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Iceland’s Genetic Secrets

Inbreeding is supposed to be a bad thing. That’s why researchers were startled to discover the extent of inbreeding evident among residents of the orderly and not-exactly-lascivious Island nation of Iceland.

According to longevity specialist Dr. Nir Barzilai, iceland is one of the most genetically homogeneous countries in the world, “There are a half million Icelandic people in Iceland and they are all offspring of 5 Vikings and 4 Irish women or something like that, so all half a million of them are coming from the same fathers and mothers.”

With the world’s longest male lifespan (79.4 years beating second-ranked Japan’s 79.0), and 11th longest female lifespan, Iceland is clearly doing something right.

Further research showed an even bigger surprise: Inbreeding may have a survival advantage. Marriages between third and fourth cousins in the early 19th and 20th centuries (when adequate records were first kept) actually produced more children and grandchildren than marriages between totally unrelated men and women.

For women born between 1800 and 1824, marriages between third cousins produced an average of 4.04 children and 9.17 grandchildren, while marriages between eighth cousins or more distantly related couples had averages of only 3.34 children and 7.31 grandchildren.

“These are counterintuitive, almost dislikable results,” said Dr. Kari Stefansson, senior author of the paper on the study, published in Feb 2008 in the journal Science.

Dislikable and counterintitive because standard genetics teaches us that children of related couples should have a higher risk of genetic disease. Researchers believe the trend toward a more prodigious relationship with a not-so-distant relative must have some kind of biological basis, though they confess cluelessness as to what biological mechanism could possibly be behind this.

In my mind, the crux of the matter is this: Does this survival advantage stem directly from the genetic consequences of inbreeding, or could marrying your 4th cousin be genetically advantageous for an entirely different reason?

I believe the answers lie in epigenetics, which tells us that genetic changes are not random.

Most longevity scientists still assume survival has to do with avoidance of diseased genes. Epigenetics tells us that survival depends more on the interaction between genes and the environment. This new information turns the whole equation around.

It also helps to explain why inbreeding is so common not just in Iceland, but among primary human cultures as well as animal societies.

The explanation for the increased survival among more closely related individuals may be cultural. Those families who are close-knit enough for third and fourth degree cousins to meet and marry are probably also families that pay more attention to tradition, and that includes traditional foods.

Traditional foods provide our DNA with the information it expects. And only when your DNA gets what it wants can you expect to be all you can be.

Wind-dried fish is a typical, traditional Icelandic staple

Typical and traditional Icelandic foods include:

  • Skyr (cultured milk, similar to yoghurt)
  • Hangikjöt (smoked lamb or mutton)
  • Buttered rúgbrauð (a dark, dense rye bread)
  • Lifrarpylsa (liver sausage)
  • Þorramatur (a buffet of sliced and whole cured meats)

Notice the lack of vegetables, not terrifically surprising for a nation with a growing season averaging 40 days.

Dr. Cate

With over two decades of clinical experience and expertise in genetic and biochemical research, Dr. Cate can help you to reverse metabolic disease and reshape your body.

This Post Has 14 Comments

  1. Cold climate is really, really good for genetics – weeds out the lazy, stupid, non-cooperative, and shortsighted.
    Just imagine what they would be without the narrow family tree and crappy diet!

  2. Hi, Dr. Cate. In one of his lectures on Youtube professor Robert Sapolsky from Stanford indicates that marriages to their third and fourth cousin are prevalent in nature, in hunter – gatherers and have their biological advantages.

    I am not sure which lecture it was, but, according to all the biological research, we as people were designed to marry our 3rd or 4th cousin.

  3. Dr Cate! I love your work, it has answered so many mysteries for me, mashallah. I just had to comment on this and share my experience with this topic. My husband comes from a Palestinian family where inbreeding is quite common, in fact 5 out of his 7 married brothers/sisters are married to first cousins. Similar trends extend throughout his uncles’ and aunts’ families, who also had large families and inter-marrying (8-12 children in most cases). This is not just his family, but typical of much of Palestinian society, particularly in Gaza. However, I always wondered how, if marrying cousins is such a big deal, I never saw any higher rates of birth defects or other signs of genetic disorders than anywhere else in the world. I’m not an expert in genetics, but I thought it might be because of the large number of children, which would expand the gene pool. What do you think of this possibility? On the other hand, eating traditional diets, as you mentioned, is also a compelling answer.
    Now, in our generation, birth rates are starting to go down (4 is about average), but cousin marriages seem to be about the same and people are eating much less healthy diets than they did a generation ago- I guess we’ll have to wait and see what happens with the next generation!

  4. This is really interesting for me to see because I’m Icelandic. In fact we are only about 319.000 inhabitants in Iceland and about 2.000 are foreign.
    I have heard similar stories about our native horse that came with the vikings and has been here with us all this time without any horses coming into he country (forbidden by law), natural selection and inbreeding (in nature) has made it really sturdy and strong breed even though its as big as a pony then its often stronger than the average riding horse. But Icelandic people live long and most of us are very healthy.
    If inbreeding has anything to do with our health and lifespan then i have nothing against inbreeding as long it is not siblings or related in second generation.

