page_title: Inbreeding
section_title: Royalty and nobility
hierarchical_section_title: Inbreeding / Humans / Royalty and nobility
context_page_description: Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity.
  Inbreeding results in homozygosity, which can increase the chances of offspring being affected by deleterious or recessive traits. This usually leads to at least temporarily decreased biological fitness of a population, which is its ability to survive and reproduce. An individual who inherits such deleterious traits is colloquially referred to as inbred. The avoidance of expression of such deleterious recessive alleles caused by inbreeding, via inbreeding avoidance mechanisms, is the main selective reason for outcrossing. Crossbreeding between populations also often has positive effects on fitness-related traits, but also sometimes leads to negative effects known as outbreeding depression.
context_section_description: Inter-nobility marriage was used as a method of forming political alliances among elites. These ties were often sealed only upon the birth of progeny within the arranged marriage. Thus marriage was seen as a union of lines of nobility, not as a contract between individuals as it is seen today.
  Royal intermarriage was often practiced among European royal families, usually for interests of state. Over time, due to the relatively limited number of potential consorts, the gene pool of many ruling families grew progressively smaller, until all European royalty was related. This also resulted in many being descended from a certain person through many lines of descent, such as the numerous European royalty and nobility descended from the British Queen Victoria or King Christian IX of Denmark. The House of Habsburg was infamous for its inbreeding, with the Habsburg lip cited as an ill-effect, although no genetic evidence has proved the claim.  The closely related houses of Habsburg, Bourbon, Braganza and Wittelsbach also frequently engaged in first-cousin unions as well as the occasional double-cousin and uncle–niece marriages. Examples of incestuous marriages and the impact of inbreeding on royal families include:
  In ancient Egypt, royal women were believed to carry the bloodlines and so it was advantageous for a pharaoh to marry his sister or half-sister; in such cases a special combination between endogamy and polygamy is found. Normally, the old ruler's eldest son and daughter (who could be either siblings or half-siblings) became the new rulers. All rulers of the Ptolemaic dynasty uninterruptedly from Ptolemy IV (Ptolemy II married his sister but had no issue) were married to their brothers and sisters, so as to keep the Ptolemaic blood "pure" and to strengthen the line of succession. King Tutankhamun's mother is reported to have been the half-sister to his father, Cleopatra VII (also called Cleopatra VI) and Ptolemy XIII, who married and became co-rulers of ancient Egypt following their father's death, are the most widely known example.
  In Europe, the House of Habsburg famously possessed the mandibular prognathism of the Habsburger (Unter) Lippe (otherwise known as the 'Habsburg jaw', 'Habsburg lip' or 'Austrian lip'"). This was typical for many Habsburg relatives over a period of six centuries. Due to multiple consanguineous marriages within the family, the condition progressed through the generations until the last Spanish Habsburg, Charles II of Spain (1661-1700), could not properly chew his food. Charles II had a large number of genetic, physical, intellectual, sexual, and emotional problems. His inbreeding coefficient was 0.254, equivalent to the offspring of brother–sister incest. His impotence/infertility led to the extinction of the (male) Spanish Habsburgs upon his death, triggering the War of the Spanish Succession, resulting in Spain's rule by the French House of Bourbon.
caption: Charles II of Spain. He is best remembered for his physical disabilities, believed to be the result of inbreeding.
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