Paul J. Patterson, an assistant professor of English at Saint Joseph's University in Philadelphia, said the definition of what that "something" is that people fear depends on the social constructs of the time.
"The horror genre addresses our archetypal fears," Patterson said in a statement. "You can see throughout history how each generation has defined 'horror,' and it turns largely on the idea of something outside of our understanding threatening us."
Each generation's fears are embodied in these works, sometimes literally -- for example, in the form of zombies -- and other times invisibly, as unseen beings or unidentifiable people who can cause great harm.
Post-Sept. 11, 2001, films have seen a rise in torture-as-horror, likely because those who grew up around the rhetoric of the tragedy needed a way to comprehend it, Patterson said.
Diseases and outbreaks that attack whole populations are also popular in the horror genre, and they mirror the occurrences of stronger strains of influenza and the threat of biological warfare.
Past texts illustrated fears we now recognize as thematic: the rise of science versus religion; the recognition of sexual desire; and achieving immortality, Patterson said.
What's next in horror?
"We've seen the ascent of movies like "Saw and Hostel," and zombies -- death personified -- are back. But it's hard to say just what today's generation fears or will fear," Patterson said. "It may be technology going too far and taking us over, or the anonymity that technology affords backfiring on us. But whatever it might be, these books and films allow us to imagine or experience our desire to defeat what is hunting and haunting us on a splashy canvas."