It is alleged to have been derived through a female from the princely Polish family of Piasts, its Masovian branch. The deformation of lips is clearly visible on tomb sculptures of Mazovian Piasts in the St. John's Cathedral in Warsaw. However this may be, there exists evidence that the trait is longstanding. It is perhaps first observed in Maximilian I (1459-1519).Traits such as these that were common to royal families are believed to have been passed on and exaggerated over time through royal intermarriage which caused acute inbreeding.
Due to the large amount of politically motivated intermarriage among Habsburgs, the dynasty was virtually unparalleled in the degree of its inbreeding. Charles II of Spain is said to have had the most pronounced case of the Habsburg jaw on record. His jaw was so deformed that he was unable to chew.