Delay the Decay: How Zombie Biology Would Work

By Kyle Munkittrick | October 29, 2010 5:23 pm

Ma'am, please, the sign clearly says "Keep Off the Grass"

Halloween is a-comin’ and this Sunday brings us AMC’s The Walking Dead. In honor of that, we’re discussing The Ethics of the Undead here at Science, Not Fiction. This is part II of IV. (Check out parts I, & III)

Before we can start investigating whether or not something that craves brains has a mind or should be pitied, we need to define just what, exactly, we’re talking about when we talk about zombies.

I’m going to start by ruling out the 28 Days Later zombies and the voodoo/demonic zombies of Evil Dead. First, the name of this blog is Science, not Fiction, which means any religious hokum is right out the door. Demon possession, souls back from Hell, and voodoo are not going to be considered in this investigation. On the other end of the spectrum, in 28 Days Later anything infected with “Rage” becomes a “fast” zombie. In essence, Rage is rabies only way, way scarier. Thus we aren’t dealing with the “undead” so much as the violently insane. So non-fatal pathogens don’t count either. If the pathogen doesn’t first kill you, then re-animate you, then you aren’t a zombie.

Which leads us to the next question: how does the pathogen work? I am not denying here the multitude of variations and nuances among zombie plague viruses, so we have to come up with a generic, realistic version to have our discussion. Zombies generally meet three important criteria. They are 1) stimulus-response creatures that seek flesh 2) continually decomposing and 3) contagious via bodily fluids. If we can explain, reasonably, how and for what reason a pathogen might cause/allow these conditions, we can describe a realistic zombie pathogen.

Condition 1, that zombies are stimulus-response creatures that seek flesh, implies that the pathogen must act to re-animate the existing neural pathways and motor functions in some fashion. Let us presume human-only infection and that the virus, being species specific, results in a cannibalism preference. Thus the sensory systems which are re-activated are capable of distinguishing four key things: flesh-vs-not-flesh; species; infected-vs-uninfected; self. Furthermore, for the sake of simplicity, the virus does not create any new systems, it merely hijacks existing ones.

Next, we have to remember that contracting the zombie pathogen is terminal. Whatever the hijacking process involves, we must presume that an intermediate stage of infection between contamination and zombification is fatal. If I had to guess, the infection of the medulla oblogata – where most automatic processes are regulated – is what results in cardio-pulmonary death, followed shortly by brain-death. Sometime after brain-death the medulla is fully hijacked by the zombie pathogen, jump-started (I won’t attempt an explanation) and re-animation is underway.

Whether it is musculature, perceptive organs, or circulatory and digestive systems, the virus must work with what it has. The metabolic process continues, arguably for both the body and the pathogen, which in large part informs the indiscriminate hunger for flesh. It is critical here to note that a zombie body is not uniquely strong (in fact, the opposite), nor can the body function properly without oxygen, waste disposal, and nutrients. We can, however, presume that a zombie body can, in its own way, marginally function when some of these requirements are missing. However, when an eyeball is gone or the intestines finally rupture, that zombie has lost whatever sense or function was associated with the now deteriorated organ: no healing happens.

Which leads us to Condition 2, that zombies are continually decomposing. No one thinks of a zombie as a healthy, mindless body; you think of a corpse that moves. The re-animation process is, we assume, imperfect or it would be revivification. One of the imperfections is that autolysis – the process wherein a cell’s own enzymes begin to consume it – is not stopped or reversed. As autolysis is the first step in postmortem decay, even a brief period between death and re-animation would cause it to start. Other aspects of decomposition, such as purification and insect infestation, though significantly slowed would likely continue as well.

