Image taken from http://rachelannmason.com/Images/thumbnailimages/bigger%20images/habsburg%20jaw/hemisphere/ambassadors/chiefs/carlos/carlos.jpg
But I've got something exciting to write about now (at least exciting if you're me). It's a combination of history and biology, namely royal inbreeding leading to the extinction of the spanish Habsburg dynasty. These guys saw it as the ultimate marriage to get to say "I do" at the altar next to an uncle, a niece or a first-cousin. Of course, this genetic conservatism came with some setbacks. Instead of keeping it in the family (whatever it may be...royal strengh, blue blood, strange eating habits, and so on and so forth) this just brought up all those recessive traits that the founders of the dynasty might have carried around in their royal genome. So the Habsburgers included a few characters that got noteworthy names such as Joanna the mad, as well as yielding physical features such as a enlarged lower jaw.
The inbreeding came to its peak with Charles II of Spain. He was the son of the Habsburgers Mariana of Austria and Philip IV of Spain. These parents were not only related, they were uncle and niece, which meant that his grandmother was also his aunt. This might have been ok if not all other relatives (his parents, grandparents and backwards) were somewhat the result of interbreeding. A study was recently published showing that 24.5% of Charles II genome could have been made up by identical genes, which is basically what you can expect from a brother-sister interbreeding. Because of this genetic uniformity, Charles was mentally disabled as well as disfigured. He had ha hard time chewing (most likely due to the same condition that the earlier mentioned enlarged jaw) and some notes states that his tounge was so large that it was hard to understand what he was saying, and he frequently droowled. He didn't learn to speak until the age of four and he couldn't walk until he was about eight years old. Not what you'd expect of a godgiven royal dynasty. In addition, one of the many duties of being a king is to produce an heir, something that Charles never was able to due even though he tried with two wives, most likely due to impotence.
In short - if you ever had a delirious idea about your family's excellence in terms of heritability, then you should go wash your face with something cold and go for an unrelated spouse. Or else you may bring out genetic traits in your grandkids that will not look so good for the record.
Source:
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0005174
http://sciencenow.sciencemag.org/science-shots/
