By Alex Goldberg P.H.D.
Zombies are THE most popular movie monsters in history. Since Night of the Living Dead came out in the 60s, way too many movies have focused on hoards of the undead taking over the world and mindlessly eating anything with a pulse (my personal favourite of the last few years was Zombeavers, a film where—you guessed it—deadly zombie beavers terrorise some kids in the woods). It even spawned The Zombie Survival Guide, a national bestseller, with some believing that there could eventually be a zombie apocalypse in the near future. Well, I’m here to tell you that’s hogwash and you all should be ashamed of yourselves. What gives me the right to shame you like that? I know enough about basic biology to tell you why there could never be such a thing as a bloodthirsty, undead mammals. Remember, undead is key here, as there are plenty of bloodthirsty mammals in this world (lawyers, for instance).
So, where to start? The most noticeable thing about the undead is that they don’t breathe or circulate blood, yet some of them seem to move even faster than healthy people. These two things run counter to each other in obvious ways: we need oxygen to breathe and we need to remove carbon dioxide in order to remain alive. These two molecules circulate through our blood and our lungs, taking in oxygen and removing carbon dioxide. In zombies, none of that occurs, so oxygen never gets to the cells and carbon dioxide is never removed. In normal humans, lack of oxygen can affect the body in many ways, but the worst way is by killing your brain cells, the same ones that coordinate thought and movement.
Why does the lack of oxygen kill brain cells in the first place? Well, oxygen is used for a very specific function in the cells: its main purpose is to donate electrons to the electron transport chain, which generates something called adenosine triphosphate (ATP). ATP is the primary molecule used for energy in every cell of your body. So, no oxygen means very little ATP generation. There are ways, such as glycolysis, which make ATP but don’t require oxygen, but your brain can’t subsist on glycolysis for long. It needs oxygen and, if it doesn’t get it within minutes, cells start to die. But they don’t just slowly whither away because they don’t have enough energy to perform their basic tasks. Some of these cells actively kill themselves via something called apoptosis—a coordinated cellular program that involves multiple factors signalling to the cell to cut it up into little pieces.
After all that, you’d be left with a zombie that’s pretty well braindead. I mean, it goes along with what they are, but how would you coordinate even basic movement without a brain? All functions run through nerves that link your muscles to your brain, which dictates movement. But suppose for the sake of argument that a poorly functioning brain could be induced via virus or something to stimulate enough nerves to move your body parts. Early on, those body parts would be way too stiff to move, and later, once they’re relaxed, you’d never generate any force to move them. Another funny side effect of having very little ATP is rigor mortis. In your muscles, there are proteins that work throughout your muscle fibres, called actin and myosin, that form something of a molecular lever. The actin-myosin complex generates force on its own, and it releases its stiff posture through ATP binding. So, ATP binding is actually needed to relax your muscles, and when there isn’t any, your muscles just seize up. Eventually, your proteins will just degrade without any ATP to make new ones through RNA and protein synthesis.
And there you have it. There will never be any undead human zombies in your or my lifetime (or ever). You can now frame that survival book and sell your intricately designed and well-stocked zombie shelter because you don’t need it. It was all in your imagination. Now, when it comes to LIVING flesh-eating human zombies, you may want to stay indoors.
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