Tag Archives: inbreeding

Scientists confirm “Habsburg jaw” is the result of royal inbreeding

Charles II of Spain, the last ruler in the Habsburg family line. Note the prominent jaw. Credit: Wikimedia Commons.

The Habsburgs were once the most powerful family in the world, ruling over countries such as the Holy Roman Empire, England, France, Germany, Russia, Poland, Hungary, Portugal, Spain, and the Netherlands. Their lineage lasted for 700 years.

In order to secure its influence, the family relied on generations of intermarriage, but this lack of genetic diversity eventually ended up being their downfall. Now, a new study has confirmed that facial deformities in Habsburg bloodline, colloquially known as the “Habsburg jaw”, can be traced to inbreeding.

The most famous example of mandibular prognathism, otherwise known as “Habsburg jaw”, was Charles II of Spain. He was the last king of the Spanish Hapsburgs line, a dynasty where uncle-niece, first cousins and other consanguineous unions were prevalent. In many ways, Charles was the culmination of hundreds of years of inbreeding in a royal blood empire — thought to be perfect. In reality, the last Habsburgs were anything but perfect.

Charles II died prematurely aged 39 but not before his foolish behavior plunged his kingdom into chaos eventually leading to the War of Spanish Succession. This was the first world war of modern times with theatres of war in Spain, Italy, Germany, Holland, and at sea. It’s estimated the war resulted in 400,000 casualties. 

Here’s how one biography describes King Charles (Carlos) II:

“The Habsburg King Carlos II of Spain was sadly degenerated with an enormous misshapen head. His Habsburg jaw stood so much out that his two rows of teeth could not meet; he was unable to chew. His tongue was so large that he was barely able to speak. His intellect was similarly disabled. His brief life consisted chiefly of a passage from prolonged infancy to premature senility. Carlos’ family was anxious only to prolong his days and thought little about his education, so that he could barely read or write. He had been fed by wet nurses until the age of 5 or 6 and was not allowed to walk until almost fully grown. Even then, he was unable to walk properly, because his legs would not support him and he fell several times. His body remained that of an invalid child. The nature of his upbringing, the inadequacy of his education, the stiff etiquette of his court, his dependence upon his mother and his superstition helped to create a mentally retarded and hypersensitive monarch.”

Facial deformities, as well as a history of mental illness, run deep in the Habsburg family line. However, until now no study has confirmed that the distinct “Habsburg jaw” was the result of inbreeding.

Francisco Ceballos, is a geneticist who for the last couple of years has been studying genomic inbreeding in world populations. Ceballos and colleagues enlisted the help of 10 maxillofacial surgeons who were asked to use their expertise and judge facial deformity in 66 portraits of 11 Habsburg family members.

Many of these portraits are curated by some of the world’s foremost art museums, including the Prado Museum in Madrid and the Kunsthistorisches Museum in Vienna. The study only employed paintings where it has been historically confirmed that the authors had personally seen the individual portrayed.

Charles V, a Holy Roman Emperor and ancestor of Charles II of Spain. Credit: Wikimedia Commons.

The experts scored each family member on their degree of mandibular prognathism and maxillary deficiency (a prominent lower lip and an overhanging nasal tip respectively). Meanwhile, the researchers calculated the inbreeding coefficient of the Habsburg kings and queens by examining genealogical databases, which included more than 6,000 individuals belonging to more than 20 generations.

“Our main objective of our research is to understand the genetic architecture of the human face. And for that, we use the Habsburg as true human genetic laboratories. The main question is if the “Habsburg face” is affected by the inbreeding they practiced. The “Habsburg jaw” is not just a prognathism problem but the combination of two “issues”: mandibular prognathism (MP) and maxillary deficiency (MD). That is why it should be named “Habsburg face”. By studying the effect of inbreeding over those traits we can learn a lot about their genetic architecture: Is it ruled by a few genes with strong effects? Or by a plethora of genes with mild effects? Are these effects recessive or dominant?” Ceballos told ZME Science.

According to the results, Mary of Burgundy, who married into the family in 1477, showed the least degree of both traits. The most pronounced prognathism was found in Philip IV, King of Spain and Portugal, who ruled from 1621 to 1640. The greatest degree of maxillary deficiency was found in five family members: Maximilian I (regent from 1493), his daughter Margaret of Austria, his nephew Charles I of Spain, Charles’ great-grandson Philip IV and the last in the Habsburg line, Charles II.

Philip IV of Spain (1605-1665). Credit: Wikimedia Commons.

