Gene Expression

Marriage equality, inbreeding style

The New York Times has an article on cousin marriage that’s up. Here’s some important bits:

Shane Winters, 37, whom she now playfully refers to as her “cusband,” proposed to her at a surprise birthday party in front of family and friends, and the two are now trying to have a baby. They are not concerned about genetic defects, Ms. Spring-Winters said, and their fertility doctor told them he saw no problem with having children.

The couple — she is a second-grade teacher and he builds furniture — held their wedding last summer on a lake near this tiny town in central Pennsylvania. But their official marriage took place a month earlier in Maryland, at Annapolis City Hall, because marriage between first cousins is illegal in Pennsylvania — and in 24 other states, according to the National Conference of State Legislatures — under laws enacted mostly in the 19th century.

For the most part, scientists studying the phenomenon worldwide are finding evidence that the risk of birth defects and mortality is less significant than previously thought. A widely disseminated study published in The Journal of Genetic Counseling in 2002 said that the risk of serious genetic defects like spina bifida and cystic fibrosis in the children of first cousins indeed exists but that it is rather small, 1.7 to 2.8 percentage points higher than for children of unrelated parents, who face a 3 to 4 percent risk — or about the equivalent of that in children of women giving birth in their early 40s. The study also said the risk of mortality for children of first cousins was 4.4 percentage points higher.

More-recent studies suggest that the risks may be even lower. In September, Alan Bittles, a researcher at the Centre for Comparative Genomics at Murdoch University in Australia and one of the authors of the 2002 study, published a paper in Proceedings of the National Academy of Sciences that reported that the mortality rate was closer to 3.5 percentage points higher. He said he expected ongoing research to find the risk of defects to be lower than previously assumed as well.

“It’s never as simple as people make it out to be,” said Dr. Bittles, noting that very early studies did not account for factors like access to prenatal health care, and did not distinguish between couples like Ms. Spring-Winters and her husband, the first cousins in a family to marry, and those who are part of groups in which the practice is common over generations and has led to high rates of genetic disorders. “But the widely accepted scare stories — even within academia — and the belief that cousin marriage is inevitably harmful have declined in the face of some of the data we’ve been producing,” he said.

Diane B. Paul, a professor emerita of political science at the University of Massachusetts, Boston, and a research associate in zoology at Harvard, was an author of a paper published last year in the journal PLoS Biology that described the difficulty of generalizing about the potential for birth defects or increased mortality in the children of cousins. Each couple’s risk depends on the individuals’ particular genetic makeup, she said, which means “it’s very difficult to determine.” And even the small average risk of defects reported in the 2002 study, she added, represents nearly double the risk to children of unrelated parents.

As a religious Methodist, she said, she also worried that marrying her cousin would be wrong in the eyes of her church. But as it turned out, the Methodist Church has no official position on marriage between cousins, unlike the Roman Catholic Church, which requires cousins to obtain dispensation before marrying. And after talking to a relative who is a Baptist minister, Ms. Spring-Winters said, she discovered that the Bible does not say anything explicitly negative about cousin marriage, although it does list examples of sexual impurity, including relations with “close relatives,” like sisters, stepchildren, grandchildren, aunts and stepsisters; and those between mothers and sons, and fathers and daughters.

“If the Bible said no, we wouldn’t have done it,” she said.

A few salient points noted above:

* If you want to minimize the perception of risks of cousin marriage, emphasize the small increment in absolute percent increase in risk. For example, a 3% chance of congenital defect vs. a 1.5% chance.

* If you want to maximize the perception of the risks of cousin marriage, emphasize the change in relative odds. Instead of a 1.5% incremental increase in the risk, you are doubling the risk! Sounds much scarier.

* There is a major distinction between cousin marriages in societies where the practice is rare, and cousin marriages in societies where they are common and customary. In the latter cases the coefficient of relatedness will be far greater than in the former cases. To label them both “cousin marriages” is a function of cultural perception, not genetic reality in terms of equivalence.

* Increased risks may make a younger woman equivalent to a 40 year old in the prenatal precautions needed. That is an informative way to present the health and medical consequences, as naturally the costs will be greater.

* We do not ban women of the age of 40 from reproducing. Nor do we ban those with genetic diseases from reproducing (well, we all have genetic diseases, so perhaps genetic diseases which are judged to be chronic). The ban on cousin marriage is a function of culture.

