The Science of Zombies

I am a fan of zombies. George Romero zombies, Robert Kirkman zombies, fast zombies, zombie comedies (‘zom-coms’), zombie romantic comedies (‘zom-rom-coms’) — I can’t get enough.

So imagine my delight in coming across not just one, but two scientific articles about zombies. Both of these papers investigate the real-life phenomenon of zombies in Haiti, where the idea of the zombie originated. The traditional explanation for zombies is sorcery. The Vodun religion (also known as Voodoo) makes a distinction between different elements of a human being. There is the corps cadavre (the physical body), the gwoban anj (the animating principle), and the ti-bon anj (agency, awareness, and memory).

Haitian zombies aren’t really undead. They are the result of a sorcerer taking the ti-bon anj of the victim, leaving a passive and easily-controlled body. These zombies are then believed to be used as free labor on Haitian plantations. Haitian zombies are easily identified by the community. They cannot lift up their heads, have an empty staring expression, and have limited and repetitive speech.

Poisoning was one theory to account for zombification, and in the early 1980s, anthropologist and ethnobotanist Wade Davis traveled to Haiti to investigate. He interviewed Vodun sorcerers and obtained samples of a white powder called coupe poudre that they used to zombify their victims. Analysis of the samples revealed a number of pharmaceutically active ingredients, including cane toad (Bufo marinus) toxins, an irritant produced by a tree frog (Osteopilus dominicensis), and tetrodotoxin, a neurotoxin produced by puffer fish and other marine animals.

Davis hypothesized that the irritant causes small wounds on the skin of the victim, through which the tetrodotoxin enters the bloodstream. The potent toxin can kill by paralysis, but sub-lethal doses result in a significant reduction in heart rate and metabolic activity. Victims, completely paralyzed but fully conscious, are pronounced dead and buried. After a few days, the sorcerer returns and claims the body. The victim is kept enslaved in a permanent state of delirium and disorientation with more drugs, likely containing atropine and scopolamine, toxins with hallucinogenic properties derived from the plants Datura stramonium and Datura metel. In Haiti, both of these plants are known as the “zombie cucumber.”

Recently, scientists publishing in the journal Evidence-Based Complementary and Alternative Medicine revisited Davis’ zombie potions, analyzing the chemical, biological, and pharmacological components of the powders to determine if tetrodotoxin really is the most important ingredient. They came to the same conclusion as Davis and identified four species of puffer fish as the reason behind the poison’s efficacy.

Pufferfish tetrodotoxin blocks sodium channels and prevents neurons from firing. People who ingest the toxin and don’t die within the first 24 hours typically survive, although they often fall into a coma-like state for several days. During this time, they may appear to be dead; reduced metabolic activity decreases the body’s need for oxygen, and the diaphragm muscles may be partially paralyzed, making breathing difficult to detect.

Tetrodotoxin is certainly a potent neurotoxin, but even Davis emphasized that the zombie powder is just one requirement for zombification. Equally important are cultural expectations involving the power of Vodun sorcerers and the effects of the powder, which are learned and ingrained in many parts of Haitian society.

In 1997, the medical journal The Lancet published a medical investigation into three “returned zombies” —individuals whom family members identified as having died and then returned, sometimes decades later, as zombies.

Doctors performed full medical exams on the zombies, including EEG and CT brain scans. The first subject had no neurological damage but was diagnosed with catatonic schizophrenia. The second subject did suffer from brain damage, probably due to lack of oxygen and untreated epilepsy. The last subject was diagnosed with a developmental learning disability, possibly fetal alcohol syndrome.

The most interesting finding came from DNA and fingerprinting tests that revealed that two of the zombies were cases of mistaken identity. They were not the dead relatives that the families identified.

It is unlikely that there is a single explanation for all cases of zombification. Poisoning by tetrodotoxin can cause symptoms typical of Haitian zombies, and it has been shown to be an ingredient in so-called “zombie powder.” But this study suggests a simpler answer: many zombie cases are mistaken identification of wandering mentally ill or neurologically injured people by grieving relatives, primed by their culture to accept the notion of zombies. The authors write that “People with a chronic schizophrenic illness, brain damage, or learning disability are not uncommonly met with wandering in Haiti, and they would be particularly likely to be identified as lacking volition and memory,” instantly recognized zombie characteristics.

Is the mystery of zombification solved? Sort of. It may be that there are as many types of real-life zombies as there are cinematic ones.


About Mary Bates

Mary Bates earned her PhD from Brown University studying bat echolocation. She is following her love of all things scientific to a career as a freelance science writer.

Posted on March 15, 2012, in Neurotoxins, Zombies. Bookmark the permalink. 1 Comment.

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