Any book nerd will be happy to tell you that the book is always better. It doesn't matter if that book has been adapted into a movie, an HBO original TV series, or a hit Broadway musical: most die hard readers will jump to defend the book as the first and very best version of the story. But... what happens when the book is the adaption? Books aren't always original, but that's not necessarily a bad thing. Here are a few books that you didn't know were adaptations.
As the old saying goes, "good artists copy, great artists steal" (in the spirit of that quote, I can't quite figure out who said it first). Of course, adapting a story is not quite the same as stealing it—sometimes you even have permission. Many great writers over the years have "borrowed" stories from movies, plays, mythology, tv shows, and (naturally) other books. These aren't just those movie novelizations that you see in airports, either. Some of the all time classics of literature started out as a screenplay.
So, before you start any book vs. movie turf wars, you might want to double check and make sure that your favorite book isn't a secret adaptation:
1'On Beauty' by Zadie Smith
Zadie Smith's On Beauty is based on E. M. Forster's Howard's End, and yes, one of the main characters in her novel is named Howard. On Beauty departs from the plot of Howard's End a bit, and Smith adds a dimension of dealing with complicated racial identities to her characters. But the opening and closing scenes and most of the themes are nearly identical between the two novels.
2'Peter Pan' by J. M. Barrie
Yes, Peter Pan the book actually came after Peter Pan the play. J. M. Barrie first came up with the idea of a creepy little boy who never grew up in an early novel of his, adapted it into a full length stage play, and then gave Peter his own book. The story is very similar between play and novel, although the gender politics are a bit different in the stage play, where Peter is always played by a woman.
3'Beauty and the Beast' by Gabrielle-Suzanne Barbot de Villeneuve
Not only was Beauty and the Beast originally written by French novelist Gabrielle-Suzanne Barbot de Villeneuve, her version of the story was adapted from the Greek myth Cupid and Psyche. So... when you watch the Emma Watson film, you're watching a movie based on a movie based on a book based on a story by someone named Platonicus in the year 100 CE.
4'Fantastic Voyage' by Isaac Asimov
If you don't know Fantastic Voyage, then you probably know its basic premise from The Magic School Bus: a bunch of people are shrunk down and sent in a ship inside a human body. Famed sci-fi writer Isaac Asimov wrote the novel, but the screenplay for the movie version of Fantastic Voyage actually came first. Asimov only deigned to write a book based on a movie if he was allowed to go all out on the hard sci-fi scientific accuracy, so you might want to have a biology textbook and WebMD handy for this one.
5'Madame Bovary' by Gustave Flaubert
Madame Bovary is actually an adaptation of the literary classic Don Quixote, despite the lack of old men fighting windmills. In this updated version, a woman named Emma yearns for some kind of romantic excitement beyond her humdrum marriage, and goes questing in search of it (if you've read Don Quixote, you probably know where this is going).
6'His Dark Materials' by Philip Pullman
The name "His Dark Materials" is straight out of a Milton quote, because Pullman's series is actually an adaptation of Milton's Paradise Lost. In Milton's version, the story of Adam and Eve's fall from grace is a little more explicit, but all of the major plot points are still there in the His Dark Materials trilogy. Plus everyone has a fluffy daemon, which makes a theological epic much more fun.
7'2001 A Space Odyssey' by Arthur C. Clarke
The book and movie of 2001: A Space Odyssey were more or less created as the same time, so it's a little hard to say which is an adaptation of what (as befits a story as mind-bending as this one). There are a few differences between the versions, like changing Jupiter to Saturn or adding a whole lot more to H.A.L.'s backstory. It's safe to say, though, that the "greatest science fiction epic of our time" was always meant for both the page and screen.