How could a zombie actually work?

[Kalmageddon]

In the recent years zombies have been frequently portrayed in various media and I feel I've been overexposed to them, to the point where I started over analyzing them.

We all know the basics, a zombie is a reanimated corpse that is somehow impervious to every injury save for having their brains destroyed.
Except that this makes no sense. A human body is designed the way it is because it wouldn't work otherwise. We need to breathe, we need to have a heartbeat and blood pressure, otherwise everything shuts down.
Obviously.

Most zombies are justified in their media by vague explanations like a virus that reactivates the brain or something like that, but this still seems pretty vague and implausible and I basically just roll my eyes and force myself to go with it nowdays.

So here is my question for the Playground: what would it take, theoretically, to create a zombie in the way Hollywood protrays them? What kind of changes should happen to a body in order to function with only a brain and nervous system? How could something make a corpse go again without violating termodynamics and biology*?
Of course I'm not asking for anything practical or plausible, just for an explanation to the inner workings of a zombie that would pass a superficial analysis from someone knowledgeable in biology and other relevant fields of study.

Go wild!



*Not too badly at least... : P

[Tylorious]

There are parasites that lodge themselves into the brains of living things and change the way they act. Some have small changes such as a slowed reaction time, whereas others have drastic changes like causing a mouse to actively find and be eaten by a cat so the parasite can reproduce in the cat's stomach, only to be defecated and eaten by yet another mouse. These types of parasites may someday evolve to "pull the strings" of a human and cause them to do things they normally wouldn't. This may progress further to where the parasite is running the body even if the original host is dead. This parasite would want to reproduce as much as possible so it would leave offspring in the mouth of the host and cause it to spread the contagion to others. Once the entire population of hosts are infected, and there is no where else for the parasite to spread, they will eventually run out of food (brain) and die. The only thing this doesn't explain is why the human bodies eat flesh after it is infected: maybe its a reaction left over from the previously living human, the desire to eat. This is what makes the most sense to me.

[Spiryt]

They don't.

This is not right question, since it's right up there with 'how do dragons fly'.

For standard fantasy purposes, something like above ^ is perfectly sufficient.

[Haruki-kun]

Sort of agree with Tylorious, except for the host being already dead.

Truth is, the only way I can see a zombie happening is with the newer "infected"-type zombies, which is to say that the zombie is not actually dead: it just can't control itself. In order for the zombie to move, the muscles need to be working, and they obtain energy from food, and they need oxygen, and the excretory system needs to work for the waste to be disposed of... there are way too many things that just wouldn't happen if the body was dead.

Also, Neil DeGrasse Tyson explains it better.

[Zaggab]

The modern definition of dead is "When all the functions of the brain has been completely and irrevocably lost", which would mean that a corpse that reanimates already has a functionally destroyed brain, so for something to become a zombie that is killed by destroying the brain, some of the brain must still be functional, in which case the zombie-to-be wasn't dead in the first place.

As Tylorious wrote, a hypothetical parasite (or other pathogen) which hi-jacked the brain of a human, which also removed the response to pain as well as causing vasoconstriction (as some drugs do) would give rise to something with zombie-like behaviour which would appear to be unaffected by trauma to the body and limbs. Vasoconstriction would also give the appearence of corpse paleness.

To be able to move, the zombie would need some kind of circulation and metabolism, meaning that it would need oxygen, blood flow and food to survive. A human can survive about 3 months without food, so assuming the zombie would still be drinking, it could move about quite a while after zombiefication. If the hypothetical parasite also lowered body temperature, metabolism would slow, allowing the zombie to survive longer. This would also make the zombie slower, and would explain the shuffling gait and slow reactions of classic zombies. A lowered body temperature would simulate algor mortis (cold body after death).

As for spreading through bites, several pathogens spread through saliva such as many viruses (cold viruses, herpes viruses, rabies etc) and at least malaria (a parasite) spreads through the "saliva" of mosquitos.

These zombies would still be vulnerable to dehydration, and would eventually die from wounds to other body parts than the head, but more slowly than a human. Spinal and neural injuries would still paralyze it. They would still need to breath, but if the parasite upregulates oxygen-binding molecules in blood and other tissues, it could go without breathing longer, imitating no breathing at all for shorter periods of observation. So, not quite a "real" zombie, but similar, especially during a brief encounter with them (as when you're hacking them down with chainsaws or blasting them with shotguns)

[Ravens_cry]

Yeah, the parasite could work for creating the stumbling, groaning, moaning, and even violent tendencies. You can even give them a modicum of super strength because the brain's safety measures to stop one from hurting oneself can be turned off. However, then you run into the problem such creatures are still living creatures. They still need to eat and drink, so after a few days, at most, they should be dropping from lack of water, not to mention hypo- or hyperthermia depending on the weather.
Also, stumbling into someone and biting them is not the most efficient means to spread disease, so, unless this is being intentionally spread, it's not going to last long. Heck, even then, there isn't going to be much spread beyond the initial generation, which defeats the purposes of a biological agent.
So, while disease, parasite or even chemical 'zombies' could work short term, they don't have the staying power of zombies without some considerable extra stuff.

