Islam and first cousin marriages

[Rev. Rye]

I was always under the impression from what I had heard that the effect wasn't so large at least for the occasional first cousin marriage. I remain sceptical...

It was my understanding that first cousin coupling doesn't seem, in and of itself, to give too high a risk of increased birth defects [Technically, it does seem to double it, but given that it's a doubling from 2% to 4%, it doesn't seem a terribly large risk].

However, it's very difficult for me to believe that a long-term cycle of cousin coupling won't end in genetic disaster:



This is the pedigree of King Charles II of Spain, the results of over a century of exclusive inbreeding, with most of his ancestors coming back to one woman: Queen Joanna. If that wasn't bad enough, Joanna's nickname was "Joanna the Mad." The last child in his pedigree born with outside DNA, his great-grandomother/great-great-grandmother/likely other relationships Maria Anna of Barvaria was born 110 years before him. Geneticists say his genome was likely more homozygous than the child of two siblings.

You can look for more information on the genetic freakshow that was Carlos Segundo on Wikipedia, but here's the short version: he had an excessively long underbite so long he could barely chew, did not learn to speak until the age of four (and even then could barely be understood due to his oversized tongue) or walk until the age of eight. He wasn't expected to go to school or even keep clean (although half-brother John of Austria eventually convinced him to at least comb his hair). By the end, in the words of a doctor performing his autopsy, his body "did not contain a single drop of blood; his heart was the size of a peppercorn; his lungs corroded; his intestines rotten and gangrenous; he had a single testicle, black as coal, and his head was full of water."

Granted, it's a bit more extreme than the situation with Islamic inbreeding, but it's not hard to see how a long-term cycle of first cousin marriages would lead to bad consequences.

In Gone With the Wind, it's said "The Wilkes and Hamiltons always marry their own cousins." One shudders to see what the Wilkes family would have ended up like after all this time.