Inbreeding

A study of the extended family tree of the House of Hapsburg has found that the last Spanish Hapsburg king, Charles II, was the offspring of a marriage that was almost as genetically inbred as an incestuous relationship between a brother and sister or parent and child.

Scientists have found that the Hapsburg fashion of marrying their relatives to keep their dynastic heritage intact had dire consequences for subsequent generations, which culminated in the last heir to the Spanish throne being sickly and impotent.

Charles II of Spain was nicknamed El Hechizado – The Hexed – because people at the time thought that his physical and mental disabilities were the result of sorcery. Now a study into the genetics of his immediate ancestors has found that he was so inbred that he probably suffered from at least two inherited disorders.

Despite his deformities and severe health problems, Charles had married twice in the hope of continuing the rule of the Hapsburgs, but he was incapable of fathering an heir and died childless at the age of 39. He was the last of a long line of Hapsburgs and it spelled the end for the Spanish branch of the dynasty.

Scientists believe they can show just how inbred Charles was following a study of more than 3,000 relatives of the Hapsburg family extending over 16 generations. The researchers found that his "inbreeding coefficient" – a measure of the proportion of inbred genes he had inherited from his parents – was on a par with that of the offspring of an incestuous marriage.

Revealed: the interbreeding that ruined the Hapsburgs