[Thunderfist12]

Zombies work like this.

[SiuiS]

There are none. To move a corpse would require something. Either the host would have to remain alive enough, and moist enough, that hydrostatic shock could kill the brain-thingy; but then body shots would eventually take it down. Or the brain would have to, I dunno, insert muscular tentacles throughout the body, to mechanically move the limbs and such, but then it's vulnerable to being attacked. Eventually, an animate body will wear away to nothing, through erosion if not decomposition. Without magic, a zombie cannot exist.

[factotum]

The most "realistic" portrayal of a zombie I read was in a Larry Niven short story. Basically, it was an infection of sorts that re-animated them, but the first thing said infection had to do was restart the heart so it could access other areas of the body; the people who are being attacked by the zombies figure this out and defeat them by injecting them with a full-spectrum cure that kills every disease, including the one zombifying them.

The only thing that the story kind of glossed over was how the infection got into the corpse's heart in the first place...

[Ravens_cry]

Zombies work like this.

Yeah, I already mentioned the problems for that if you want a full bore zombie plague. Damn if that doesn't look freaky though, like elephant toothpaste exploding out of everywhere.

[zlefin]

Magic.

Really magic is the most plausible explanation.
It lets you get around all of the physics. So having the process start with some loon casting ancient magic spells from old dusty tomes lets you justify it all.


also, zombies are like the force, it's best not to try to explain how they work in detail.

[Amidus Drexel]

I think the real issue here is finding someone to hire a zombie in the first place, as there are a few jobs where the work could easily be done by a mindless worker as by a human.

On a more serious note, I like the voodoo idea of zombies, which is pretty much just "a wizard did it".

[the_druid_droid]

Just for the sake of discussion, I should point out that there are lots of anecdotal accounts of people under the effects of PCP behaving in a "zombie-like" way, i.e. excessive aggression, near-immunity to pain, and bizarre behavior.

Some sort of chemical or virus with similar but longer-lasting or irreversible effects might provide a good rationale for "fast zombies". Also, the conventional wisdom about aiming for the head could be a result of the fact that only a direct heart shot would bring down this type of zombie sufficiently rapidly (and there are big game hunting anecdotes that animals charged with adrenaline can keep rushing a hunter even with a ruptured heart, albeit briefly). Since the head is smaller than the torso, but still larger than the heart, especially for panicked survivors, that would make a more probable target and contribute to the myth that only headshots kill the creatures.

[Silver Swift]

Really magic is the most plausible explanation.
It lets you get around all of the physics. So having the process start with some loon casting ancient magic spells from old dusty tomes lets you justify it all.

I agree with this, in order to make zombies even moderately plausible you need either magic or nanotechnology that is so advanced it might as well be magic.

also, zombies are like the force, it's best not to try to explain how they work in detail.

See, that I don't agree with. Magic works best when it is explained, so lets give it a try:

The way zombies behave works best as some kind of magical scavenger or parasite, a creature that inhabits a dead humans body, takes over whatever it can use and slowly consumes the rest. The parasite enters the body as a microscopic larvae and travels the bloodstream until it reaches the brain. Once there, it starts to eat. In a matter of days (or hours, depending on how effective you want this plague to be) it grows to its full size, taking up the entire inside of the skull.

It then spreads tiny tentacles throughout the host body. These tentacles serve two purposes: they consume the parts of the body that the parasite no longer needs, sending the nutrients this generates back to the skull where they are used to keep the parasite alive and provide the required energy for the second task, reactivating and upgrading the body's muscle tissue. At the same time the parasites eats its way through the eyes and replaces them with its own sensory organs (whatever they are).

Once the host body is functional again the parasite lays eggs in its mouth and starts to wander about, looking for still living animals in which to lay its eggs and start the cycle again. After the parasite has eaten it's way through the entire host body the parasite dies, though this could take quite a while because the parasite only uses the exact parts of the body it needs, rather than having to constantly keep everything active and healthy like humans do (alternatively you could have the parasite feed on livestock and other animals, only spreading itself to other humans to make it last longer. Though this will likely not extend your apocalypse by much).

