This story contains spoilers for both the film and book versions of Annihilation.
Annihilation, Alex Garland’s bizarre, meditative, at times terrifying Ex Machina follow-up, is nothing like its source material. Jeff VanderMeer’s book is about... a lot. So is Garland’s movie. Oddly enough, the separate tracks they take end up at strikingly similar conclusions.
It might actually be a good idea to hold off on reading the novel of the same name (if you haven’t already) until after you’ve seen the movie, so that you don’t distract yourself by waiting for story beats that aren’t going to appear. There's no Crawler, no "strangling fruit" sermon written in lichens on a wall, no tower descending deep into the earth. The characters in the movie are given names instead of titles alone -- the biologist, the linguist, the psychologist -- and some who are dead at the beginning of the book end up alive at the end of the film. Rather than a skull-faced bear, the creature that hunts them in the book is a member of a past expedition, now more animal than human, transformed by Area X into a being whose chilling moans travel across the marshes in the dark of the night. Where the end of the book takes place at the top of a lighthouse, the climax of Garland’s film ends up at the bottom of one -- below one, in fact -- between Natalie Portman’s Lena and a humanoid double that looks like it stumbled off the set of Close Encounters of the Third Kind.
There are many examples of films that have little to do with the plot set down on the pages of the books they’re based on -- movies like Blade Runner and The Shining took plenty of liberties adapting text to screen, and created almost entirely new stories out of their source material. Garland never meant to adapt VanderMeer’s entire Southern Reach trilogy, which appeared in rapid succession and consists of Annihilation (February 2014), Authority (May 2014), and Acceptance (September 2014). Instead, he relied on the manuscript of the first book, the rights to which Paramount acquired in 2013, to form his script.