The Zombie Survival Guide
Zombies are a pop culture phenomenon. Lumbering, flesh-eating corpses have grabbed the spotlight from the sexier, scarier vampire and become the ‘it’ monster of the age. From sex on legs to putrefaction on legs.
What is a zombie?
Your standard zombie is a mindless monster with an immense appetite for human flesh. Their sole purpose is to kill, eat or infect people, and often show signs of physical decomposition, such as rotting flesh, discoloured eyes, and open wounds. Often, they shuffle with small, irregular steps, such as in Shaun of the Dead, as a nod to the rigour mortis stage, but many video game zombies can sprint, climb, and even jump, such as those in Days Gone. Those ones are the worst.
What unites most zombies is the end game: the decimation of the human race via zombification.
In a post-apocalyptic world brought on by a highly contagious zombie virus, survival is key.
Get lost
Davide Cassi, Universita di Parma, investigated how long an entity hiding in a complex structure could survive if being pursued by ‘predatory random walkers’; not zombies, per se, but we all know he meant zombies. Cassi described a general principle of a prey’s likelihood to survive over time while hiding in an irregular structure, like a large shopping mall, and found the likelihood of survival is closely related to how complex the hideout is. In structures with plenty of twists and turns, the chances of the predator coming into contact with you shrinks down to almost zero.
Do the maths
Robert Smith, University of Ottawa, wrote an actual book titled Mathematical Modeling of Zombies. He showed that a zombie infection would spread quickly (real Coronavirus vibes here) and that there’s no possibility for a ‘stable equilibrium’ where humans could coexist with the undead or eradicate the disease. The maths quite simply show we’d be quite quickly fucked.
(bN)(S/N)Z = bSZ
Where N represents the total population, S the number of susceptible people, Z the number of zombies and b the likelihood of transmission.
Admittedly, this equation is a bit delicate. The total population could be the population of living people and assuming no innate immunity, the total population could therefore be equal to the number of susceptible people. If the zombie outbreak is of the reanimated corpse variety, the total population figure needs to include the number of corpses in a viable (read: not so decomposed) state to claw their way through the ground to lumber after our brains.
The dead aren’t usually a dynamic variable.
We’ve seen efficient killer diseases before—the bubonic plague (the Black Death) of the 14th century was pretty effective—but the scariest thing about the zombie plague is the fact that zombies could possibly continue their undead existence for hundreds or thousands of years. Do they keep decomposing as they wander the earth a la The Last of Us? Or do they maintain a consistent condition indefinitely? Max Brooks’ zombie type is susceptible to the natural process of decomposition but the Solanum virus infecting it keeps the decomposition bacteria and other organisms at bay for years, making its decomposition rate extremely slow.
But, in most pop culture examples, zombie-ism spreads fast. In World War Z, for example, Brad Pitt’s character counts the seconds from bite to zombification. Not the days, months or years, but the seconds. Plugged into Smith’s model, that high infectivity makes a zombie epidemic practically unstoppable.
It only takes one zombie to overtake a city.
If the laws of nature apply to zombies too, a single zombie would cease to be an active threat after four days. But this only pertains to a single zombie, not a horde or a city of them. If the rate of infectivity of World War Z is combined with the usual trends of first report, cover-up, increasing frequency and then outbreak, the point of outbreak would be almost instantaneous. Infection would be rapid and uncontrolled and large portions of the population would be infected almost simultaneously. Four days would be more than enough time for the virus to run rampant and for the living population to be almost eradicated.
Jane Heffernan and Derek Wilson, both of York University, modelled the likely survival rates of a zombie plague using data gathered from various zombie films, including Night of the Living Dead and 28 Days Later. They found that in the event of a zombie plague, humanity’s days are numbered and mankind would last around a month. The sheer number of the undead, their longevity in death and the efficient transmission rate combine to spell our doom.
Neither quarantine nor a slower disease progression could stop a zombie apocalypse—only delay it. To save humanity, more violent, head-destroying methods would need to be employed.
Braiiiiiiiins
If you are waiting on the waiter to bring your food, does that not make you the waiter? Similarly, if the only way to kill a brain-craving zombie is to destroy its brain, does that not make you the brain-craver?
One model developed by Alex Alemi and Matt Bierbaum of Cornell University assumes that zombies are 1.25 times more effective at biting humans than humans are at killing zombies. That number should probably be much higher.
Killing a zombie is hard. You have to be a good enough shot to get the head, usually when your target is moving, or you have to get close enough to smash its brains in with whatever implement you wield.
A group of students at the University of Sheffield used an SIR model (Susceptible, Infectious, and Recovered) to show how attempting to fight the zombies would lead to more people being infected and coming back as a zombie. Sending in the military was another option they considered but this lead to the same output.
We can use tanks and firearms, build fences and moats, collaborate and think to protect ourselves. But zombies don’t need to sleep and don’t need to eat. They have no motivation other than feasting on our brains and no distractions from said objective. And, pretty quickly, they have the sheer numbers. One zombie versus one human is a no-brainer (pun very much intended) but a thousand zombies coming for one human? No brain for the human in that scenario.
Okay, but really
Zombies are walking representations of contagious disease: they spread their affliction by munching on the healthy.
‘A zombie is a bit like giving a virus legs and teeth,” explained Ian MacKay, a virologist at the Australian Infection Diseases Research Centre, University of Queensland. ‘It’s basically a virus taking over a host, and spreading very quickly and efficiently.’
Modelling a zombie outbreak gives scientists a look at how human behaviour affects pandemic models in an urban landscape. If a virus did appear to cause healthy people to turn on infected people due to fear (hello Coronavirus), thought experiments like this can help scientists and governments in the future.
Hefferman and Wilson of York University stress that the tools they used to model a zombie plague are the same used to model future disease pandemics. They use the unlikeliest of scenarios to gain insight to the trajectories of unknown diseases. They contribute to humanity’s arsenal against the unexpected by simulating the undead.
Smith of the University of Ottawa knows that zombies don’t exist but points out that modelling something that doesn’t exist, like a potential disease, can be made much more interesting by testing it on zombies. ‘You still have to understand what you’re going to do,’ he explained. ‘Are you going to close schools, are you going to quarantine, are you going to lose the whole of society to this outbreak?’
Modeling things that aren’t real help us prepare for things we weren’t expecting.
‘Once you’ve tried modelling zombies,’ says Smith, ‘you can never go back.’
As the Zombie Response Team says,
‘If you can survive a zombie apocalypse, you can survive anything.’ ■