Inbreeding and the Habsburg Jaw

The Habsburgs (sometimes spelled Hapsburg) were a dynasty of Europeans from the same family who ruled over Austria, Germany, the Holy Roman Empire, and eventually countries across the continent for two centuries in the Middle Ages. You can recognize them in portraits by their pronounced jaws, called the Habsburg jaw. You are probably familiar with the last of the Spanish Habsburgs, King Charles II, from a previous Neatorama post. He is shown at the left in the image above, with his father and great-uncle Philip IV on the right. Charles had the most tangled family tree you've ever seen, outside the pharaohs of ancient Egypt. He also had a very pronounced Habsburg jaw, and so many other physical problems he never produced a royal heir. Common sense would tell you that the inbreeding caused the Habsburg jaw to become more pronounced over generations, but now we have science.

A study in the Annals of Human Biology focuses on 15 members of the Spanish branch of the Habsburgs from different generations who had realistic portraits painted. First they gleaned information from the family tree and assigned each of the subjects an inbreeding coefficient. Charles' inbreeding coefficient was so high that he never had a chance. Then separately, they asked mouth and jaw surgeons to examine the portraits and rate facial features that would indicate mandibular prognathism (protruding jaw) and maxillary deficiency (sunken midface). Then they compared the data from the two studies to determine that the Habsburg jaw was, indeed, likely to be the product of inbreeding. Get the details on this study at Smithsonian.

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Being Scottish, my family has a genetic trait called the 'Kirk Thumb'. It looks like it has no pronounced knuckle below the thumbnail. The thumb is straight (up and down) looks sort of like a pencil. It's not a deformity, there is no restriction to the thumb. It just looks a bit different than most other peoples' thumbs.
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