Zombies abound in nature: Viruses and parasites can cause real-world zombification

Far from mere fiction, the animal world is full of examples of actual "zombies" — depending on your definition

By Troy Farah

Science & Health Editor

Published October 30, 2022 2:00PM (EDT)

Zombie hand emerging from the ground (Getty Images/Marc Mateos)
Zombie hand emerging from the ground (Getty Images/Marc Mateos)

One of the most influential texts of the 19th century, "Frankenstein; or, The Modern Prometheus" is widely regarded as one of the first true science fiction novels. The book's Gothic author, Mary Shelley, was keen to the cutting edge science of her time, inspired in part by misinterpretation of galvanism, which is electricity produced by chemical action, causing behavior like muscle contraction, for example.

The term's namesake, Luigi Galvani, believed that galvanism confirmed his theory of a form of energy called "animal electricity" that gives living things their life force. He demonstrated this by electrocuting dead frog legs and watching them twitch. Shelley was inspired by these experiments, weaving it into her story of Frankenstein's creature made from a potpourri of corpses.

Since then, animal electricity has since been discarded as a scientific concept. But the idea of reanimating the dead hasn't. In the 2020s, zombie stories and cinema still abounds; and the Silicon Valley tech elite, among others, are obsessed with the idea of being reanimated after death

It seems that some tropes never die. But is there actually any science to the notion of a zombie, something that lives on or reanimates itself after death? 

Depending on your definition of zombie, it appears there is some truth to the concept in nature. Take for example the zombie-ant fungus (Ophiocordyceps unilateralis), which targets foraging ants, hijacking their tiny nervous systems. If an ant becomes infected with the spore of this fungi, it will begin acting strange. It will seek out a more humid microclimate that helps the fungus to grow, climbing a few inches off the ground where it will clamp down on a leaf or blade of grass, then wait to die. Several days later, the fungus will erupt from the bug like the Chestbursters in "Alien," spreading spores to ensnare more bugs. A true zombie in nature. 

But there are countless other examples of zombification in the real world as well. To learn about the real science of zombies, Salon spoke to Athena Aktipis, an associate professor at Arizona State University's department of psychology. Alongside Dave Lundberg-Kenrick, she also co-hosts the podcast Zombified, which is not a George A. Romero fan club but rather a science education stream that aims to explain "why zombification happens, why we are susceptible to it, and what we can do about it."

This interview has been condensed and lightly edited for clarity.

Let's start with something basic. What initially sparked your interest in zombies?

Many people are surprised to learn that I'm actually not a zombie movie fanatic in general. What attracted me to zombies was their potential as a tool for education and learning, because they're just kind of these weird, compelling entities that can be metaphors for a lot of things. But there's actually a biological realism to zombification and many different ways that organisms can hijack each other.

With drugs [produced by plants], for example, that's actually about the interaction that organisms are having with each other through these chemical signals. A lot of organisms evolved to produce chemicals that change the way that the brain of other organisms function. So there are many sort of intuitive pharmacologists that are just organisms evolving to do stuff that manipulates the brain chemistry of other organisms.

So when we're talking about zombies, how literal are we getting? Or when we're talking about this in the scientific realm, is it just metaphorical?

So it's both. There are real life zombies in the biological world: organisms whose body, brains and behavior are hijacked by other organisms. Full-stop, completely hijacked. And there are degrees of that. So you can have everything from cordyceps fungus completely overtaking all of the ability of an insect to control its fate. Or you could have more subtle influences, like if you're in a relationship with another human being. It could be a romantic relationship or a parent-child relationship. If you're being conditioned to behave in a certain way, that's a certain kind of zombification.

So that doesn't feel as intense as like, oh, a fungus is like completely taking over the function of your body, and 100 percent hijacking you. But it exists on a spectrum of real life zombification but then we also have more metaphorical zombification.

But there's a reality of brains and body's behavior getting hijacked by things that are not you. And so if that's your definition of a zombie and zombification, then it's all over the place in the natural world. And we humans are not excluded from that. We're vulnerable to being zombified as well.

When you talk about stuff like cordyceps fungus I guess I thought it was more of like a metaphor for that insect-fungus relationship. It's not an actually a dead thing that comes back to life. But you're talking more about how it's like this hijacking of the brain. Can we talk about how that happens?

