Quick: what was the first Science Fiction novel? I, Robot by Issac Asimov (1950)? The Time Machine by H.G. Wells (1895)? Journey to the Center of the Earth by Jules Verne (1864)?
The answer is “none of the above”– what is commonly agreed as the first Science Fiction novel was Frankenstein; or, The Modern Prometheus, published in 1818, written by Mary Shelly. Not quite what you’d think. Frankenstein, or, rather, Frankenstein’s monster, is a common figure around Halloween as the star of one of Universal’s classic monster movies. Frankenstein (1931) is a horror classic, and one of the first movies to be almost lying when it says “based on the novel by”. The novel is actually a lot darker, and more people die, but it also has a wildly different plot, so there’s that.
But still, since its inception, Science Fiction has been tied to horror and Gothic fiction. And historically, that makes sense– Science Fiction couldn’t really happen until science happened, and it also couldn’t really happen until the invention of the novel. Both of these things converged in the late-18th and early-19th centuries, during the Enlightenment. When you start learning the history of genres of literature, a lot of things begin to make sense.
Science Fiction is a very malleable genre. It goes with everything, like a good pair of jeans. Pair it with fantasy, and you have Star Wars. Pair it with historical fiction, and you have steampunk. Pair it with political thriller, and you have 1984, The Hunger Games, Brave New World, Fahrenheit 451— basically any dystopian fiction. Pair it with horror..?
Much like a good pair of jeans, when paired, Science Fiction is more of a secondary genre. It lends its aesthetics and settings, sometimes a plot device or two, in order to service the main genre. Superhero fiction, for example, uses element of Science Fiction, but is mainly Action-Adventure. When Science Fiction takes the lead, however, that’s when things get interesting– especially when it comes to horror.