Ever notice the "Habsburg jaw"? The distinct protrusion may have been caused by inbreeding—or so says a new study that revisits the topic of how the ruling family went extinct, LiveScience reports. "The Habsburg dynasty was one of the most influential in Europe, but became renowned for inbreeding, which was its eventual downfall," lead author Roman Vilas says in a statement. "We show for the first time that there is a clear positive relationship between inbreeding and appearance of the Habsburg jaw." The researchers focus on the dynasty's Spanish rule, which began in 1496 and ended when Charles II—plagued with terrible health, likely from inbreeding—was unable to produce an heir and died in 1700.
Based on their family tree, Spanish dynasty members had an average inbreeding coefficient of .093—pretty high compared to a child of two first cousins (.0625) or, say, England's Prince Charles (.004). Vilas and his team also had surgeons look at 66 portraits of 15 Habsburg members for jaw protrusion and other facial deformities. Conclusion? The big jaws occurred more often in those with higher coefficients. In a sad detail reported by the Smithsonian, it was said Charles II swallowed "all he eats whole, for his nether jaw stands out so much, that his two rows of teeth cannot meet." Vilas admits this needs more study, but says the Habsburgs are a "laboratory" for the effects of inbreeding, which remains common in "some geographical regions and among some religious and ethnic groups." (Read more inbreeding stories.)