* The individual above is not a close reader of the Bible, cousin marriage was practiced by the Hebrews. Rebecca, the wife of Isaac, was a cousin (Abraham was Rebecca’s great-uncle). Their son, Jacob, married his cousin, Rachael, the niece of Rebecca. Cousin marriage declined in Medieval Europe through bans introduced by the Roman Catholic Church (bans imposed selectively and often opportunistically, since the official degree of relationship banned was so extreme that violation was the norm). The Reformation brought about a collapse of such bans on cousin marriage, ergo, the marriage of Charles Darwin to his cousin Emma Wedgewood. Cousin marriage declined in Europe again with the rise of modern transportation, greater mobility and concomitant expansion of the mate market, and finally the decline of the landed aristocracy which was invested in preserving old wealth rather than producing new wealth (marrying a cousin often kept property “in the family”).

* The ban on cousin marriage did have a eugenical aspect to it. Charles Darwin himself was worried about ailments his children suffered which might have been an outcome of his marriage to Emma, as it was consanguineous. There are many classes of illnesses, generally recessive diseases, where the increased risk from cousin marriages is marginal, but most who suffer are the products of cousin marriages. In the age of national healthcare where the decisions of our fellow citizens hit us in the pocketbooks, rather than focus on cousin marriages I think it might behoove us to revisit the constraints that society as a collective may place on the choices of individuals more generally.

Happy Thanksgiving!

Comments

  1. #1 anisogamy
    November 26, 2009

    I may have to use this in my class next semester. Thanks!

  2. #2 Duae Quartunciae
    November 26, 2009

    My brother and his first cousin married, and recently celebrated their 25th anniversary. The father of the bride and of the groom were full brothers. There’s no prior history of intermarriage in the family, so any increased risk was small; but they did take advice on the matter before starting a family. They now have two daughters, who are smart, well adjusted, happy and healthy. I may be biased, but this family represents one of the strongest and most positive family units I have ever seen. It all came as a bit of a surprise to the rest of the extended family at the time; but we are now well used to it and approve without reservation. There’s no legal impediment in our jurisdiction — Australia. It’s also highly unusual and many people are taken aback on discovering the relationship; but only very few people really react negatively. Its their loss.

  3. #3 toto
    November 26, 2009

    The difference in perception is fascinating. In the West, it’s like – “Eww!”. In the “Muslim world”, it’s seen as not only acceptable, but actually desirable. As you point out, religious scriptures do not explain this difference – so I wonder where it comes from.

    Wiki says cousin marriage is also seen favourably in South India – but not in North India. You would expect to see North Indians more influenced by their Islamic neighbours and (in some cases) actual co-ethnics (Pubjabis). Or is it actually one way for North Indians to distantiate themselves from the Muslim “invaders”?

  4. #4 razib
    November 26, 2009

    toto, in many parts of north india there is an obligate requirement for village-village exogamy and not intermarriage between ‘gotras.’ don’t know if this predates or postdates islam. south india had its own practices before the arrival of hinduism. in fact, they practice uncle-niece marriage (excepting kerala).

  5. #5 Tod
    November 26, 2009

    It doesn’t seem to have done the Ashkenazim any harm, or at least the gain was more than the loss.

  6. #6 megan
    November 26, 2009

    To get to the numbers of humanity there are now, cousin marriages, especially first cousin marriages HAD to have been common. But with nomadic migrations and invasions including with cultural policies the idea that better ‘stock’ and breeding hardiness could come from a wider influx of genes started to be the norm. I’d say advancement in plant/animal breed helped undercut the commonality in societies plus as the general human population and ease of travel increased the pressure to marry within a region or village decreased.

    If the use of Islam is being made as an example, I would posit it has more to do with the initial Arabic cultural norms that also use inter-familial ARRANGED marriages as a means of female fecundity and genetic offspring control.

    My cousins and relatives perceive treat each other/behave as siblings-immediate relatives, especially as we grew up together. Marriage, dating or sex was for outside of the direct family lines, if by accident maybe 3rd or 4th cousin, best by marriage.

