In 1956, Hollywood set loose a film that defined an era–though what exactly it defined is open to interpretation. Invasion of the Body Snatchers is either a paranoid screed against the Red Menace or a paranoid screed against McCarthyism. Or it's a reasoned indictment of one or the other. Or a warning about the threat espoused by one or the other. It gets confusing. At any rate, this was the film that established the concept of pod people in the public imagination along with the image of a distraught Kevin McCarthy stumbling in the middle of a California motorway shouting, "You're next! YOU'RE NEXT!!"
Invasion of the Body Snatchers went on to become a classic of American cinema that was remade three times, ripped off too often to count, and gave the first logical explanation of why people in Minnesota act the way they do. Unfortunately, like many films, it has tended to overshadow the book upon which it was based; so much so that the latter had to change its title from The Body Snatchers to match its cinematic offspring.
If you've seen the film, The Body Snatchers (1954) by Jack Finney comes as a surprise. Even though the plot is basically the same, the approach is very different. Both recount the tale of Dr Miles Bennell, a physician in the small California town of Mill Valley (Santa Mira in the film). It's a quiet place off the main highway, but one with an increasingly menacing undertone as Dr Bennell is faced with a parade of patients claiming that their friends and relatives have been replaced by impostors. Dismissing it at first as some sort of mass hysteria, Bennell and a few of his friends piece together clues that lead them to the conclusion that the inhabitants of the town are being replaced by replicas generated by alien plants from outer space. If something isn't done, the town and eventually the entire human race will be replaced by the invaders
So far, so frightening, but where director Don Siegel emphasised the horror aspects of the plot, Finney took a more poetic tack. Siegel's invaders are marked by an ever mounting air of calculated menace as they gain the upper hand as more and more of the humans are disposed of. The invaders speak with loving relish at the opportunity of winning over another unwilling convert to their cause. In Finney's version, the alien invasion results in a stultifying effect on the community. Finney's replicas aren't fanatics, they're emotionless drones that spread like brambles that smother the native population. In the film, the replicants are monsters ever on the hunt for the Other. In the book, their increasing grasp is seen in the frustrations of salesmen who can't get the townsmen to buy anything except staples and restaurateurs who sit staring gloomily at empty dining rooms.
Eventually, we learn that the aliens are less conquers than nihilists. They don't want to possess the Earth; they merely wish to propagate themselves. This isn't good for mankind because their propagation involves eliminating competing lifeforms and that means every living thing on the planet. The replicas aren't intended to take over our way of life. They will merely die within five years, leaving Earth a lifeless world that the aliens will abandon. In a way, it's a rather despondent war.
Finney's novel is much more literary that the screenplay. It doesn't make you jump up and spill your popcorn the way the film does, but the horror of the situation is much deeper because you understand it better. The writing is smooth and draws the reader along, but it can't cover the holes that Finney fails to fill or the fact that his protagonists have a maddening tendency to ignore vital plot points simply because it would be inconvenient for Finney to explore them at that time. The other place where Finney doesn't match up to the film is that in the film, Dr Bennell is faced with real menace as he learns that he is the only human left in the town whereas in the book he discovers that many other people have survived the peril, which diffuses the drama.
In all, I would say that the book wins out in terms of style and a thoughtful plot that in some ways is as much an attack on Freud as anything else, but the film scores points for sheer impact. The nice thing is that this isn't a competition, so we can enjoy both on their merits.