Based on the average zombie, we can presume a few things about the virus’ relationship to decomposition. First, is that the zombie virus slows decomposition by providing cells with some nutrients. Second, is that the immune system, at least a crippled version, still functions to slow human bacterial flora from consuming their host. Third, it could be presumed that while some cell division continues, repairs and restoration are lost. Fourth, the virus would likely only preserve essential functions, allowing irrelevant parts of the body, such as skin, secondary musculature, and some organs to decay. Finally, we can presume the virus itself must consume flesh to some degree, rendering the zombie’s metabolic processes incredibly inefficient and explaining the insatiability of a zombie. Thus, a zombie frozen in the arctic would likely re-animate upon thaw (pathogen in stasis; corpse preserved) while a zombie at the bottom of the ocean would first suffocate (albeit more slowly) and then be crushed.

Condition 3, that the pathogen is contagious via bodily fluids only, is a critical detail in terms of both staying true to the mythology of zombies and for presenting a scenario in which not everyone would instantly be zombified. An airborne pathogen, particularly one with any sort of incubation period, would be total, unstoppable pandemic. But, more importantly, we are dealing with a creature of fiction. And, just as with other members of the undead (e.g. vampires, werewolves) the bite gets in the blood and turns you

Remember, we almost never see someone getting bitten by a zombie and then not dying and “coming back.” The reason is that a bite both by-passes traditional levels of the immune system and delivers a huge dose of the pathogen directly into the circulatory system. Furthermore, it immediately contaminates the flesh directly exposed. As the zombie pathogen, whatever it is, seems able to interact with most cell types, not just specific ones (as with HIV), it would make sense that direct exposure would allow the virus both permeate the whole system (body) while beginning total infection at the site of contamination as well. It only takes one bite!

There you have it. A zombie pathogen must 1) be transmitted via bodily-fluids to 2) ensure sufficient and total infection which 3) is always fatal due to the fact that pathogen must 4) either consume the host or host-acquired flesh 5) hijack all the necessary functions for movement and sensation 6) provide at least some nutrients to itself and the body 7) allow continued movement and 8.) slow the decomposition of the host body.

Promotional Image via by Scott Garfield


Comments (19)

  1. dave chamberlin

    Guys like gross zombies, while women theses days are apparently infatuated with vampires. Put some fun psuedo science into the reasons for that.

  2. GregW

    What kind of real-life examples exist to illustrate the “hijack” and “jump-start” processes? In my non-scientist experience, C. unilateralis (the oft-cited fungus that causes ants to sacrifice their lives to spread spores) seems like a suitable example.

    How much of the brain, and what level of complexity, must be preserved to enable zombie behavior? If the pathogen must provide nutrient secretions, a pre-existing fungal infection also seems to fit the bill.

    Lastly, should we assume that zombies actually process the flesh they eat and gain sustenance from it? Day of the Dead, the third film in Romero’s classic series, establishes that the zombies are compelled (programmed?) to eat flesh, but don’t derive any nutrition or benefit from it. In the case of a pathogen (in Night of the Living Dead, the cause of the zombie outbreak is presumed to be unusual radiation brought to earth by a space probe), the cannibal behavior can be explained as a reproductive strategy: exploiting the existing bodies of humans and their instinctual urges to eat.

  3. Idlewilde

    To Dave- I’m a girl and I like zombies….way better than sparkly ass hairgelled jerks who are lame enough to wear *beige* leather jackets…seriously, edward should save that for the has-been stud at the senior home….anyway, this was a great article. It’s fun when fantasy stuff is scientifically analized.

    One question: If a guy who was bitten by a zombie got his bitten arm amputated directly afterward, would the virus not have had time to spread? Would he survive, all risks of amputation aside?

  4. @GregW: Thanks for the example! I was thinking that, but didn’t want to add any of the real-life examples (the article was already getting a bit long!). As for exact brain regions, no idea, but the medulla and pons seem critical, as well as rudimentary visual/sensory processing regions. On your last point, that is just a great question – I presumed that a virus + body’s natural burn rate would require double the nutrients, plus I wanted to explain why zombies lusting for flesh would benefit the virus (evo bio explanation, I guess).

