While researching a different topic I stumbled upon the following 2006 report on the Internet. It contains comprehensive estimates for the prevalence of birth defects all around the world. The relevant graph is reprinted below (you can click on it to get a bigger picture).
What leaps out at first sight is the sheer extent to which the worst affected countries are Muslim ones. Of the 29 countries with a birth defects prevalence of over 70/1,000 births, only 5 are not majority Muslim. 9 of the worst 10 are Muslim. Furthermore, whereas those five are all very poor African nations, the Muslim ones include very rich Arab states like the UAE, Kuwait, and Bahrain.
What explains this? Is it something in the water?
Almost certainly this is due to high rates of consanguineous marriages. As hbd* chick has frequently pointed out, the institution of father’s brother’s daughter is prevalent and commonly accepted pretty much only within the historic borders of the 8th century Caliphate. This is arguably a very regressive custom: While it promotes familial loyalty, the side cost is high rates of clannishness, nepotism, depressed national IQ’s… and, as graphically illustrated above, birth defects.
The country with the least amount of birth defects per newborn is estimated to be France.