High class cousin marriage

A reader writes:

Cousin marriages were extremely common among European aristocrats and royals. After the House of Hapsburg split into the Spanish and the Austrian branch, it was customary that a scion of the Spanish Hapsburgs would marry a cousin from the Austrian branch. Charles II, the last Hapsburg king of Spain and whose death in 1700 led to the War of Spanish Succesion, had only 6 great-great-grandparents. Not surprisingly, he was not the fittest and healthiest person that ever lived.

The poor king was so inbred that he was mentally retarded, had the protruding lower "Hapsburg Jaw" so badly he couldn't chew, and was sterile and/or impotent. His death without issue led to the huge war between England and France in which John Churchill, the Duke of Marlborough, won the famous victory of Blenheim in 1704. For more on the Hapsburgs, see this late 1999 essay awarding them the title of "Best Hideously Inbred Royal Family of the Millennium."

My published articles are archived at iSteve.com -- Steve Sailer