    @Idlewilde: That’ll teach Dave to generalize. My guess, with your question about amputation, is that a person would only have a few minutes to amputate if bitten in an extremity. This is all made up, but with some venom (like black widow) the poison does far more damage in the heart than in the extremities. I guess it would depend on blood flow up the arm and point of entry. But, yes, if you amputated in time the person would be ok.

  5. OtherGregW

    I’ve considered this and believe zombification not to be based on viruses, but instead on hive-mind creatures of some sort, capable of reanimating (real, very dead) corpses to further their DNA-driven spread.

  6. Well, I picked a mutated (by alien microbes) mold strain rather than a virus for my book; I didn’t follow your rules, because I wasn’t looking for the same outcome. Despite the holes in the logic, I’ll put it forth for discussion:

    1) The mold “needs” (hand wave) neural tissue, which leads to the impulse zombies have to eat brains. Anything with neural tissue gets targeted.

    There are different strains; each strain “prefers” non-infected flesh but will also try to take over flesh infected by a different strain.

    The body stops “living” as a human and becomes a mold host; the mold takes over life functions.

    2) There are two phases of the main strains: mobile and spore. The mobile (zombie) form lasts only so long (hand wave) and then becomes a puff ball of spores.

    The mobile zombies can use mold to reattach body parts, although it isn’t pretty or structurally strong.

    The other strains have a third phase related to the alien genetics; I won’t say anything further about it here.

    3) Mobile zombies spread contagion via contact and fluid; spores are spores and thus even nastier.

    I wanted to achieve three things:

    1) A world in which people had to compete with another life form, a massive change.

    2) A world in which the most powerful weapons were bleach and alcohol.

    2) Brains that taste better than truffles. (It’s a comedy.)

  7. Sean Dunn

    How about a bacterium that spreads through bites. It induces production of hydrogen sulfide in the bloodstream, giving the illusion that the host is dead. The second phase is reduction in hydrogen sulphide and swelling of the host’s cells, with selective protection of the medulla and pons. The ensuing encephalitis would cause a rabies-like flailing and irrationality, and eventual cell death. The bacteria would survive from the digested materials from autolysis. In addition, a heightened olfactory sensitivity to stress hormones, and a surge in ghrelin hormone, which causes insatiable hunger.

  8. I would imagine that NO body functions or organs can really be done without, even skin,even by a “dead” entity. A virus depending on the survival of the host would actually need things like skin and a functioning digestive system, or the host would not function long enough to infect others, nor could it develop the energy to walk around hunting victims without a fucntioning digestive system, fully functioning lymphatic and circulatory systems, endochronological systems, electrolytic systems etc. No blood circulation means no oxygen and sugars for the muscular cells involved in motion. In movies, Zombies often have injuries of a catastrophic nature..the hero smashes one with a car, or hacks off an arm..or shoots it in the chest, and the zombie keeps on coming. Even a zombie with an injury like that would lose too much blood and oxygen. A broken back would make it impossible even for a zombie brain to get the legs to move or the heart to beat. A bullet in the chest would deflate the lungs and in minutes prevent the muscles from moving to to asphyxia. Long story short, if the virus reanimates the host, it had better reanimate EVERYTHING unless it wants a life span of no more than a few hours.

    If the process of decomposition has already begun, the zombie does not have much time before the host body becomes unreliable. Evolution simply would never give such a risky system good odds.

    Zombie flicks always focus on the persons fighting the hordes, but never on the zombies themselves. What happens to the zombies that don’t find anyone to infect..or even if they do, what happens to them over the long haul? I think they themselves would re-die in a matter of days as the functions fail so much that even the virus cannot sustain it.

    However, viruses usually never infect someone “for keeps”..they infect to use the host to reproduce, and their offspring go on to infect others and so forth keeping the species of virus alive but sacrificing the infecting viruses in the process. I think zombies hunt humans not to get sustinance, but to simply spread the virus.

  9. We should all find zombies depressing politically! Zombie flicks surge when Republicans are gaining control and fear the masses. Vampire flicks represent fear of a predatious-controlling aristocracy and surge when democrats gain. S’truth! In fact…

    There’s a whole monster CLASS SYSTEM. Vampires are old-style aristocrats (and worshiping them makes their fans true traitors), while zombies are the proletariat. So who’s the MIDDLE CLASS?

