Last November, the first half of season three of The Walking Dead ended. And then afterwards, a strange story started doing the rounds. The short version goes something like this: after the Season 3 fall finale, a 26-year old Long Island man started arguing with his 22-year old girlfriend over whether or not a “zombie apocalypse” could happen in real life. She said “No” and he said “Yes” and somewhere along the way he shot her in the back with a shotgun. (This is the NY Daily News’ version). This kind of story is sadly not new. The “zombie apocalypse” idea has been like a wildfire, raging uncontrolled for several years now. It gained steam following the success of movies like 28 Days Later and Dawn of the Dead as well as book as World War Z.
Heck, as I was writing this, Discovery Channel premiered a brand new special on the zombie apocalypse that was entitled…uh…”Zombie Apocalypse.” Unfortunately, rather than touching on the potential science of it – you know, grabbing some neuroscientists, biologists, virologists, epidemiologists and social scientists for interviews – they’ve turned it into another episode of Doomsday Preppers mixed with the kind of late-night fare (like Unsealed) that doesn’t really advance anything but people’s preconceived notions.
So I figured I ought to help people given that A) I like to and B) I did both stay at a Holiday Inn Express and study biology. Now obviously, this is just my approximate response to the question at hand. I’m sure that there are scientists with far better education and experience than I who could argue the points I’m going to make. All that said, in answer to the question “Could a zombie apocalypse really happen?” there are two possible answers.
The short answer: “NO!” The longer answer: “Not the way it’s displayed in movies.”
All zombie fiction – whether Romero’s classics or The Walking Dead – give approximately the same basic description of a zombie: a zombie is a deceased human being whose body has been reanimated. The body retains basic motor skills and functions but in a decaying state. Zombies lack higher brain capacities like memory or psychosocial engagements like love or friendship. The zombie is driven by an insatiable hunger for flesh – specifically, human flesh – and will consume anyone they encounter. The only way to stop a zombie is to destroy the brain. So let’s start here. (I’ll touch on the modern take on zombies in just a moment).
Why can’t a zombie apocalypse happen? Because of the human brain.
Your brain is an amazing organ – even when you use it for nothing more than watching junk TV. Three pounds of grey mater with the consistency of tofu, it nonetheless controls every aspect and moment of a person’s life. It never shuts down. Even in sleep, the brain is processing information and doing repairs to the neuron pathways throughout its cortex. It controls both the voluntary and the involuntary aspects of your body’s functioning – try to think about your heart beating or focus on your breathing or see how long you can stop your eyes from blinking.
To do all of these functions, the brain is a hog for energy. Between one-fifth and one-fourth of your daily energy intake will be sucked up by the brain. The body takes in, on average, about 2400 kilocalories every day and the brain will take somewhere around 480 of those kilocalories. It also takes one-fifth of your daily oxygen intake. The primary source of energy for the brain? Glucose, the six-carbon molecule that is the result of breaking down complex carbohydrates such as starches, grains and processed sugars.
Here’s the kicker: the brain lacks the space to store glucose. With every nook and cranny inside the head taken up with cerebrum, there is nowhere for the brain to hold even just a small amount of glucose in case there is a delay in delivery. It relies on a continuous stream of glucose via the bloodstream to power itself. A delay of just four minutes leads to permanent brain damage – where parts of the brain, deprived of glucose to power themselves, shut down. Extend that to six minutes and you reach the point where brain death occurs. Past the point of brain death, you cannot fire that engine back up.
So let’s say a human being, bitten by a zombie-virus-infected monkey dies. That is, brain death has occurred. That human is not getting back up again. Even if the virus were to somehow jumpstart the brain, by definition, the rest of the body is dead – and the rest of the body includes the heart. So where is the brain getting its energy to send signals to limbs so that they can move? How is the brain receiving and recognizing the sounds of footsteps, car horns and other telltale signs that human prey is nearby? And how can a zombie send signals to the arms to reach out for a victim to gnaw on?
Even if you believe that the zombie virus could somehow kick start the brain, fire up neurons and manage to reconnect all the dead neurological power lines, you run into a second problem: glucose. As I said, glucose is derived from starches, grains, fruits and other carbs-heavy nutrients. You know what’s low on carbs? Human flesh. Since we’ve yet to see a zombie mix in a fruit salad in any movie/show/book, let’s assume that they’re not consuming carbs at all. So how is the brain continuing to work?
In short, the physiology and energy demands of the human brain make it A) reliant on specific sorts of nutrients for its primary source of power which B) isn’t provided in the “All-Human” zombie diet which C) makes it impossible for the brain to be turned back on after it has stopped receiving nutrients. So, no zombie and no zombie apocalypse.
Now there were some studies in the 1920s about all-meat diets, particularly as it pertained to Eskimos. However, that study allowed for consumption of a variety of meats – beef, lamb, fish. Zombies, for the most part, are after just one type of meat. And that study made it clear that, in order to prevent ketosis (elevated levels of ketones in the body, which occurs when glycogen stores in liver are used up) consumption of fat was a necessity. After a few weeks of zombie apocalypse, most of the “fatties” would be gone. Remember Zombieland?
Also don’t forget that the incubation period for viruses – that is, the period it takes for the virus to enter your system and make its effects known – is often a matter of days. Even a virus like influenza takes anywhere from 1 to 3 days to incubate. So, the idea of a fact-acting virus, as often depicted in zombie movies, is wrong. They show it being fast-acting because no one wants to sit through days when only a single zombie pops up and can be immediately terminated or quarantined. You need a horde of zombies to make a zombie movie work.
But you’re probably saying “what of the modern, 28 Days Later zombies?” The ones who are not deceased humans reanimated but simply virus-infected humans who’ve gone on a tear through civilized society? Well, obviously, if they’re not the “walking dead” then they can be handled in just a similar fashion as you would any other pandemic. And, to put it bluntly, the fact that they’re not “zombies” means you can pretty much shoot them wherever and they’ll go down – no need for a headshot. Even if you decide to not get into shootouts with infected humans, the rest of the pantheon of ailments, bacteria, viruses and conditions that affect us would affect them just as well – with one key difference. They aren’t actively seeking medical care. Bone breaks, tissue damage, injuries to the neck, spine, muscles and rest of the body would affect them just as well as they do us. They just wouldn’t be seeking medical care or getting a doctor to come near them.
So you can stop worrying and relax. There is no zombie apocalypse coming. We aren’t going to turn into mindless monsters who gorge on the flesh of friends and neighbors after one bite. Even if there is a zombie virus out there, it’s ability to destroy human civilization is limited. It would be the biological equivalent of a small forest fire – burning hot and fast, but burning itself out. We are more likely to be under-threat by idiots hoping for a zombie apocalypse than we will ever be from any real-life zombies.
Now the robot apocalypse? That scares me!