In 1555, Holy Roman Emperor Charles V announced his plans to abdicate, and his 28-year-old son, Philip II, became the king of Spain the following year. The throne was Philip’s natural—hereditary—right. The Habsburg dynasty, to which Charles and Philip belonged, had raised strategic matrimony to an art form, using marriage bonds among relations distant and close to seize control over much of Europe. Power came with a price, however: severe, recurring mental and physical problems. Charles’s mother was Joan the Mad; his son Philip was said to be “of weakly frame and of a gloomy, severe, obstinate, and superstitious character.” Philip’s descendant Charles II was 4 before he could talk and 8 before he could walk. He died in 1700, not yet 40, childless and sterile. Geneticists have calculated that he was more inbred than he would have been had his parents been siblings. After his death, the Spanish Habsburg dynasty collapsed, crushed under the weight of a heredity that as yet had no name.
The Weird, Ever-Evolving Story of Your DNA