeneous gene pool. So just how homogeneous are we?
We are homogeneous in the sense that all of us are rooted in a relatively few individuals who lived many, many centuries back. This means that two random Icelanders will share more of the genome than two Americans, but they share just tiny little pieces of DNA because the genome has been broken up by recombination over many generations. There is the so-called Founder Effect in our population meaning that a few individuals who lived in the past are responsible for a large percentage of the population. This makes it much easier for us to find rare mutations that cause diseases.
According to a chapter on impediments to marriage in Iceland’s Law in Respect of Marriage No. 31, “Persons related by direct descent may not intermarry, and the same shall apply to siblings.” This, however, means that Icelanders can marry their second cousins. You must have data on this; is this practice prevalent today? Was it in the past?
We published a paper [“An Association Between the Kinship and Fertility of Human Couples,” SCIENCE VOL 319] a few years back which showed that the more closely related parents were, the more children they had, which is sort of counterintuitive. Then when we looked at whether there was a relationship between how closely related the parents were and how many children their children had, it was still the case that the more closely related the parents were, the more children their children had, except when the parents were first cousins. This means, if the first cousins had children, those children were probably handicapped. So that’s an indirect answer to your question.
So it’s okay for second cousins to procreate?
Second cousins will have healthy children, at least that is what our data indicate. So biologically it is fine. Also, keep in mind that our definition of a species is a group of individuals who are closely enough related to each other to be able to have offspring. So implicit in our definition of a species is a relationship between individuals. I’m not at all promoting or recommending that second cousins procreate; I’m just saying that our data do not indicate that there will be biological disasters, though there may be social disasters. It is definitely frowned upon and probably should be.
The law also states that, “Examination of impediments to marriage shall be performed by persons empowered to perform marriage ceremonies…” Do priests actually need to consult Íslendingabók to verify that they are not marrying off persons related by direct descent?
I have no idea what the priests do in general. I do not know whether they consult Íslendingabók. I do not know if they like movies, I don’t know what they like to listen to, I don’t know what they like to eat. I know nothing about priests. I don’t go barhopping with priests. I know nothing.
How does the incest alarm work? How closely related do you have to be to set it off? How as this determined?
You know, the incest alarm on this app was just a joke. On the tenth anniversary of our Íslendingabók database, we launched a competition to create a mobile version of the site, which was won by computer nerds who put together an app that was visually appealing and easy to use. When they got the award, they created this tongue-in-cheek part, but they were just joking. The international press was fooled.