Self-organizing Criticality is much preferable to Evil Hive Mind
Zombie hording behavior is crucial to decision-making after the zombiepocalypse. Assuming that our rotting foes are dumb beasts with no mind at all may be our downfall, but all the classic texts seem to contain two fundamental assumptions:
- Zombies have absolutely no sentience or intellect
- Zombies gather together in hordes
Some texts also assume that zombies retain a very very rudimentary and instinctive memory of their activities as humans (crowding to shopping centres, walking along roads, etc.) but this could be a mistaken conclusion based on their hording behavior. How zombies form hordes is a key part of the zombiepocalypse puzzle: consider the ending of The Walking Dead[1] season 2, where zombies see a helicopter, follow it, and when they lose sight of it just keep walking in a straight line. This is very specific hording behavior, not necessarily matched to any existing understanding of self-organizing behavior. Understanding what happens in these kinds of situations is essential to planning anti-zombie defenses.
In most of my posts about zombie survival spots here I’ve worked on the assumption that zombies are mindless moving objects, kind of like the famous physicists’ perfect point particle. They move slowly away from their point of origin in a random direction, so if one moves away from a city one can imagine the wave of zombies emerging from the city just like a supernova, in a perfect sphere disrupted only by objects. I’ve also assumed that they follow the path of least resistance, so move along roads and open areas in preference to built up areas and forests. This means that a well-designed fence or hiding in a large complex of well-sealed buildings will tend to direct zombies away from a small group of survivors, and once the main wave of initial infecteds has spread outward, survival will become considerably easier.
However, this doesn’t seem to be how hordes function in the seminal texts. They seem to stay together and move purposively. This means, I think, that they have some kind of hording technique – some sort of self-organizing criticality, like insects. I think that their moans of bestial hunger serve the same purpose as an ant’s scent – when a zombie hears a moan, it moves towards the sound and itself moans, drawing other zombies. In The Walking Dead they also comprehend the difference between zombie and human scent, so maybe they remain close together due to some kind of scent marking process. The nature of this behavior is crucial, because if we assume that zombies horde together through a signaling mechanism and move along the path of least resistance, our tactics change:
- Staying hidden is essential when even single zombies appear, since the sound of their bestial rage may bring others
- Staying away from major roads is a good survival tactic
- As roads spread out away from cities, remaining out of sight in an area far from major roads will enable survivors to escape the worst hording behavior
- Major cities and megacities (like Tokyo, Chongqing) will have hordes of zombies potentially in the hundreds of thousands in size. If zombies have any kind of hording behavior, getting out of cities before the worst of the epidemic hits is essential. Once a significant number of zombies has been created, attempting to escape a city will be close to impossible, since being seen by even a single zombie will likely draw others very quickly
- If zombies can horde, tactics need to be developed to enable escape from a situation where a zombie sees the group before the group sees it. This makes choice of bases and camps much harder, and makes subterfuge much more important than weapon use
I think it is reasonable to assume that zombies adopt insect-like scent-marking and hording patterns, and to find ways to fool or avoid them. The best use of this behavior is in setting up traps from which large numbers of zombies can be easily culled, or establishing distractions which enable survivor groups to flee. Understanding zombie hording behavior is essential to identifying good survival patterns. Is it an insect-like self-organizing system, some kind of voodoo, vestigial human behavior that is easily fooled, or simple particle mechanics?
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fn1: which I consider to be the seminal text, much more knowledgeable than earlier efforts at Zombie science
picture taken without permission from Detrain C, Deneubourg J.Collective Decision-making and foraging patterns in ants and bees. Advances in Insect Physiology,35; 2008: 123-173.
Compromise and Conceit 
May 7, 2012 at 11:29 am
Zombie methods of prey detection is also a critical point to understand, probably even more so than hording mechanisms. I’ve always worked on the assumption that they’re drawn to noise and/or movement, but your assertion that scent plays a role is going to have critical implications to our defence strategies.
If we assume that the enemy does not randomly attack trees swaying in the breeze then at a minimum they are following:
1. Movement
2. Humanoid shape – potentially. This could be confirmed via animal testing
3. Sound
Now most of these are easily falsified, even without modern technology, to provide fertile trap setups.
If we assume that scent also plays a vital role then the defence strategies become even broader, as actions like carrying a rotting corpse or wearing too much Old Spice will potentially make a survivor invisible to the ravenous foes. [1]
The worst case scenario is that they are still operating on a human style multiple prioritised inputs, where movement, shape and sound are ignored if below a certain threshold without a scent confirmation. A factor to consider is that if the infected actually display the same level as intelligence as they possessed while alive we’re probably best off trying to get infected in a way that damages our looks to the smallest possible extent [2].
But we need to draw hope from the fact that all sources agree that the zombie menace can be survived, for a while at least [3], this means that we should not assume the foe is invincible. As long as we take sensible steps, such as not being a teenage girl who loses her virginity during the apocalypse, we can get through this together.
And if we can’t get through it together I can throw you to the horde and run.
[1] Bags not being the test subject to verify this.
