This post originally appeared on the Zombie Preparedness Initiative website.

We know zombie’s, right? Zombies vary from depiction to depiction, but overall we know a few things about them:

1. They are the animated dead (or at least near enough that it makes no difference)
2. They are single minded in their desires
3. Their primary drive is to eat (or at least kill) non-zombie humans
4. Zombies are created by some virus, either mutated from an existing, natural virus or else created by someone (most likely the military and/or mad scientists)
5. Because of this, their bite (and possibly blood) will cause a person to turn into a zombie

Straightforward, right? Wrong.

The description above is a completely modern idea of zombies. Remember that a mere 10 years ago, the concept of zombies moving quickly was groundbreaking. Previously, zombies shambled around with their arms out, and at the time, that was scary enough. It turns out that zombies are the ultimate chameleons, changing to reflect whatever society as a whole currently fears.

Magic

Originally, zombies were created by magic or a curse, most often via Haitian voodoo. One such example of an early zombie movie is White Zombie (1932).

Voodoo zombies always have a controller or a master, and therefore most likely symbolize a fear of the loss of free will. Therefore, it should not be a surprise that these types of zombies were particularly prominent through the 1930’s and mid-1940’s, around the time of WWII. A world in which a charismatic leader could rouse unthinking masses to destroy life as we know it was entirely too real, the fear close to the surface.

One interesting thing to note about these original zombie movies is that zombies could not make other zombies; they could only be created by a zombie master. It’s interesting to think that the original idea of zombies didn’t include this core tenet of modern zombie movies.

Of course, magic or curse zombies have never really disappeared from the zombie movie genre. Although they have changed a bit over the years to stay current, it seems that these types of zombies are the most commonly reoccurring, appearing periodically through all the other time frames. I think that loss of free will is something that continues to be scary, particularly here in the hyper-individualist United States, where so many of these movies are created.

Some more recent examples include the classic Zombi II (1979), and more recently Dead Snow (2009) which brings nicely full circle back to WWII, with Nazi zombies.

Radiation

WWII culminated spectacularly with the nuclear bomb, giving all of humanity something new to be terrified of. Nuclear power fascinated us for many, many years (think of all the Godzilla movies from the ’50’s through the ’70’s).

This is  particularly interesting in this context, because radiation was the first to provide some other cause for zombies. So this is really the first time where we see someone starting to deviate from the “classic” voodoo zombie-myth, and it corresponds to the introduction of this new, scary thing that would dominate the cultural zeitgeist for years to come.

A perfect example is the classic Night of the Living Dead (1968), where the suspected cause of zombie creation was radioactive contamination from space probe from venus. Nuclear energy essentially was the new magic, because it was suddenly making so many things possible, but also had tremendously bad side effects. To my modern understanding of science, it makes absolutely no sense that “radiation from venus” could somehow turn people into zombies, but that’s kind of the point: as we learned more it became less plausible, less scary, and our zombie stories turned to other explanations.

Comets

During the 1980’s, there was a huge explosion in both the horror genre in general, as well as specifically apocalypse movies (see the three Mad Max movies between 1979 and 1985). Zombie movies, being the intersection of those two things, were no exception.

This explosion in interest in the imminent destruction of the world happens to coincide with the Cold War, when once again the imminent destruction of the world seemed a little too close for comfort. Just as with the previous two zombie movie categories, things are always a little more scary when they’re easily and realistically imagined.

However, easily the strangest explanation for the creation of zombies is the passing of a nearby comet. However, that was precisely the plot of Night of the Comet (1984). This would seem like a one-off oddity, but don’t forget about OTHER comet movies, such as Maximum Overdrive (1986). All of this focus on comets might seem weird, but consider the fact that in 1986, Halley’s comet was approaching Earth for the first time in 76 years. Even if people knew better, they were a little excited (and perhaps a little scared) about what this would bring.

Genetic Engineering

The early aughts brought us a much more modern fear with Resident Evil (2002). Between the first genome sequencing in 2000 and the stem cell ban lifted in 2001, genetic engineering was weighing heavy on our collective mind. The world was obviously ripe for a new kind of zombie.

Maybe it is because my wife works in genetics, but to me genetic engineering is some scary stuff. So I was actually quite surprised not to find more genetic engineering-related zombie movies. It just seems like it fits all of the patterns to what makes a good zombie.

Therefore, I have to assume that there would have been more of these types of zombie movies, except this fear was quickly outstripped by a new panic: infection.

In fact, even the Resident Evil franchise is more of an infection zombie, since, despite being developed in a genetic research facility, the zombies are created by the T-virus, and it can be passed via normal infection pathways, such as bites and scratches. Obviously that makes no sense from a genetic point of view.

Infection

Directly on the heels of Resident Evil came the SARS outbreak from 2002 to 2003, released almost simultaneously with 28 Days Later (2002). I don’t know if that was a coincidence, but I’m sure it didn’t hurt their box office. Once again we had a zombie movie echoing the very real fears of the time. The speed and deadliness of the SARS virus was eerily similar to the spread of the Rage virus, and therefore the extrapolation to the end of the world as we knew it was very easy to buy into.

To me, 28 Days Later really kicked off a new era of zombie movies. In addition to updating the genre to a relevant issue, viral infection, they also brought modern special effects and film making techniques to bear, as well as instituted “fast zombies” for the first time. Modern zombies were fast and aggressive, while still maintaining the “implacable horde” aspects of previous incarnations.

The Dawn of the Dead remake (2004) is interesting for the fact that it is a remake of an earlier movie, yet the cause of zombification is completely different than the original. If nothing else proves my theory, the fact that “updating” this movie including moving from radiation to viral infection is at least a point in my favor.

The new Dawn of the Dead codified a lot of what we now think of as zombies, to the point that a modern film maker would probably have trouble deviating much from the “rules” as they currently exist.

A viral infection feels “right” to me. It seems to make sense, or to offer as logical of an explanation as we can currently conceive of. But then again, I would say that, wouldn’t I? other people during other time periods would most likely have said the same about whatever the zombie explanation du jour was in their time (even comets and space radiation!)

Perhaps this would have been the end of the “infection age” of zombies, except along came the Swine Flu (H1N1) outbreak in 2009. As long as infection remains society’s number 1 fear, then it will remain the most popular method of zombification. And thus it continues, right up until present day, including “new classics” such as Walking Dead (2010) and World War Z (2013).

Sure there are deviations now and then (Zombieland (2009) even played to our fear of mad cow disease), but once again this almost proves the rule: zombie movies are quick to jump on that which frightens us most.

So what is the next big trend?

I don’t know, that’s a good question. If I knew the answer to that, I would be out pitching movie scripts, not researching old ones. My gut tells me infection is here to stay for some time yet. Most of the major trends had a good 20 year run, so I think we have some time yet before this one is played out. After that? Who knows. Perhaps a genetic’s scare will bring that back into prominence? A pollution catastrophe? Dark matter?

Regardless of the answer, we can rest assured that zombie movies will be right there to play on our fears and help us make sense of this crazy, crazy world.