So I got my latest issue of Fortean Times (If you don’t know what it is, just trust me and get it), and among their media section was a blurb review of a film called “Inbred,” which sounds like your standard people get butchered by inbred clan of psychos. It’s really been a standard trope in Western horror for awhile – the terror of some separate, inbred group of maniacs out to kill you. The most prominent example of it is likely “The Texas Chainsaw Massacre” and it’s legions of illegitimate children, but you can easily find the roots in Lovecraft and the various swamp denizens, tribal cultists, and wizardly families who were both possessed of terrible knowledge and a lack of genetic diversity.
It’s not hard to determine why this is terrifying to people, and tells us a lot about humans: