Interesting essay, especially since it provided me with the Gerard Jones links, but it mostly makes me ask: is Alien really a "horror" film?

What exactly is the difference between sci-fi and horror, anyway? When Mary Shelley wrote Frankenstein it was probably considered sci-fi, because there was nothing in the science of the day to refute it. By the time they got around to making movies out of it, it's genre had shifted to "horror" simply because it's science was so outdated as to now be the stuff of fantasy. But really, the story didn't change.

Will the same thing happen to Alien?