  7. #7 Richard Harper
    November 26, 2009

    Wishing I had a specific cite, but anyway–

    Cousin marriage sometimes gets discussed in the context of attempts to explain the Flynn effect of intelligence test scores improving over the decades as a possible effect of heterosis.

    So for example from page 69 of the 85 page pdf of the abstracts from the ISIR 2008 conference: “In particular, the relatively small effect of inbreeding on IQ (3 points in the offspring of first cousins)..”
    http://www.isironline.org/meeting/pdfs/program2008.pdf

    See also:
    Mingroni, M. A. (2007). Resolving the IQ paradox: heterosis as a cause of the Flynn effect
    and other trends. Psychological Review, 114(3), 806-829.

  8. #8 dave
    November 27, 2009

    I come from a large American Irish Catholic family, but my own family moved around and I only visited for holidays. Although nothing happened, that I’m aware, there seemed a large amount of sexual tension between my cousins and me and my brothers. And there were two of my cousins, one a first cousin, who I admit I felt a strong attraction, but made sure I never acted on because I thought it was wrong.

    Among my cousins (literally hundreds) the relationship seemed more like brother-sister since they all spent so much time around each other. My one cousin grew up to be almost everything I’m looking for in a wife. And she married a man remarkably similar to me. It never occurred to me to pursue her, though. My reaction was more like, oh, this is an unfortunate feeling that I need to suppress.

  9. #9 Donna B.
    November 27, 2009

    #8, dave — I can relate (pun intended!)

    However, I was never quite sure who was my first cousin, first step-cousin, half first cousin… or whatever variation you might come up with.

    And then there were the pseudo-aunts and uncles… those I knew I was not actually related to, but they felt so close. I was reluctant to consider those “cousins” as mates.

    Though both sides of my family would be considered redneck hillbilly hicks (three different things, but often conflated), in researching my family history, I’ve not found one case of any cousin unions.

    In fact, the closest I’ve found is that my youngest daughter and her husband share an ancestor back in the 1700s.

    However, my husband’s family history contains three instances of first cousins marrying.

    Could it be a cultural thing? In my husband’s genealogy, it is the Huguenot element in S. Carolina with the first cousin marriages.

    My mother’s family (quite well-documented) had no first cousin marriages, though there were multiple instances of siblings from one family marrying siblings from another.

    Her heritage is a mix of Scots-Irish and English.

    I find similar in my father’s family which is English, Irish, Dutch, and Native American.

  10. #10 Charles Iliya Krempeaux
    November 27, 2009

    Doesn’t 1st cousin breeding also have a “cleansing” effect? Removing harmful alleles?

    In the age of national healthcare where the decisions of our fellow citizens hit us in the pocketbooks, rather than focus on cousin marriages I think it might behoove us to revisit the constraints that society as a collective may place on the choices of individuals more generally.

    That’s one of the things that some of the people advocating against Nationalized Healthcare warned would happen. I.e., it would be used as a reason/excuse to take away individual liberty.

  11. #11 Adela
    November 27, 2009

    There were and still are class issues in cousin marriage as it is one of the ways family dynasties maintain wealth and keep it in the family lineage, hence inbred royalty.

  12. #12 Richard Harper
    November 27, 2009

    For anyone interested in the psychology of incest avoidance in humans, professor Debra Lieberman has published several excellent papers on this subject, as well as the broader topic of kin-recognition psychology in humans. As an oversimplification, many modern societies (and Victorian Era etcetera) raise children in social structures where kin-recognition among children fails to develop, thus leading to an absence of incest-avoidance. (… Using the term incest here in a technical not moral sense of course.)
    http://www.debralieberman.com/html/cv.html

  13. #13 Bob
    November 27, 2009

    For relatively common recessive disorders, the risk in the offspring of first cousin matings is only slightly increased compared to the general population risk but for rare recessive disorders, the risk is dramatically higher for offspring of cousin parents.

  14. #14 rec1man
    November 27, 2009

    I saw a study done on North Indian muslims, and they found that first cousin marriage drops IQ by 8 ( 0.5 SD )

  15. #15 Eric Johnson
    November 28, 2009

    Better to keep our taboos and our laws. Not so much because of occasional one-shot inbreeding; rather because of the possibility of widespread inbreeding, or less-widespread but multi-generational inbreeding.

The site is currently under maintenance and will be back shortly. New comments have been disabled during this time, please check back soon.