Advantages of this approach:

• Zombies are super strong dead humans that can survive having large parts of their body destroyed and can be killed without moral qualms.
• The zombie plague spreads by bite.
• If you destroy a zombie's "brain" (actually the parasites true body) it dies.
• Burning the zombie (or infected person) deprives the parasite of it's nutrients so it dies faster.

Disadvantages:

• Like with most zombies in fiction there is no way this creature can plausibly infect a large part of the human race or present a credible threat to any significant group of survivors.
• The parasite dies after a fixed amount of time, so a sustained apocalypse is unlikely.

[Emmerask]

In nature there are quite a few parasites/viruses which create "zombie" (the virus version) like behaviour best known would be certain rabies strains I guess.
(Though I do not know if humans actually become more aggressive?).

So some form of super rabies which creates extreme aggressiveness in humans would be the best guess for a working zombie?

The undead version ...well as others have said magic seems the only explanation which could work

[erikun]

Well, assuming you don't want the magic approach, which would be like voodoo zombies or a nth-dimensional spacetime energy virus...

In order for something to stand upright and bipedial, you'll need to have the muscular system active. In order to remain that way, the nervous system will need to be active, and probably a small portion of the brain for stuff like equilibrium. Senses will require more parts of the brain active, although sound and smell would likely require the least, meaning potentally no higher-brain functions.

Of course, the biggest problem is getting sugar/oxygen to those systems. Keeping the cardiovascular system running, complete with breathing and a beating heart, would do it - although at that point, we're more talking about some parasite controlling the body. I suppose it might technically be possible for some bacteria to dissolve "unnecessary" parts of the body (like fat and skin) to produce the required energy, although I wouldn't expect it to be an efficient (or really even practical) method.

The bacteria idea would potentially give you a body that can move around on its own, smell and hear, and stay mobile for a few weeks before falling apart. It isn't likely to run up and bite anything, but then again, being a walking plaguebearer makes that somewhat unnecessary. The only purpose for this thing would be to move to another location before falling apart and allowing the bacteria to spread.

[WarKitty]

A significant part of the problem is that humans just aren't built for biting as an aggressive action. Human teeth aren't designed to easily pierce skin, and the human skull isn't designed to put teeth forward in a way that would be conducive to biting.

That goes double if you want them to eat brains specifically. The human skull isn't easy to open.

[thubby]

28 days later isn't wholely unreasonable. the modern take on zombies is based on rabies already. the idea that it could get more virulent isn't even that crazy.

the human body is capable of functioning remarkably well even after taking critical damage. just look at the crazy stuff people do on drugs. there's very little that mechanically prevents a human from accomplishing what we see zombies get away with, it's our own body's attempts to keep us safe and alive that impose the greatest limit.

[Ravens_cry]

28 days later isn't wholely unreasonable. the modern take on zombies is based on rabies already. the idea that it could get more virulent isn't even that crazy.

The trouble the zombies is the living 'zombies' would die off, or at least be incapacitated by sheer dehydration very quickly. A couple days at most. If you have an outbreak, quarantine the area, encourage or force everyone in the area to stay inside, and it should die off on its own accord.

[thubby]

The trouble the zombies is the living 'zombies' would die off, or at least be incapacitated by sheer dehydration very quickly. A couple days at most. If you have an outbreak, quarantine the area, encourage or force everyone in the area to stay inside, and it should die off on its own accord.

which is precisely what happens, granted its over the course of a week or so but im willing to give hollywood that much license.

actually, depending on what the virus does, it could improve response to dehydration by reducing liver and kidney functions, among other things. a week or 2 of highly contagious, body fluid leaking fury would be enough to be a world health crisis at least.

[SiuiS]

The trouble the zombies is the living 'zombies' would die off, or at least be incapacitated by sheer dehydration very quickly. A couple days at most. If you have an outbreak, quarantine the area, encourage or force everyone in the area to stay inside, and it should die off on its own accord.

Oh, no fair! You changed avatars, too!


DD, while PCP might induce similar symptoms, you're looking at burning out the body incredibly fast. Over adrenalation (is that even a word? Is now~!) impairs fine motor function and can cause the heart to burst. And I mean impair fine motor function like 'cannot remain standing upright'.
If a zombie consists of
-murderous
-impervious
-implacable
-long lasting

The. You're not going to get a zombie by any biological process. Not a human one. You'll have accounts where people will refer to it as a zombie, but 1 & 4 counteract each other, and 2 & 3 are remarkably unlikely when 4 is also necessary.

