Columns > Published on October 28th, 2013

It's Made Of SCIENCE: Zombies

When I decided to try writing a Halloween-themed science article, I admit I struggled a bit with choosing a topic. Science generally works against fear by making things more understandable. I suppose I could have written about the certain extinction of the human race, and how even if we are able to colonize other worlds and propagate across the stars, the final heat death of the universe will wipe out everything we have strived to achieve, rendering our accomplishments, our dreams, our philosophies null in an oblivion that is the definition of finality. I would write about how knowledge of this empty future results in inescapable nihilism, which calls into question the very meaning of existence in a universe where time is finite and the cessation of the human legacy is absolutely inevitable.

Then I thought, "Zombies. People like zombies. That'll work."

There are countless articles written about zombies. You'll find places that teach you how to make your own zombie survival kit, debates about which weapons you should pack, and ideas for the best places to congregate and hold out against the undead. This article doesn't really look at those aspects, but rather investigates the science behind the traditional depictions of zombies and how you might choose to realistically write about the brain-hungry monsters in your own work. This can be a big topic, so let's focus on the broader questions.

Can the dead be reanimated?

The body doesn't break down to bring about death as if it were on a timer. Death occurs because the body stops working the way it's supposed to work. Even though we are essentially bags of meat and blood, we can take a bit of punishment before dying, and so when we do die, it's because something that was required to keep us going is not working anymore. In order for the body to start working again, the part(s) need to work again.

Duh, right? Well, now think about zombies.

The brain is the most important part of the body as far as living goes. It controls our heart, our muscle movements, our ability to breathe, and so forth. The specialized cells (neurons) that make up the brain have some pretty severe drawbacks, such as the inability to store oxygen or glucose, both of which are absolutely necessary for the functioning of living cells. Without a steady stream of oxygenated, glucose-infused blood, the brain will die in about four minutes. When that happens, it's game over. The neurons are destroyed, and they can't be fixed or replaced.

Basically, our body is a life support machine for our brain. Our limbs get food so that we can feed our brain. Our blood delivers oxygen and nutrients to these limbs, as well as the brain itself. And so forth.

So when you watch a zombie movie and see the undead moving about with half their head missing, then that means they are impossibly coordinating movements using an organ that can't actually do what it's apparently doing. A zombie with its intestines hanging out is unable to process and absorb food, which means no glucose, which means no brain function. A zombie with thick, coagulated blood wouldn't be able to use that blood to supply the brain, which means that the brain isn't working. This would not only make zombies with these injuries impossible to scientifically justify, but it also means that shooting them in the head would be ineffective, since apparently the brain isn't actually doing anything anyway.

Take-away message: A zombie without eyes can't see, and a zombie without a functioning circulatory system can't walk, moan, or do any of the things zombies tend to do. So even if you miss the head shot, just wait for the sucker to bleed to death, and you should be good.

What about a zombie infection?

The more modern zombies tend to be the result of some sort of virus, which spreads through the population like a flu. This eliminates the magical hand waving of the Romero zombies, and terrifyingly enough, there are some examples in nature that give us a template for a potential zombie infection outbreak.

Viruses are essentially just genetic material wrapped up in a protein shell. The virus injects this genetic material into a cell, which hijacks the cell machinery and uses it to produce more viruses. In general, the best defense against them is our own immune system, which is why doctors will tell you to hang tough through a cold or flu.

Rabies has been popping up in contemporary zombie fiction. This is a virus that is transmitted through saliva, and can cause encephalitis, which is an inflammation of the brain. Brain swelling, you can imagine, will sometimes lead to erratic behavior. Rabies takes a few months to manifest symptoms after infection, and it's really easy to treat if the biting victim gets around to treatment within a week or so. While the virus can cause violent behavior, it doesn't necessarily result in humans trying to bite. Dogs and raccoons bite when aggressive, while humans will thrash and punch, which are notably poor ways of infecting others. All in all, it's not a particularly fine template for a zombie virus, but it is pretty frightening all the same.

I elected not to put a video of a rabies patient on here, as he is shown dying after horrendous suffering from the virus, but I think it's on YouTube if you are interested in seeing it.

Microorganisms like fungi and bacteria don't seem to come up much in zombie fiction, and I'm not sure why. Single-celled organisms don't necessary require a host cell to survive, which means that they can be smeared on a door handle and left to wait for the next potential host. They are a bit easier for us to kill with soap and antibiotics, but our overuse of products is producing some superbugs like MRSA, which has evolved a resistance to our treatment and prevention methods. Bacteria also have this neat ability called gene transfer, which allows them to absorb and integrate into their genome any random genetic material they happen upon. This would make it easy for, say, a mad scientist to add a rogue zombie sequence into a relatively harmless species of bowel flora.

The most horrifying zombie microorganism in nature (so far) is called Ophicordyceps unilateralis, which at the moment only affects ants. This bad boy infects the ant and takes over its behavior, forcing it to climb as high as it can go. Why? Because when the fungus kills the ant shortly thereafter, it'll cause a stalk to explode from the ant's head like a confused xenomorph chestburster, which will then blast spores back down on the ant's friends below. Oh, and yes, we are investigating the medical potential of this fungus, probably deep underground in some Umbrella laboratory.


