Editor’s note: (June 4, 2024) This post has been changed since it was first published.
The Royal House of Habsburg, one of the most powerful dynasties of Medieval and Renaissance Europe, reigned over much of Europe for centuries. But genetic inheritance and the perils of inbreeding may explain their demise.
Like many royal families, their expansion and hold on power came about in part through inter-family marriages. But over time, generation after generation of inbreeding helped contribute to some of the physical ailments that often plagued the family and the distinctive look with their big lower lips, long noses, and the unique “Habsburg jaw.” Research published in the Annals of Human Biology describes how this inbreeding likely doomed the dynasty.
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Understanding Consanguinity: Inbreeding’s Role in Genetic Disorders
Inbreeding is when two closely related individuals, who inherited some identical segments of DNA from the same ancestor(s), have children. The term genetic counselors typically use for inbreeding is “consanguinity,” which means “of the same blood” and is pronounced, “con-san-gwinity.”
The degree of relationship between the two individuals matters a lot. Children of parents who are brother and sister are more consanguineous (“con-sang-win-us”) than the children of two people who are first cousins. For similar reasons, consanguinity within the same family over multiple generations increases the risk for hereditary disorders in more than one isolated instance of a consanguineous union in a family tree.
Beginning in the early 12th century, they quickly expanded their realm. They did this through a series of strategically executed marriages, from the mountains of Switzerland to a territory that included swaths of Austria, Hungary, Italy, France, and Spain. The Spanish branch of the Habsburg dynasty helped create an empire that reached its apex in the 16th and 17th centuries. They controlled land from the Philippines to the Americas.
Yet the Habsburgs are known not only for controlling vast tracts of Europe but also for maintaining control by rarely marrying outside the dynasty.
Habsburg Inbreeding
By the end of the 17th century, the results of their marital practices had become apparent. Family members had distinctive protruding lips, a high rate of infant mortality and a host of other health problems.
Could the same marital practices that helped bring the Habsburg dynasty to power also have led to its demise?
In PLoS One, scientists from Spain’s University of Santiago de Compostela argue it did. They said that inbreeding so incapacitated the Habsburgs that by the death of King Charles II of Spain in 1700, they were virtually unable to reproduce.
From 1516 to 1700, it has been estimated that over 80% of marriages within the Spanish branch of the Habsburg dynasty were consanguineous. In other words, they were marriages between close blood relatives. These unions often took the form of marriages between first cousins, double-first cousins, and uncles/nieces. Infant and child mortality rose to 50% among Spanish Habsburgs, much higher than the average for the period.
The Tragic Reign of Charles II: A Victim of Inbreeding?
However, the final Habsburg king of Spain, Charles II, was perhaps the most unfortunate result of these unions. Also known as “El Hechizado” (“The Hexed”), Charles was severely deformed. The so-called “Habsburg Lip”, a form of mandibular prognathism often seen among members of the Habsburg Dynasty, was so pronounced in Charles’ case. So much so that it was difficult for him to speak. An enlarged tongue, gastrointestinal problems, mental retardation, and possible growth problems meant that Charles was raised almost as an infant until the age of 10. Even as he grew older, he was never able to govern effectively. His rule saw the rapid decline of the Empire, only exacerbated by his death in 1700.
However, there has been little scientific research for all the speculation and anecdotal evidence of the negative impact of inbreeding on the House of Habsburg. So, there is no hard evidence of whether inbreeding actually played a role in the demise of the Hapsburg line. The authors of this study sought to achieve this goal by examining genealogical information. To do that, they looked at family pedigrees for the eight royal families connected with the Habsburg dynasty.
Quantifying Royal Inbreeding: The Habsburg Family Tree Analysis
They analyzed the family pedigrees of over 3,000 individuals spanning 16 generations. They then used this information to calculate the inbreeding coefficient for each family member. The inbreeding coefficient is simply a measure of the chance that someone will receive identical genes from both parents.
Unsurprisingly, the authors found elevated inbreeding coefficients for many Habsburgs. In fact, the levels increase consistently from the earliest Spanish Habsburgs. This goes from King Philip I (1478-1506) to the last Spanish Habsburg king Charles II. Some of the Habsburgs – notably Charles II – had an inbreeding coefficient nearly twice what one would expect, given the level of relatedness between his mother and father. In other words, although Charles’ parents were related to each other as uncle and niece, his inbreeding coefficient fell at the same level as someone whose parents were brother and sister.
These unexpectedly high levels indicate consanguineous marriages, like that of Charles’ parents. These unions had been happening along the Habsburg line for hundreds of years. This practice came to a head with the birth of Charles, whose inbreeding coefficient was the highest of all the Spanish Habsburgs. His physical deformities were also the most severe.
Further, the authors argue that Charles’ ill health directly resulted from centuries of consanguineous unions. Expressly, they point to a growth hormone deficiency and severe renal tubular acidosis. These may have accounted for his short stature and many physical deformities and ailments. These diseases are pretty rare in the general population. But the fact that so many of Charles’ ancestors were related to each other would have increased his chances of inheriting the genes associated with them. Whether Charles suffered from these specific diseases is still open to interpretation. However, his physical and mental difficulties prevented him from fathering any heirs to the throne.
The Habsburg dynasty in Spain ended when Charles passed away in 1700, a few days shy of his 39th birthday.
Genetics and Personalized Health in the 21st Century
The Habsburg dynasty’s story highlights genetics’ profound impact on health and well-being, a reality that resonates even more strongly in the 21st century. Today, advancements in genetic research have opened up a new frontier in personalized healthcare.
Understanding one’s genetic makeup can provide insights into potential health risks, carrier status for certain conditions, and how individuals might respond to different medications. This knowledge empowers individuals to make informed decisions about their health, from lifestyle choices to proactive screenings and treatments.
23andMe, at the forefront of personal genetics, provides individuals with access to this valuable information. While rooted in the past, the Habsburg narrative serves as a compelling reminder of the power of genetics in shaping health outcomes.
Find out if your genetics might Increase your risk for any health conditions with 23andMe.