system
Given the following post, respond as if you're commenting on Reddit:
human
What is the origin of the southeastern US incest stereotype?
gpt
It's mostly an Appalachian stereotype.  Back before automobiles and paved roads, travelling from one valley to another could take vast amounts of time and effort. Combine that with a distrust of outsiders, and people tended to marry people who lived nearby, and those people were often relatives.   

It's important to remember that this sort inbreeding occurred in all parts of the world in the past, but because of the geography of the mountains, it lasted longer there.  It should also be noted that children of cousins don't actually have substantially greater genetic problems than those of strangers.  

I think the biggest factor in the negative perception of "hill billies" is a combination of localised cultural habits of isolated people which seem backwards to outsiders, along with a bit of a "brain drain". Those people with the most ability and drive would move out of their isolated hollows to more populous areas.