We found out recently that if you try to leave a little kid in a graveyard¹ late at night, he'll freak out. Even if you offer to leave him a gun to protect himself. Why? It's because on some instinctual level, all humans know it's just a matter of time until the zombies show up.

Our culture is full of tales of the undead walking the Earth, from our religions to our comic books. But, some sort of zombie apocalypse isn't actually possible, right?

Right?

Guys?

Actually, yes. It's quite possible. Here's five ways it could happen, according to science.

Brain Parasites³

As seen in ...

Resident Evil IV

What are they?

Parasites that turn victims into mindless, zombie-like slaves are fairly common in nature. There's one called toxoplasmosa gondii that seems to devote its entire existence to being terrifying.

This bug⁴ infects rats, but can only breed inside the intestines⁵ of a cat. The parasite² knows it needs to get the rat inside the cat (yes, we realize this sounds like the beginning of the most fucked-up Dr. Seuss poem ever) so the parasite takes over the rat's freaking brain, and intentionally⁶ makes it scurry⁷ toward where the cats hang out. The rat is being programmed to get itself eaten, and it doesn't even know.

Of course, those are just rats, right?

How it can result in zombies:

Hey, did we mention that half the human population on Earth is infected with toxoplasmosa, and don't know it? Hey, maybe you're one of them. Flip⁸ a coin.

Oh, also, they've done studies and shown that the infected see a change in their personality and have a higher chance of going batshit insane.

Chances this could cause a zombie apocalypse:

Humans and rats aren't all that different; thats why they use them to test our drugs. All it takes is a more evolved version of toxoplasmosa, one that could to do us what it does to the rats. So, imagine if half the world suddenly had no instinct for self-preservation or rational thought. Even less than they do now, we mean.

If you're comforting yourself with the thought that it may take forever for such a parasite to evolve, you're forgetting about all the biological weapons programs around the world, intentionally weaponizing such bugs⁹. You've got to wonder if the lab workers don't carry out their work under the unwitting command of the toxoplasmosa gondii already in their brains. If you don't want to sleep at night, that is.

You may be protesting that technically¹⁰ these people have never been dead and thus don't fit the dictionary definition of "zombies," but we can assure you that the distinction won't matter a whole lot once these groaning¹¹ hordes¹³ are clawing their way through your windows.

As seen in ...

The movie The Serpent and the Rainbow, the upcoming Resident Evil 5 video game.

What are they?

There are certain kinds of poisons that slow your bodily functions to the point that you'll be considered dead, even to a doctor (okay, maybe not to a good doctor). The poison from fugu (Japanese blowfish) can do this.

The victims can then be brought back under the effects of a drug like datura stramonium (or other chemicals called alkaloids) that leave them in a trance-like state with no memory, but still able to perform simple tasks like eating, sleeping, moaning and shambling around with their arms outstretched.

How it can result in zombies:

"Can?" How about "does."

This stuff has happened in Haiti; that's where the word "zombie" comes from. There are books about it, the most famous ones by Dr. Wade¹⁴ Davis (Passage of Darkness and The Serpent and the Rainbow). Yes, the movie The Serpent and the Rainbow was based on this guy's actual science stuff. How much of it was fact? Well, there was that one scene where they strapped¹⁵ the guy naked to a chair and drove a huge spike¹⁶ through his balls. We're hoping that part wasn't true.

What is definitely true is the story of Clairvius Narcisse. He was a Haitian guy who was declared dead by two doctors and buried in 1962. They found him wandering around the village 18 years later. It turned out the local voodoo priests had been using naturally occurring chemicals to basically zombify people and putting them to work on the sugar plantations¹⁷ (no, really).

So, the next time you're pouring a little packet of sugar into your coffee, remember that it may have been handled by a zombie at some point.

Chances this could cause a zombie apocalypse:

On the one hand, it's already fucking happened! So that earns it some street cred right off the bat. But, even if some evil genius intentionally distributed alkaloid toxins¹⁸ to a population to turn them into a shambling, mindless horde¹², there is no way to make these zombies aggressive or cannabalistic.

Yet.

The Real Rage Virus

As seen in ...

28 Days Later

What is it?

In the movie, it was a virus that turned human beings into mindless killing¹⁹ machines. In real life, we have a series of brain disorders²⁰ that do the same thing. They were never contagious²¹, of course. Then, Mad Cow Disease came along. It attacks the cow's spinal²² cord and brain, turning it into a stumbling, mindless attack cow.

And, when humans eat the meat ...

How it can result in zombies:

When Mad Cow gets in humans, they call it Creutzfeldt-Jakob disease. Check out the symptoms:

* Changes in gait (walking)

* Hallucinations

* Lack of coordination²³ (for example, stumbling and falling)

* Muscle twitching²⁴

* Myoclonic jerks or seizures²⁵

* Rapidly developing delirium²⁶ or dementia

Sure, the disease is rare (though maybe not as rare as we think) and the afflicted²⁷ aren't known to chase after people in murderous mobs. Yet.

But, it proves widespread brain infections of the Rage variety are just a matter of waiting for the right disease to come along.