<P> In 1846, Massachusetts Governor George N. Briggs appointed a commission to study "idiots" in the state, and this study implicated cousin marriage as responsible for idiocy . Within the next two decades, numerous reports (e.g., one from the Kentucky Deaf and Dumb Asylum) appeared with similar conclusions: that cousin marriage sometimes resulted in deafness, blindness, and idiocy . Perhaps most important was the report of physician Samuel Merrifield Bemiss for the American Medical Association, which concluded cousin inbreeding does lead to the physical and mental depravation of the offspring ". Despite being contradicted by other studies like those of George Darwin and Alan Huth in England and Robert Newman in New York, the report's conclusions were widely accepted . </P> <P> These developments led to 13 states and territories passing cousin marriage prohibitions by the 1880s . Though contemporaneous, the eugenics movement did not play much of a direct role in the bans . George Louis Arner in 1908 considered the ban a clumsy and ineffective method of eugenics, which he thought would eventually be replaced by more refined techniques . By the 1920s, the number of bans had doubled . Since that time, Kentucky (1943), Maine (1985) (ETA: First cousin marriage is legal in Maine so long as the couple undergoes genetic counseling to ensure that--should the couple wish to have children - there is little - to - no risk of serious health defect), and Texas (2005) have also banned cousin marriage . The National Conference of Commissioners on Uniform State Laws unanimously recommended in 1970 that all such laws should be repealed, but no state has dropped its prohibition . </P> <P> Early Medieval Europe continued the late Roman ban on cousin marriage; under the law of the Catholic Church, couples were forbidden to marry if they were within four degrees of consanguinity . In the ninth century, the church raised the number of prohibited degrees to seven and changed the method by which they were calculated . Eventually, the nobility became too interrelated to marry easily as the local pool of unrelated prospective spouses became smaller; increasingly, large payments to the church were required for exemptions ("dispensations"), or retrospective legitimizations of children, in what amounted to a' protection racket' by the church . In 1215, the Fourth Lateran Council reduced the number of prohibited degrees of consanguinity from seven to four . The method of calculating prohibited degrees was changed also . Instead of the former practice of counting up to the common ancestor then down to the proposed spouse, the new law computed consanguinity by counting back to the common ancestor . In the Roman Catholic Church, unknowingly marrying a closely consanguineous blood relative was grounds for a declaration of nullity, but during the 11th and 12th centuries, dispensations were granted with increasing frequency due to the thousands of persons encompassed in the prohibition at seven degrees and the hardships this posed for finding potential spouses . After 1215, the general rule was that while fourth cousins could marry without dispensation, the need for dispensations was reduced . </P> <P> For example, the marriage of Louis XIV of France and Maria Theresa of Spain was a first - cousin marriage on both sides . It began to fall out of favor in the 19th century as women became socially mobile . Only Austria, Hungary, and Spain banned cousin marriage throughout the 19th century, with dispensations being available from the government in the last two countries . First - cousin marriage in England in 1875 was estimated by George Darwin to be 3.5% for the middle classes and 4.5% for the nobility, though this had declined to under 1% during the 20th century . Queen Victoria and Prince Albert were a preeminent example . </P>

How common was it for cousins to marry