Meg: “What about a sort of partial death? Zombies seem both alive and dead.”
Dr. Hafdahclass="underline" “Certainly, you can see a spectrum of death. People can have parts of the body die before the brain, like people with peripheral vascular disease where their blood vessels are too narrow to deliver blood and nutrients, so their limbs essentially die and need to be amputated (gangrene). Strokes are essentially partial brain death, where a part of the brain dies from a lack of blood flow, so whatever is controlled by that part of the brain dies (i.e., if they have a stroke in the speech center, they have slurred speech, if they have a stroke in the motor cortex, they develop weakness in half of their body, etc.).”
Kelly: “In Night of the Living Dead ‘fresh’ zombies have pale skin, walk stiffly, and sometimes moan. As a man of science, what advice would you have given George Romero about how a zombie should move or act?”
Dr. Hafdahclass="underline" “Think of living things like a car on the highway. In addition to the vehicle (the body), it needs two things to work: a driver (the brain) and a fuel source (food). Zombies would be no different! From the brain perspective, I think Romero did a very good job. In order for it to make sense I think the term ‘undead’ is the most proper term to use as we need to think of zombies partially living. Death is loss of integrated function of various organ systems, so brain death is when we lose that integrated function: the control center (i.e., the brain) can no longer control the body. Thus, if zombies are completely dead, the brain, by definition, could exert no control over the body in any capacity. Zombies would have no volitional movement so they would just lie there, which, of course, would not make for a scary movie. ‘Undead’ implies that death occurred, but there is some partial return to life, and the brain is able to regain control (at least partially) over the body again. I can imagine that a zombie, which has returned to partial living and has a partially functioning brain, probably has portions of its brain that still work but also parts that are very damaged. In humans, we can see what happens when small portions of the brain die, such as with strokes, multiple sclerosis, and other neurodegenerative diseases. One of the most interesting parts of brain physiology is that everything you do is controlled by a certain part of the brain. If the speech area of the brain dies, people lose the ability to talk and understand language. If the frontal lobe is damaged, people lose the ability to control their impulses, etc. I imagine a zombie has sustained profound damage to much of its brain, which would explain its loss of speech, impulse control, ability to feel pain, balance, etc. which I think Romero has perfectly captured with these stumbling, aphasic, primitive creatures in human bodies. I’m not sure why motor function is so much better preserved than other parts of the brain, but I guess that they have to move to be threatening!”
The brain.
Meg: “Do you think that’s why Romero chose to kill the zombies with a shot to the head? Because, supposedly, there is one part of the brain still functioning?”
Dr. Hafdahclass="underline" “I would suspect so! It seems to make sense that you kill the undead by severing the ‘control’ to make them dead again.”
Meg: “Or deader! Is that a word? More dead?”
Dr. Hafdahclass="underline" “Ha, yeah, exactly! So, going back to the car analogy, the other thing that zombies would need to ‘live’ would be a fuel source (and the ability to use that fuel source). Zombies are no different than any other animal. We need to consume food for energy in order to run the engine, and we all have a tremendous, overpowering primal urge to obtain energy. It makes sense that living humans would be a ripe source for energy! However, I would suspect that zombies would be omnivorous like us (i.e., can eat both animals and plants for food), so I suspect they are probably snapping apples off of trees when there are no humans around.”
Kelly: “That’s really cool! I wondered if there was any biological reason zombies would want to eat humans. And it’s funny to think of them eating other foods, too. Supposing there was a parasite or disease that brought upon zombies, how long would we have until the zombies crumbled? Could weeks or months go by like in the case of Dawn of the Dead?”
Dr. Hafdahclass="underline" “Great question. It would depend on answering this: could zombies actually digest humans for fuel? A human body can go about three weeks without food, so you would assume the same is true for zombies if they are following our rules. In order to stay alive, we need to turn the food we eat into a form of fuel we can use (glucose) through a process called digestion. This is a very complex process that involves a lot of things to work, including a stomach and at least the first part of the small intestine. Decapitated zombies would definitely be in trouble since they would need a mouth, but I think most zombies could still do this. Zombies would then need to be able to burn the fuel for energy. Our bodies do this through aerobic respiration, in which glucose and oxygen are combined to release energy. That energy is used to make muscles contract, keep skin intact, make the heart pump, etc. However, one glance at a zombie tells us that this would not happen. Despite their decomposing skin and no need for working hearts or lungs, most zombies are clearly ‘living’ longer than three weeks (though, if I recall, the film 28 Days Later (2003) adheres to this rule). Thus, zombies clearly must have some other process that lets them harness energy, or at least slows down the decaying process. Perhaps part of the science of the zombie virus is that it allows them to make energy without oxygen?”
Meg: “Hmm, so it sounds like zombies might be starving, giving us maybe a few weeks until they die.”
Kelly: “Again!”
A natural and ultimately universal process, death is our greatest mystery. The zombie apocalypse may not be coming anytime soon, but it has been fascinating learning about the biology of death. Science can aid our understanding of the concept of zombies, but more importantly teach us about our own biological demise. Thanks to Meg’s husband for chatting with us. He may be too afraid to watch horror movies, but he sure does know a lot about death!
It might be terrifying to think of our loved ones biting into our flesh, although unlike their monster counterparts, zombies are not malicious. George Romero describes this fundamental difference, “you can’t really get angry at them, they have no hidden agendas, they are what they are.”3 Perhaps there is something comforting about the prospect of coming back from the dead? If only to stumble mindlessly in search of a delicious, screaming meal.