DISCOVER MAGAZINE - INDIVIDUAL - SOCIAL RISKS OF COUSIN MARRIAGE by Razib Khan
A very interesting article from 2010...
EXCERPT
What are the risks of cousin marriage? Most obviously there are recessive diseases. Those illnesses which are expressed when you carry two malfunctional copies of a gene. Cystic fibrosis, tay sachs, various forms of deafness. Why is it that cousins have a higher risk of this occurring? Because two cousins are much more likely than two random individuals to share the same distinct gene from a common ancestor, because their common ancestors are so much more recent. More precisely the coefficient of kinship between two first cousins is 1/8. That means that at any given locus there’s a 1 out of 8 chance that the two individuals will have alleles which are identical by descent, which means that the genetic variant comes down from the same person in the family line.
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Found this one while looking into reasons why the Catholic Church might want to give "special dispensation" in Europe in the 1800's. Don't know if I got that answer, but I have met people born in the United States whose parents were cousins married in the Old Country pre immigration.
