people with common grandparents or people who share other fairly recent ancestors).
Opinions and practice vary widely across the world.
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National Conference of Commissioners on Uniform State Laws unanimously recommended in 1970 that all such laws should be repealed, but no state has dropped its prohibition.
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.
Only Austria, Hungary, and Spain banned cousin marriage throughout the 19th century, with dispensations being available from the government in the last two countries.
The 19th-century academic debate on cousin marriage developed differently in Europe and America.
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.
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. Since that time, Kentucky (1943) and Texas have banned first-cousin marriage and since 1985, Maine has mandated genetic counseling for marrying cousins to minimise risk to any of serious health defect to their children.
Writers such as Noah Webster (1758–1843) and ministers like Philip Milledoler (1775–1852) and Joshua Mc Ilvaine helped lay the groundwork for such viewpoints well before 1860.