  5. I wonder if the greater fecundity of cousins marrying, in addition to being perhaps attributed to more traditional foods, may also imply closer proximity to families. My husband and I are a biracial couple and live nowhere near our families. Raising a large brood without help from extended family would be very taxing on energy and resources of the couple.

    P.S. I loved Deep Nutrition and have been using it and WAPF principles to help my daughter heal from crippling rheumatoid arthritis. After a year, she is back at school full-time with no meds. Thanks for your dedication.

    1. Charlene
      Good point. Of course it depends on the family because I’ve known grandparents who feel obligated to provide candy, soda, and cookies to their grandkids every visit.

  6. Dear Cate, I greatly enjoyed your books and am a big fan! I am about to finish my BSc in Human Nutrition in London in a couple of months. However, I am Icelandic and id like to correct Dr. Nir Barzilai. The population of Iceland was 318,452 on the 1st January 2011 ( we have never reached half a million:)

  7. My question is could it not be that there was not enough spacing of the children that it actually was a health issue taken down into the younger siblings which caused a more distorted look…. Did the pqarents wait until the mothers health had been restored before havign more?

    4th of six and definatley the best looking lol

    1. Annie
      You are correct: Maternal nutrition is key, and a certain amount of time between babies is required to accomplish that. …And I’m glad to hear that things worked out so well for you! :–)

  8. Hi Rosemary. Thank you for reading and commenting. I am not an expert on Irish cuisine, but you’ve got a good list started here and there is a growing heritage movement blossoming in the Southern end of the country. You can even do culinary vacations to learn how to make cheese and sausage. Someday maybe….

    Regarding the sibling study, we did not go into details of the Second Sibling Syndrome research protocol in the book, but it was designed with the kind assistance of Debra Leiberman at the University of Hawaii and several of her graduate students. It involved a photographic survey of over 300 hundred sibling sets standardized against a mathematic model (Marquart’s) with varying facial angles compared subjectively by visual inspection. The team identified a clear and consistent pattern of flattened cheekbones, narrowed jaws and so on as reported in the chapter. Collectively, we logged nearly a thousand hours of time on the study.

  9. Hi Dr Cate: I have two questions/comments. (1) What would you say were the traditional foods of Ireland? Here is a list off Wikipedia:

    Examples of Irish cuisine are Irish stew, and bacon and cabbage (boiled together in water). Boxty, a type of potato pancake, is another traditional dish. A dish mostly particular to Dublin is coddle, which involves boiled pork sausages. Ireland is famous for the Irish breakfast,[3][4] a fried (or grilled) meal generally comprising bacon, egg, sausage, black and white pudding, fried tomato and which may also include fried potato farls or fried potato slices.

    Colcannon is a dish made traditionally of potato and curly kale, or sometimes cabbage. Champ consists of mashed potato into which chopped scallions (spring onions) are mixed.

    While seafood has always been consumed by Irish people …. especially due to the high quality of shellfish available from Ireland’s coastline, e.g. Dublin Bay Prawns, Oysters (many oyster festivals are held annually around the coast where oysters are often served with Guinness, the most notable being held in Galway every September ) as well as other crustaceans. A good example of an Irish dish for shellfish is Dublin Lawyer – Lobster cooked in whiskey and cream. Salmon and cod are perhaps the two most common types of fish used.

    General list: Bacon and cabbage, Barmbrack, Boxty. Carrageen moss, Champ, Coddle, Colcannon, Crubeens, Dulse, Drisheen, Goody, Irish breakfast, Irish stew, Skirts and kidneys, Soda bread
    Ulster fry

    How would you modify this list?

    (2) Also, I enjoyed your book “Deep Nutrition” very, very much. That said, I really think your chapter on older children tending have a more symmetrical appearance and being better looking than younger siblings needs more study before being ready for prime time. While an intriguing concept it seemed ancetodal at best; presenting it on such weak data I felt compromised the credibility of the entire book. I say that as a “fan” of your work so please take it as a constructive criticism. Certainly, as the youngest of eight in ten years, I think there is something to be said about mother’s nutritional state having an affect on a child’s long term health. I do wonder how this works with Dan Coyle’s (author of NYT bestseller, Talent Code) theory that younger children tend to be faster than older siblings?

    Keep up your good work,


  10. HI Laura
    I think, in Iceland’s case, the health benefits that people who married their 3rd and 4th cousin’s enjoyed were probably due in large part to the fact that they also [probably] were living more traditional lifestyles and eating better. And this is just conjecture on my part based on the idea that the families I know who gather together often enough for cousins to meet and mary are also into the traditions of their culture, i.e. traditional foods.

  11. In my opinion we must avoid inbreeding is supposed to be a bad thing Because this survival advantage stem directly from the genetic consequences of inbreeding, we could marrying your 4th cousin be genetically advantageous for an entirely different reason.

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