[2] I’ve OK with being an intelligent walking corpse as long as 1) I can call myself a lich and 2) I’d prefer to still be as well preserved as possible. [4]
[3]And ultimately I only want to survive for a while, specifically the remainder of my life.
[4] Intelligent zombies would probably lead to all sorts of new markets in body repair and preservation – “Are you worried that your legs could give out allowing the prey to escape you? Try our new process to embalm you and we’ll also replace broken bones with new metal frames that’ll never rust for free! We can build you better, stronger, faster! After all, it’s not like there’s a danger you could die on the operating table!”
May 9, 2012 at 11:09 pm
Yeah, zombie prey detection is another mystery that really needs to be considered carefully. In most stories they seem to have weak prey detection and strong hording powers, except perhaps for 28 Days Later (where they have both). But in 28 Days Later they are also classic predators in a predator-prey model – they die out fast after their prey dries up. Weak prey detection and strong hording in undead means that one could potentially survive for months only to suddenly wake up to a million zombies on your doorstep. That’s some complex dynamics there, and I think it plays out in The Walking Dead a lot – complacency is a big part of the story, with the group going weeks without serious encounter and then coming up against a horde they weren’t expecting. I guess this is the most likely way in which pockets of survivors would hold out.
May 10, 2012 at 1:58 pm
28 Days Later is nonsensical though. Victims go into a frenzy and attack everyone around them manically – except other infected who they happily co-exist with.
What? If this was a virus that made you bite your neighbour once that’d make sense, but its described as the “Rage”, not as the “Flip out when you meet new people but then become relatively well behaved”.
Logically 28 Days Later infectees should radically thin their own herds (not a classic zombie problem) and have very weak hording behaviour (if any!). It’d still be a dangerous virus because even a single infectee is likely to infect a survivor, so the fact that only one person walks away from the fight isn’t an issue.
Though maybe I’m wrong. Maybe the logical behaviour for 28 Days Later is patient 0 is infected. He infects someone, they fight and and one walks way to infect more people while the other dies. That’d result in an average fight having only (say) 1.1 infectees walk away from it (maybe even less if they cripple each other once both infected). That’d probably mean the virus burns out in no time – the virulence of the violence and tiny period to take effect would actually prevent it’s spread…
May 10, 2012 at 5:09 pm
True, you’d have to suppose some effect of the virus on their target selection process, e.g. they can smell whether you have the virus, which would suggest an extremely strong target selection method (which to be fair they do seem to have).
If the average fight had 1.1 infectees walk away that would mean that the basic reproduction number of the virus was 1.1. That’s enough to maintain an epidemic (any reproduction number bigger than 1 will do the job) but would make the epidemic extremely slow growing and prone to collapse with even the smallest intervention (e.g. issuing body armour and clubs would probably shift the reproduction number below 1 and thus lead to epidemic extinction).
May 10, 2012 at 9:48 pm
I understand that a rate of 1.1 wouldn’t lead directly to the virus’s end. But it would drastically slow its rate of spread (down from the typical geometric zombie scenario). That would totally change the expected response from authorities. I mean you only have to send in 10 guards a couple of dozen times then watch one of them stagger away an infectee before the government line becomes “Stuff it. Shoot them,”
May 12, 2012 at 12:12 pm
Upon reflection I think I miscalculated the rate of 1.1. It’s possible under your vision of zombification to have a chain of 9 infections from the original infector, but in each case the infector dies, and you end up with one infection. I think this means you got 10 infections out of 9, with a case-fatality rate of 90%, and each person has only infected one other person before they die, so I guess that makes the reproduction rate 1 (without checking a text, the reproduction rate is the number of new infections each infection produces in its lifetime). So the disease would fade out in your case, but do so in a very aggressive way. An infection that kills you before you can infect someone else (which is essentially what the rage virus does in your description) is nasty as hell but not a big public health risk …
I often think about this problem when I watch zombie documentaries, because there seem to be an awful lot of semi-intact zombies roaming around, which implies that they got eaten by other zombies but only partially – if zombies are ferocious eaters of others, how come so many of their victims zombify instead of being eaten? The only way this works is if the zombies don’t actually want to eat much of you – they’re a kind of cannibalistic gourmet, sampling a bit of your liver and then moving on. But whenever they kill a lead character in a show, they seem to eat all of them. This is a big inconsistency. Especially in World War Z where there are millions and millions of pretty much physically intact zombies, trying to eat people. How did that happen?
Getting back to 28 Days Later, I’m pretty sure that in the sequel one of the characters was an asymptomatic infected carrier and the other carriers specifically refused to eat her – they could tell she wasn’t a susceptible. That suggests they can recognize the virus, and not by its symptoms but by its smell. I think that means it would be very hard to hide from them – they have strong hording tendencies and multi-sensory prey detection. Fortunately, they can starve to death…
May 16, 2012 at 6:54 am
Reblogged this on The World Building School on WordPress.com and commented:
This is a brilliant study on the theoy of zombie Hording. A MUST read for all would be zombie hunters and zombiepocalypse survivors.