Inbreeding: Downfall of a Dynasty

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The powerful Habsburg dynasty that ruled Spain for nearly 200 years came to an abrupt end in 1700 with the death of King Charles II, who left no heirs to the throne.

The termination of that royal lineage may be the result of frequent inbreeding of the line, which may have left Charles II ill and infertile, a new study suggests.

The House of Habsburg was one of the major royal houses of Europe for many centuries. The Habsburgs ruled over Austria for more than six centuries, eventually coming to rule (through marriages) over Bohemia, Hungary and Spain.

But, historical data show that "in order to keep their heritage in their own hands, the Spanish Habsburgs began to intermarry more and more frequently among themselves," the authors of the new study wrote.

Records show that the Spanish Habsburg kings frequently engaged in consanguineous marriage (or marriage between biological relatives); nine of the 11 marriages that occurred over the dynasty's 200-year reign were consanguineous, with two uncle-niece marriages and one first-cousin marriage.

Gonzalo Alvarez and his colleagues at the University of Santiago de Compostela in Spain calculated what is called the inbreeding coefficient for each individual across 16 generations of the Habsburgs, using genealogical information for Charles II and 3,000 of his relatives and ancestors. The inbreeding coefficient indicates the likelihood that an individual would receive two identical genes at a given position on a chromosome because of the relatedness of their parents.

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