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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), Maine (1985), and Texas (2005) have also banned cousin marriage.
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".
In the past, cousin marriage was practiced within indigenous cultures in Australia, North America, South America, and Polynesia.