THE jutting 'Habsburg jaw' - a facial deformity common to the European royal family of the same name - was the results of centuries of inbreeding, according to a new study.Generations of intermarriage secured the Habsburg dynasty's dominance over a vast European empire encompassing Austria and Spain between the 15th and 17th centuries. The 'Habsburg jaw' is a facial deformity common to the European royal family of the same name. Portrait of King Charles II of SpainHowever it also led to its decline when Charles II, the final Habsburg monarch, was unable to produce an heir.Until now, no research has been able to confirm that the Habsburgs' distinct chin was a result of inbreeding.Study leader Professor Roman Vilas said: "The Habsburg dynasty was one of the most influential in Europe, but became renowned for inbreeding, which was its eventual downfall."We show for the first time that there is a clear positive relationship between inbreeding and appearance of the Habsburg jaw." Scientists think the deformity was caused by centuries of inbreeding. Pictured is Philip IV, King of Spain, who is believed to have suffered from the conditionCredit: Getty - ContributorThe Habsburg family interbred in a bid to maintain power over a vast European empire between the 15th and 17th centuries. Pictured is a portrait of Charles II of Spain, 1693Who were the Habsburg family?Here's what you need to know...The Habsburgs are one of the most powerful families in European historyOf Austrian descent, they ruled much of central Europe during the Medeival and Middle AgesAt their height, the Habsburgs' empire encompassed Austria and Spain, the lower countries and much of South AmericaThe family famously interbred in order to keep power within the bloodlineThey thought marrying within the family would strengthen the royal bloodlineThis is thought to have passed multiple deformities on to each generation, including a jutting chin known as the Habsburg jawIn the end, inbreeding proved to be too much for the HabsburgsIt led to the family's decline when Charles II, the final Habsburg monarch, was unable to produce an heirUntil now, no research has been able to confirm that the Habsburgs' distinct chin was a result of inbreeding. Pictured is a portrait of the Duchess Mary of BurgundyCredit: Corbis - GettyThe researchers recruited ten specialist facial surgeons to identify the Habsburg jaw in 66 portraits of 15 members of the dynasty.Despite differences in artistic style, the portraits are characterised by a realistic approach to the human face.The surgeons were asked to diagnose eleven features of the Habsburg Jaw - or mandibular prognathism.They also identified seven features of maxillary deficiency, the most recognisable of which are a prominent lower lip and an overhanging nasal tip. Portrait of Ferdinand II of Habsburg, Holy Roman Emperor from 1619 to 1637Credit: Getty - ContributorThe portraits are hanging in some of the most prominent art museums in the world, including the Kunsthistorisches Museum in Vienna and the Prado in Madrid.The surgeons gave scores for the degree of mandibular prognathism and maxillary deficiency in each member of the Habsburg family.Mary of Burgundy, who married into the family in 1477, showed the least degree of both traits.The Habsburg jaw was most pronounced in Philip IV, King of Spain and Portugal from 1621 to 1640. Scientists analysed portraits of the family dating hanging in galleries across the globeCredit: Getty - ContributorPortrait of Mariana Of Austria in 1652Credit: Getty - ContributorMaxillary deficiency was diagnosed to the greatest degree in five members of the family: Maximilian I (regent from 1493), his daughter Margaret of Austria, his nephew Charles I of Spain, Charles' great-grandson Philip IV and the last in the Habsburg line, Charles II.Detecting a correlation between the two conditions, the researchers speculated that they shared a genetic basis.The extent of inbreeding was calculated from a large-scale family tree, including more than 6,000 individuals belonging to more than 20 generations.Researchers detected a strong relationship between the degree of inbreeding and the extent of the Habsburg jaw.The relationship to maxillary deficiency was also positive, but it was only statistically significant in two of the seven features diagnosed. The Habsburg jaw was most pronounced in Philip IV, King of Spain and Portugal from 1621 to 1640Credit: Getty - ContributorThe cause of the relationship between the inbreeding and facial deformity remains unclear.However, the scientists suggested mating between relatives increased the chance of offspring inheriting identical forms of a gene from both parents.This reduces someone's genetic fitness - meaning the Habsburg jaw should be considered a recessive condition.Professor Vilas added: "While our study is based on historical figures, inbreeding is still common in some geographical regions and among some religious and ethnic groups, so it's important today to investigate the effects."The Habsburg dynasty serves as a kind of human laboratory for researchers to do so, because the range of inbreeding is so high."Bones that may belong to Amelia Earhart sent for DNA testing as scientists plot second trip to find doomed pilot's plane In other news, the battered skeleton of a Scot found earlier this year may have been the remains of a brutally murdered royal.The lost Church of the Apostles where Jesus disciples once lived has finally been discovered, according to archaeologists.And, Europes oldest human footprints were found on a Norfolk beach in July and belonged to a mystery 950,000-year-old ancestor.What do you think caused the strangely-shaped jaws? Let us know in the comments!We pay for your stories! Do you have a story for The Sun Online Tech & Science team? Email us at tech@the-sun.co.uk