The Drive-By Truckers – “The Deeper In”

Geneticists love nothing more than a good inbred organism with which to work – yep, we’re fun people. When you’re trying to determine the genetic source of a particular trait, the less genetic variability the better. With a nicely inbred genetic model organism, the researcher can assume that when a interesting heritable trait is found that everything else is the same except for the mutation that causes that trait. So, the laboratory strains of model genetic organisms that most researchers work with tend to be highly inbred.

That’s fine for your average laboratory fruit fly, but inbreeding tends not to work so well in the wild – just take a look at the guests on the Jerry Springer Show or your average pug. The biggest problem that you run across if you have a lot of relations with the relations is that you increase the likelihood of accumulating harmful mutations. For example, if a recessive mutation that is responsible for some horrible disease is lurking around in a family’s genome, children are more likely to end up with two copies of the mutation – and thus the disease – if their parents both come from the same family.

This week a group of researchers from Iceland published results in Science (DOI: 10.1126/science.1150232) suggesting that a little bit of inbreeding isn’t always a bad
thing. There have been studies in the past that provided evidence that consanguineous unions (relations between relations) provided economic advantages in some cultures by keeping land and resources within an extended family. Biologically, previous demographic studies have reported that when parents were related – usually first or second cousins – they tended to produce more offspring. [Insert your own Appalachia joke here.] But while this correlation is fairly robust, it has never been clear how much of this was due to differences in socio-economic factors between cultures in which consanguineous relations were common versus those in which they were not. In a way, it’s a classic example of a nature versus nurture debate – how much of this increased fertility is due to biology and how much due to cultural variables.

The Icelandic team, led by Agnar Helgason of deCODE Genetics and the University of Iceland, plowed through a century and a half of genealogical records tracing the ancestry of over 160,000 of their countrymen in an attempt to address this question. What makes this population useful for the question at hand is that it is smaller and more socioeconomically homogenous than populations used in previous studies. Helgason’s team assumes that this allows them to ignore the cultural variables and just focus on biological issues. Helgason and his colleagues found, as had previous studies, that the more closely related couples tended to have more children and grandchildren. The catch is that the children of the most closely related parents – first or second cousins – died younger and reproduced less. Interestingly, even though the instances of consanguineous relationships have declined steadily since 1800 (from 0.5% in 1800 to 0.05% in 1950), the relationship between kinship and increased fertility is maintained.

The conclusion that the Icelandic team draws is that because they have effectively eliminated the socioeconomic factors in their “culturally homogenous” population that their is a biological advantage in terms of reproductive success to limited inbreeding. The problem is that the reader is asked to take the researchers’ word for this claim on spec. The authors cite a UN Human Development Report and unpublished report from York University in support but neither of these reports have undergone the rigorous peer review process to which most legitimate scientific research is subjected. This isn’t to say that their results are bogus, it is probably a pretty safe assumption that prior to the 1950’s Iceland was a very socially (and genetically) homogenous culture. The fact that the general trends regarding reproductive success are maintained over a period of 150 years is a pretty strong indication that it occurs independently of changes in cultural mores. If their results are repeatable and robust they suggest that limited inbreeding does improve reproductive success – potentially a useful innovation for small geographically isolated populations.

I guess the take home message is if you have a hankering for your cousin it isn’t going to be Biology that tells you to cool down.

Image Credits:

The wonderful photo of Icelandic faces at the start of this post is from Stuck in Customs.

Dancing Icelanders

Hot springs

The Drive By Truckers’ wonderful “Decoration Day” is available from , Amazon and eMusic.