The researchers analyzed the effects of inbreeding over the degree of mandibular prognathism and maxillary deficiency by employing statistical methods, finding that the two traits share a common genetic basis.

“The ‘Aha!’ moment was when we discovered that the MD is affected indeed by inbreeding, and that the Habsburg face is indeed related to their consanguinity. This is the first time that science backs up this statement,” Ceballos told me over e-mail.

It is yet unclear, however, how facial deformity and inbreeding are connected. That’s not to say that there aren’t any possible explanations. Mating between relatives is known to increase the odds of offspring inheriting identical forms of a gene from both parents (genetic homozygosity). This can reduce an individual’s genetic fitness. Charles V, for instance, was believed to suffer from at least two conditions caused by recessive mutations in different genes: pituitary hormone deficiency (which can result in infertility) and distal renal tubular acidosis, a cause of kidney failure.

“While our study is based on historical figures, inbreeding is still common in some geographical regions and among some religious and ethnic groups, so it’s important today to investigate the effects,” lead researcher Professor Roman Vilas from the University of Santiago de Compostela said in a statement. “The Habsburg dynasty serves as a kind of human laboratory for researchers to do so, because the range of inbreeding is so high.”

In the future, the research team plans on investigating the genetic architecture of the human face more broadly by including other royal dynasties.

“We were able to answer many questions, like the heritability of these traits and other insights of their genetic architecture. Also we are using these dynasties (not just the Habsburgs) to get insights into the genetics of fertility, life expectancy, etc. We also calculated the inbreeding coefficient of every royal family of Europe until nowadays,” Ceballos said.

“It is possible to study the genetics of the human face: the mirror of the soul by using the information we have about our European royals. As we have shown in different papers, these royal dynasties are a magnificent genetic human laboratory, where science, history and art come together. We can learn a lot of modern genetics from them, even without having any single molecule of DNA,” he concluded.

The findings appeared in the journal Annals of Human Biology.

Neanderthal extinction could have been driven by inbreeding, demographic issues — not modern humans

Small populations and inbreeding may have driven the Neanderthals extinct, new research suggests.

Neanderthals disappeared sometime around 40,000 years ago, about the same time as modern humans began moving into Europe and the Near East. Because of the timing, it’s often held that modern humans helped drive our ancient relatives extinct, but this theory hasn’t been confirmed or infirmed up to now.

A new study looked at the population dynamics of Neanderthal groups in a bid to gain insight into their extinction. Through the use of demographic modelling, the team tried to establish if internal factors helped drive the Neanderthals out of history — and whether they were headed for collapse on their own, without the ‘help’ of modern humans.

Family ties

“Our results indicate that the disappearance of Neanderthals might have resided in the smallness of their population(s) alone,” the paper’s abstract reads. “Even if they had been identical to modern humans in their cognitive, social and cultural traits, and even in the absence of inter-specific competition, Neanderthals faced a considerable risk of extinction.”

The team used data from hunter-gatherer populations today as a guideline for their modeling efforts. After observing how these groups operate, the team developed population models for Neanderthal groups of various initial sizes: 50, 100, 500, 1,000, and 5,000 individuals.

The team then mixed in the effects of inbreeding, Allee effects (where reduced population size negatively impacts individuals’ fitness), and random demographic fluctuations (caused by shifting births, deaths, and sex ratios) into their simulated societies and observed the results. What they wanted to determine was if these factors were enough to drive the communities to extinction over a 10,000-year period.

Inbreeding alone was likely not enough to drive most Neanderthals to extinction. The team notes that it only led to the collapse of the smallest population modeled for the study. However, Allee effects could cause the extinction of populations up to 1,000 individuals strong when 25% of fewer Neanderthal females gave birth within a given year (the team reports that this is a common birth rate in hunter-gatherer societies today. When all three factors were together (inbreeding + Allee effects + demographic fluctuations), all the populations modeled in the study died out within 10,000 years.

Being based on computer models — which themselves are based on modern human hunter-gatherers — means that the findings should be taken with a grain of salt. While the models can’t account for everything, they do give us a general idea of what was happening to the Neanderthals at the time, the team reports.

It’s possible that the encroachment of modern humans impacted the Neanderthals in ways that promoted inbreeding and subsequent Allee effects, which obviously could not be accounted for by the models. However, even in the absence of modern humans, Neanderthals were headed to extinction due to their demographic issues, according to the findings.

The paper “Inbreeding, Allee effects and stochasticity might be sufficient to account for Neanderthal extinction” has been published in the journal PLOS ONE.