I suppose in theory a series of parasites which all communicate with each other through the interstitial fascial network of the body and work like a unit a-la jelly fish could have specialized "king" worms that work into the head and receive basic information from the spine, and transmits data along "courier" worms that are fast and responsive and in turn spur "thrall" worms that contract muscle mechanically, but then we have the problem of this being a very, very energy intensive system. You'd need an additional gut worm to, like, process all the intake and then distribute it to the entire rest of the body, which... Is functionally like super rabies, except the head will still move for a while after removal.

I guess PCP rabies with zombies only dying of their wounds 'off screen' is the best we'll get.

[Brother Oni]

actually, depending on what the virus does, it could improve response to dehydration by reducing liver and kidney functions, among other things. a week or 2 of highly contagious, body fluid leaking fury would be enough to be a world health crisis at least.

Except you'd also have to disable or impair homeostasis functions to reduce water loss and messing around with thermoregulation to stop water being lost by sweat is going to cause the death of the zombie in very short order.

The core temperature only needs to hit 40C for it to become life threatening and with all that massive physical exertion, most zombies would die off in a few hours (deaths from MDMA overdoses are typically through hyperthermia and such deaths usually occur in nightclubs, thus a similar conditions of physical activities), or quicker if the environment is hotter.

[Eldan]

So. There's actually two different questions in here, the way I see it.

The first is: how would a single zombie work? That the easy part, really. Drugs, viruses, both can work. At least so far as to turn a human stupid, aggressive and near immune to pain.

The second is a spreading zombie plague. I don't really believe that one, for reasons of epidemiology. Or ecology, if you want to call it that. What is the zombie's food source? Humans. What is the zombie's means of reproduction? Also humans. What is the zombie's main predator? Why, more humans.

This really can't work.

[factotum]

Except you'd also have to disable or impair homeostasis functions to reduce water loss and messing around with thermoregulation to stop water being lost by sweat is going to cause the death of the zombie in very short order.

I should maybe have added to my zombie explanation earlier: the zombies in question only survive for one night, so long-term issues with thermoregulation and whatever aren't an issue...

[Brother Oni]

The second is a spreading zombie plague. I don't really believe that one, for reasons of epidemiology. Or ecology, if you want to call it that. What is the zombie's food source? Humans. What is the zombie's means of reproduction? Also humans. What is the zombie's main predator? Why, more humans.

This really can't work.

It works if you view the zombie as a host for the parasitic organism inside (dependent on type of zombie).

The food source aspect is just a byproduct of the organism trying to keep its host alive long enough so it can spread. There are a number of such organisms which cause its host to be eaten by predators so the parasite can continue its life cycle inside the predator.

Being eaten intentionally sounds more ludicrous on the surface if you don't distinguish between host and parasite.

[Eldan]

Still. Every human eaten is one that can't be turned into another zombie. That just doesn't work out.

So, to work, the zombies would have to bite other humans, then let them go and mainly eat other things. Which makes them quite a bit less scary.

[Tylorious]

Still. Every human eaten is one that can't be turned into another zombie. That just doesn't work out.

So, to work, the zombies would have to bite other humans, then let them go and mainly eat other things. Which makes them quite a bit less scary.

You might think that, but if you think about World War Z, where it's kind of just a disease and they run stupid fast, it becomes scary again.

[Ravens_cry]

which is precisely what happens, granted its over the course of a week or so but im willing to give hollywood that much license.

For the sake of a move, perhaps, but not for the sake of an actual thought experiment/discussion.

actually, depending on what the virus does, it could improve response to dehydration by reducing liver and kidney functions, among other things. a week or 2 of highly contagious, body fluid leaking fury would be enough to be a world health crisis at least.

The liver and kidney do some very awesome things. Those toxins build up pretty fast. Liver and kidney failure would kill the disease zed pretty fast too, even if the disease could prevent a need for water. And , of course, hyperthermia, which changes to prevent water loss would just make worse, is still a concern as no water loss means no sweating. Not to mention hypothermia. It takes a lot less than one might think, especially if wet, to become hypothermic to the point of impairment.

[Emmerask]

OR these rabies zombies just drink some water when they become thirsty

I know its not perfectly zombie like but I would say reasonable

[Karoht]

Look up the webcomic "under the dead skies" as they detail their zombies as being based on a real world fungus called Cordyceps.
http://en.wikipedia.org/wiki/Cordyceps

For reference, this comic was out for a year before that zombie game The Last of Us used it.

Either way, good places to start researching.
Cheers.