A lesser-known possibility I wanted to mention are prions. Prions are infectious proteins, and don't contain any genetic material, but instead use a cell to build other prions directly. Think of it like a machine that was programmed to build other machines that are programmed to build other machines, with nobody behind the controls. We aren't very good at fighting prion disorders, and zombie writers should notice that prions tend to cause severe neurological disorders in humans. Creutzfeldt-Jakob disease (known incorrectly as the human form of Mad Cow) is a prion disorder, as well as kuru, a neurological disorder which was spread by cannibalism, specifically the eating of uncooked brains. Sound familiar?

How would a zombie infection be realistically transmitted?

Humans are good at not getting infected by things. We instinctively avoid things which could infect us (which is why decomposition, sewage, and poop smells bad to us). Even the act of scrunching up our faces and gagging in response to bad smells is our bodies attempting to force out potentially infectious material from our air passages. Our skin is nearly impenetrable to disease, and we have an incredibly elaborate immune system. Even ignoring medicine and society itself, it's actually fairly difficult to infect people with anything. It takes a subtle touch.

Traditional zombies spread infection in a way that is, well, not subtle. 

Zombie infection is pretty easy to identify, considering that the behavior is so erratic and animalistic. Look for the bloody guy growling hungrily at passersby. Easy identification means immediate isolation, which means no epidemic. The most dangerous real life infections are the ones that spread silently amongst people who don't even know they're infected, and this simply can't happen if the transmission method is "being snacked on by a screaming, decomposing crazy person."

The classic slow zombies from the Romero age would be cut down immediately, probably before the police even arrived, which is possibly the reason that zombies in Romero's universe weren't the result of infected wounds. Fast zombies might have a better chance at spreading the disease, but we're still talking about unarmed, deranged humans hunting other healthy, intelligent humans. Perhaps the slower, weaker individuals among us fall to the zombie infection, but that only results in slower, weaker zombies that can't physically match the people who survived. The chances of a worldwide epidemic through a biting-only mechanism is nearly nil.

So what would be more realistic? Think of the big scares we've had in the last few years with SARS and swine flu. The common thread we see is the airborne, invisible nature of the disease. This means that the disease can spread very quickly, and is tough to prevent even if the population is aware of it. To throw the world into a zombie epidemic, you would either need a very long incubation time that gives infected individuals a chance to move around and spread the stuff, or a massive exposure from bad guys looking to destroy the world.

It's this kind of dilemma that is likely the reason most zombie stories start in the middle of the epidemic, so if you want to dodge this issue, nobody is likely to think twice about it.

What else should I think about?

To avoid making this article too long, let me give you a few short tips you should consider when trying to write scientifically-accurate zombies.

  • Imagine what a zombie infection would actually do to a person's body. If it's shutting down the "thinking" part of the brain, then study animal behaviors as a template for zombie behavior. Monkeys eat, run, use basic tools, and keep themselves clean, so why couldn't a zombie?
  • Even amoebas can "learn" to avoid bad things, so zombies running headfirst into a machine gun nest isn't particularly realistic. You don't need to have a fully-functioning brain to understand how a door handle works. Think of zombies in terms of insane people, rather than stupid people, and you'll come up with something more likely to happen in the real world.
  • Think about group dynamics, and how zombies might interact with one another. Primitive humans had some sort of communicative abilities, as well as the ability to coordinate while hunting. Many zombie stories treat zombies as a mass of individuals, but in reality, they would be far more likely to coordinate in some fashion, as it would greatly enhance their potential of spreading the infection and/or eating brains.
  • As mentioned, the brain requires nourishment, so zombies have to eat. Since humans can get nourishment from plants, making food a zombie's primary drive would probably lead to zombies grazing in a field like cattle. Again, if you consider insanity as the primary effect of the zombie infection, then you're much more likely to end up with a zombie attacking people instead of house plants.

As a final note, don't be put off by this article if you find that your story doesn't work with the science. Zombie fiction generally gets a pass from scientific judgment, because most zombie stories aren't about the science of zombie infection. They're usually horror survival stories, and if that's the type of story you intend to tell, then by all means, use magical zombies if you want. Horror is about the unknown, and if the mechanism of your zombie infection isn't important, then there's nothing stopping you from creating a scary/silly/action-packed zombie story without the need for science.

PS: Because there is no serious scientific literature that deals with zombies, I elected to use my book link section to spotlight some zombie stories by our very own Rob Hart and Leah Rhyne. Show them some love.

Do you have an idea for my next science-themed article? I'm taking suggestions! Drop me some topics in the comments, and if I like it, and feel that I either understand or can research it well enough to explain it, your idea can be the next IMOS article. Also, feel free to call me out if you spot an error anywhere; I'd rather have a perfect article than a reputation for being perfect.

About the author

Nathan Scalia earned a BA degree in psychology and considered medical school long enough to realize that he missed reading real books. He then went on to earn a Master's in Library Science and is currently working in a school library. He has written several new articles and columns for LitReactor, served for a time as the site's Community Manager, and can be found in the Writer's Workshop with some frequency.

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