Yeah, there's so many different kinds of zombies in the movies. Some of them, they're dead, they're buried, they come out of the grave. Others, you get bit and then you get turned into a zombie. So that's more of like an infection kind of zombie.

The original idea of like a zombie that's buried and then comes back to life comes from Haiti. These practices where people would be given pufferfish poison, and it could slow down their heart rate so much that they seem dead but they're breathing. So like, sometimes they would be treated as dead, and then they would, you know, quote, unquote, come back to life, but have severe impairments at that point.

The idea is that this was potentially used as a way of controlling slaves back in Haiti. So the idea of the zombie has historical roots that also are quite real in terms of there's this pufferfish toxin that does severe neurological damage and can create behaviors that seem zombie-like. Humans trying to control other humans is both the literal and the metaphorical aspect of zombies.

I'm really interested in this single-celled parasite called Toxoplasma gondii that turns rats into zombies. Can you explain what that is? I guess it's spread by cat feces?

Yeah, it's this organism whose lifecycle depends on parasitizing other organisms, and it can infect pretty much all mammals. It's most well known in cats, but humans can be infected by it, even marine mammals can be infected by it.

If you're a rat, and you get infected with it, it makes it so that cat urine doesn't smell bad. In fact, it smells good. It's sexually arousing to the rodents, and makes them approach the territory of cats, which makes it much more likely that they'll get consumed by the cat, which then perpetuates the Toxoplasma gondii.

Obviously, [the parasite] is not consciously doing any of this, it just evolved to do it. Because that allowed it to perpetuate itself. A lot of the sort of lessons around zombification is you don't need for there to be intention for really deep manipulation to be happening, because natural selection will favor organisms that are good at surviving, replicating, transmitting, and making it on to the next generation, regardless of the means.

People can be infected by Toxoplasma gondii. And there's been some work showing that there's greater susceptibility to some mental disorders, especially if your mother was infected with it while you were in the womb. Schizophrenia, for example. There have also been a number of studies looking at changes in sort of personality and behavior with Toxoplasma gondii infection. There's some controversy around those, about whether the methods were sufficient to rule out alternative hypotheses. But there are some studies that show that there's differences in risk-taking behavior and some differences in personality with different effects, depending if you're male or female.

So it's likely that it's having some effect on humans, but I think that the research is still kind of early as to what exactly the nature is of those effects. Like, there's no evidence that if you're infected by Toxoplasma gondii, that makes you more likely to be a person with too many cats in your house. I mean, it'd be cool if that was the case. But I don't think that anybody's established that yet.

Tell me about this idea you wrote about with Joe Alcock in The Conversation about how SARS-CoV-2, the virus that causes COVID, can also sort of turn people into zombies in a way.

So the basic idea is that if you look at how COVID affects physiology, it actually interferes with pain perception. And so people will feel really good early on when they're infected. My colleague Joe Alcock is an emergency room physician and we use this idea that if you're infected, you might not be the undead, but you're the unsick. Like, you're actually sick, your body is suffering from this virus, it's doing a lot of damage, but it's interfering with your pain perception, so you feel good.

So you actually aren't engaging in the sickness behavior that is typical, which would be more likely to keep you home and rest. And not just help you recover from the virus, but also would protect others. So by interfering with that pain perception, the virus is essentially putting off the negative effects, the damage that it's doing to the body in order to keep the organism moving around. And probably transmitting the virus and also keeping the immune system more compromised, because if you're like, "Oh, I feel great, I'm gonna go do stuff," then your body isn't investing as much in immune function. There are also a lot of people who are just completely asymptomatic when they have COVID.

That whole aspect of a COVID hasn't been studied, in my opinion, in the kind of depth that it should. And I think that's a strategy that is not uncommon when it comes to infectious agents that can benefit from their hosts being up and around. Sexually transmitted infections will also often have these kinds of features where they actually don't have negative effects on the host. Because if they did, then they would be less likely to transmit.

So in my opinion, there's a lot of work that can and should be done around understanding these dynamics [of zombies], because it's really, really relevant to the new era that we're in, which is an era of pandemics.

By Troy Farah

Troy Farah is Salon's science and health editor specializing in drug policy and pandemics.

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