The Genetics of Cousin Marriage

It’s conventional wisdom that procreation between first cousins is unhealthy. But what are the actual genetic risks?

James MacDonald describes some of the risks in a new article. He writes:

“In much of the world, consanguineous marriage between cousins is very common. For most Americans, however, marriage between cousins is at best a punchline, at worst a taboo. In many states, it is illegal for first cousins to get married. The objections are ostensibly based on the risk of genetic problems. But is there an actual risk?”

You can find the article in the JSTOR Daily at:



The article is correct for the first time cousins marry. But in populations where cousin marriage has been going on for multiple generations with out new genes being brought in the prevalence is much greater for the incidence of bad recessive and fixed dominate genes (every body has the same hair cowlick for example). Where land inheritance is important and goes to male heirs, cousin marriage always returns the land or inheritance to the family the next generation. Its how you build a Fiefdom, Sheikdom or preserve the Royal Lands and Kingdom. But, look at the mess the Royal Houses of Europe got into!


The problem in my opinion with the way this type of analysis is always presented is that it focuses on deleterious, so undesirable genes. Up until 100 years ago in the US and Canada (even later in some places), when rural communities were often very isolated, the pool of perspective marriage partners in such communities was very limited and it was very common for cousins at some level to marry. For example my maternal grandmother’s parents were second cousins, one set of her grandparents were first cousins, and when you do a deep, thorough family tree for the area my grandmother grew up you discover that most people were related to nearly everyone else at maybe the 4th, 3rd, and often 2nd or even 1st cousin level. There is no question that the analysis you link is scientifically correct. However, first cousin marriages (and to a much lesser extent 2nd cousin marriages) also increase the probability of the passing on of good, special, or desirable genes. A first cousin couple who each have an extraordinary skill, talent or ability (so one that can be assumed to have some genetic basis) are more likely to pass that “good” trait on to their children than if each married someone totally unrelated. Now whether that possibility outweighs the potential negative consequences is a different issue and obviously hard to assess.


    Hmm — Could it be that it’s not such a good idea after all to close our borders to new immigrants from exotic foreign places who are least likely to share our historically predominant European gene pool? Maybe that Green Card Lottery is not such a bad idea after all.

    Liked by 1 person

Yes, that was deliberate. The royal families are all related to each other through multiple marriages between cousins throughout history.


My great-grandparents were first cousins and yes, there were genetic problems–in fact the family is almost non-existent today except for me and my two brothers–all the women died of a genetic disorder and some of the men had it as well.


Look how well it worked for the Habsburgs, and in the Middle East


The book, “Victoria’s Daughters” is excellent on her off spring. Tsar Alexander, Kaiser Wilhelm and King Edward were cousins. The present Queen and her husband Prince Phillip are cousin, 4th I believe.


The best known genetic aspect of Queen Victoria is haemophilia. However, this appears to have nothing whatsoever to do with inter-marriage of relations as the best bet is that the gene first arose as a spontaneous mutation in her. Thereafter, her descendants got it just because they were her descendants, nothing to do with any marriages of distant cousins.


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