King Sebastian of Portugal

Sebastian of Portugal was born on 20 January 1554, the feast of Saint Sebastian, the only child and heir of John Manuel, Prince of Portugal, and his wife, Joanna of Austria.

Sebastian of Portugal (1554)

He grew up and became a half-way decent king. He was great if you were Catholic, and awful if you were anything else, but it was because he was trying to HELP you realize how wrong you were to not be Catholic. He did a lot of great things for the structure of the Portuguese legal and educational system, and was generally beloved of his subjects because he really cared about being good monarch.

What fascinates me about Sebastian, however, is the fact he was more related to himself than a pure-bred Pekinese dog in Victorian England. Seriously, he was his own first cousin and uncle.

An individual has 8 great-grandparents and 16 great-grandparents, and ideally these people are all unrelated (except by marriage). At the very least, they tend to be different people. Not so in Sebastian’s case.

He only had 4 great-grandparents because his parents, who were double-first cousins, had the exact SAME GRANDPARENTS. His great-grandparents on both his mother and his father’s side of the family were King Manuel I of Portugal & Maria of Aragon and King Philip I of Castile & Joanna of Castile.

The plot thickens and the genetic diversity thins. Those great-grandparents were ALSO cousins. Thus, King Ferdinand II of Aragon and Queen Isabella I of Castille were 50% of Sebastian’s ancestors all by themselves. The other 50% wasn’t what you’d call ‘diverse’ either. 25% of his genetic great-grandparents were Ferdinand, Duke of Viseu and Beatrice of Portugal while the remaining 25% were Maximilian I, Holy Roman Emperor and Mary, Duchess of Burgundy.

His family tree didn’t BRANCH.

Untitled drawing

This sort of cousin intermarriage would eventually lead to the so-called “Habsburg Jaw”, an extreme form of mandibular prognathism, passed down from Emperor Maximillian I to his descendants.

One of the the most famous sufferers was Charles II of Spain, “the last Spanish Habsburg, was feeble-minded and physically deformed as a direct result of his limited gene pool. His ancestor, Joanna of Castile, actually appears in his family tree no less than fourteen times because of first and second cousins intermarrying. It is said that Charles II’s genetic makeup was more muddled than it would have been if his parents had been brother and sister … he could not chew his food and that the size of his tongue caused him to drool significantly.”

Really, if you think about it, King Sebastian got off lightly.

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