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.
In some countries outside that region, it is uncommon but still legal.
To many, Morgan included, cousin marriage, and more specifically parallel-cousin marriage, was a remnant of a more primitive stage of human social organization. Briggs appointed a commission to study "idiots" in the state, and this study implicated cousin marriage as responsible for idiocy.
In the past, cousin marriage was practised within indigenous cultures in Australia, North America, South America, and Polynesia.
Various religions have ranged from prohibiting sixth cousins or closer from marrying, to freely allowing first-cousin marriage.
The writings of Scottish deputy commissioner for lunacy Arthur Mitchell claiming that cousin marriage had injurious effects on offspring were largely contradicted by researchers such as Alan Huth and George Darwin.
In fact, Mitchell's own data did not support his hypotheses and he later speculated that the dangers of consanguinity might be partly overcome by proper living.