Don't the Muslims also inter marry? Definitely the straight path to obsolesence.
That's what I was thinking, but I didn't want to say it.
Since Muslims cross ethnic backgrounds, I don't see it would be an issue. You are more likely to see problems with small and/or remote villages that "stick to their own kind" where you may see more distant cousin/distant relative marriage.
Some small-island Greeks have issues like this likely also caused by small gene pool.
I read an article in National Geographic a few years ago about Iraq. It said that the amount of inbreeding is pretty high throughout the Muslim world. Between substandard medine and a general lack of cultural empathy, one can only imagine the sad lives of those with congenital problems.
Called inbreeding ... it will lead to genetic defects within a very few generations. An acquaintance of mine, a Mormon from Utah, told me that he brought a women back from Australia who he met while on mission (whom he married). The elders within the Mormon church, although not exactly condoning the practice aren't discouraging it to any extent either ... reason, it brings in fresh genes to the Mormon gene pool.
Th eproblem is not that the Amish are marrying overly close (i.e., first) cousins. It's that EVERYONE in their family trees are related.
So, let's say there's an different abnormal recessive genes you may carry. But only 1 in a thousand people have those abnormal genes. If you marry a random person to whom you are completely unrelated, YOu have only a 1 in 1000 chance of marrying someone with any one of the same abormal genes you have.
But if you marry your sister, she shares 50% of your genes. So you have a 50-50 chance of both of you passing on the same abnormal gene, in which casem your child would have no functional genes, and would then exhibit the abnormality.
If you marry your first cousin, she carries 25% of your genes. Your second cousin carries only 12.5% of your genes. Now that's getting reasonably safe. Your third cousin carries only 6.25% of your genes, and your fourth cousin, only 3.125% of your genes. Normally, that's a reasonably low risk.
But here's the problem with the Founder effect:
Let's say you marry a woman who is your third cousin. From that relationship, you pick up a 6.25% chance of sharing a damaging recessive gene. But she's a third cousin two different ways, so your risk is now 12.5%. And she's a fourth cousin six different ways. That's another 12.5% risk.
And she's your fifth cousin 20 different ways. And with every step removal, she's your cousin in more ways.
Now, I'm simplifying some math here. If you have 10 1-in-10 chances of an event happening, there is not a 100% chance the event happens. Random chances are linked, so it's not 10%+10%+10%..., but rather 1-(.9*.9*.9,....) So the further you go out (i.e., 12th cousin), the numbers quit simply halving themselves, and start becoming more and more less than half. Otherwise it'd be a certainty we'd all have every genetic ailment, since we're all related, and all our relatives are related, etc., etc.
But you see the problem with the founder's effect, no?