    Well, it used to be lycanthropes, werewolves. Poor schlumps in the suburbs, the only monsters with families,mortgages to pay and lawns that need mowing. Their affliction is portrayed with sympathy and angst and made for INTERESTING stories! Their new powers and temptations conflicting with bourgeois values, leading to inevitable tragedy…

    …except in the wonderfully up-beat and American TEEN WOLF.

    and except for the recent UTTER BETRAYAL of the whole idea behind wolfmen, in these awful new series that portray “lycans” as just another kind of arrogant asshole monster race preying on normal people, completely missing the point of what they are about!

    David Brin… author of The Postman and Earth

  10. AaronPM

    The classic Romero z0mbie’s are not infectious, its just every one who dies turns into a zombie. Being killed by a zombie only brings death and turning into a zombie faster than natural death.
    The fungal zombie works very well as it will spread out and make its own network that transports nutrients and motor control signals. The fungus will consume the body but lucky for the fungus we have huge reserves of energy in our bodies. The fungal zombie was introduced 30 odd years ago in a now classic AD&D adventure.
    Now when the zombies rise the Vampires will have to save humanity from extintion.
    IMO undead zombies are going to be slow not fast. Running is hard to do with the smallest metal impediment, Zombies are brain dead “no running”. The” Infected Living” zombies will be able to run but not very well.

  11. Hmmmm…. Interesting point David. So I pose to you the following question: what does it mean that zombies AND vampires have been surging in popularity spanning the Bush and Obama presidencies? Twilight took off in 2005, True Blood in 2008, with Zombieland in 2009 and The Walking Dead in 2010. Your trend is reversing, or rendering the political leadership irrelevant.

  12. Troy McCurrin

    @Kyle Munkittrick: Actually, in 2005, the Democrats were surging in popularity again, and retook the house and Senate in 2006. Now the Republicans are surging. I hadn’t ever thought about it, but David may have a valid point.

  13. @Troy McCurrin: even MORE interesting! Presidency vs Congress as a determining factor in which monsters we love. Who get’s sharktopus? The Green Party?

  14. Freshmeat

    There are many interesting points in this thread concerning the scientific plausibility of the ”Z” phenomenon. First the fast ”living” zombie is quite possible if you look at the various kind of micro-organisms that control their hosts : Fungi in the case stated above but also parasites that cause ants to go up to the top of grass blades to be eaten by cows and other examples. Lets assume that parasitic mind control does exist. If a parasite or virus infects someone and makes him more aggressisve, it could theoretically alter others functions such as pain perception and reaction to trauma as well as self-preservation instinct like toxoplasma gondii witch causes the mice to be attracted by cats. A super-aggressive human that feels no pain and cannot be put in a state of shock by heavy trauma is quite scary. In fact, if a parasite had to pass from one host to another to reproduce and the infection was destructive to the host, it is very likely that these neural functions, witch could pose an obstacle to the transmission, would be terminated. It would explain why the zombies are so tough: the human body is quite resilient maybe you pop a few rounds in the chest but miss the heart by a little, with no self-preservation mechanism it would just keep going at you and ty to bite with all its strength for the few minutes it has to live. I think that covers it for the ”living zombie”.

    For the ”dead zombie”, I think the most plausible scenario has already been stated above: a form of hive-mind unicellular creatures. Such a creature could simply use the already present structures of the human body but alter their functioning. Imagine that those creatures could produce energy from eaten flesh by themselves and distribute it throughout the body through some kind of ”osmosis”, that would eliminate the need for a pulse and respiration. The non-necessary organs would rot and the host would be dead but there would be a new life form inhabiting the body, maintaining the shape and the functions that serve the hive.

    Considering all those factors in favor of a possible zombie apocalypse, I would suggest you start packing food, water and ammo if you know what’s best for you and your family.

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