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Mathematical models give little hope for mankind's survival in a real zombie apocalypse

Mathematicians and a psychiatrist have crunched the numbers, and our chances seem bleak if someday we encounter a virus of the Living Dead

PUBLISHED : Sunday, 14 July, 2013, 12:00am
UPDATED : Sunday, 14 July, 2013, 1:49am

There are the turbo snails in this summer's kid flick hit called Turbo. Then there are the turbo zombies in World War Z, the latest Hollywood zombie movie starring Brad Pitt looking like a reanimated Kurt Cobain.

Instead of the traditional walking dead with unsteady decaying feet, the undead now come running and leaping. Many critics have lamented this trend, which breaks the canonical law of zombie locomotion, established by George Romero in his 1968 classic, Night of the Living Dead. As Max Brooks, who wrote the novel on which Pitt's movie was based, has noted, "the fastest [zombies] have been observed to move at a rate of barely one step per 1.5 seconds." They are supposed to be slower than practitioners of tai chi.

The emerging characteristic of deadly zombie speed has serious implications in that it invalidates two pioneering studies. One explores the possibility of a zombie virus existing in the real world; the other calculates the probability of humanity surviving such an outbreak: both studies assume the zombies would remain stumbling and shambling.

Two years ago, Harvard psychiatrist Steven Schlozman published The Zombie Autopsies, a novel based on scientific facts. Using examples from real-life brain-destroying diseases such as mad cow, he argues a zombie virus is possible. He calls the virus ataxic neurodegenerative satiety deficiency syndrome, or ANSD. It destroys all the brain's key parts except the amygdala, a part of the limbic system responsible for the fight- or-flight response.

Zombies always fight because of their insatiable appetite following the destruction of the ventromedial hypothalamus, the part of the brain that tells you when you are full from eating.

They can't think or make decisions because their frontal lobes, responsible for problem-solving, have been devoured by the virus. And they can't walk or move properly because the cerebellum, responsible for motor control, no longer functions. Presumably, however, the brain stem, which regulates breathing and heartbeat, survives the virus.

You can see that the new zombies have already overtaken Schlozman's brain model. They are not only running faster, but are getting smarter and becoming self-aware.

In Romero's Land of the Dead, released in 2005, the zombies are evolving intelligence and even a moral sense of telling right from wrong. Someday soon, Romero's zombies, the smartest ones anyway, will be devouring Kant's Metaphysics of Morals as well as human flesh. In this year's Warm Bodies, our zombie movie hero named R has even developed a love interest in a human female and helps her and her friends survive.

All these may be accounted for in a notorious study by four mathematicians at Carleton University and the University of Ottawa. In 2009, the Canadians published epidemiological models to predict various survivability scenarios in a zombie apocalypse. One model assumes a cure, a scenario that may be taken to resemble the situations in the Land of the Dead and Warm Bodies whereby zombies are becoming more human-like.

Despite these maths geeks' apparent frivolousness, their innovative models have been adopted by epidemiologists and several health authorities to study the spread of real-life human papillomavirus, or HPV, in a population. Such epidemiological models are the bread and butter of frontline organisations such as the US Centres for Disease Control and Prevention and the World Health Organisation in tracking the spread of emergent and highly contagious diseases.

According to the zombie mathematical models, the odds for humans are not good. They predict that the introduction of a single zombie in a population of half a million is enough to kill or turn everyone into a zombie in just one week. And this is from assuming the classical slow-moving variety, not the new zombies in a hurry.

From a basic model of bite-and-infect, the mathematicians develop more realistic scenarios such as a model with a latent infection period of up to 24 hours - in World War Z, this can be as short as 10 seconds; a model with quarantine; a model with a cure; and a model with a full-scale attempt at eradicating the zombies with whatever resources are left.

The first four models are unstable, meaning humans are unlikely to survive or co-exist with zombies for long. Only the last one, complete eradication, offers a realistic chance of survival. But the authors observe that by the time the authorities realise the need for, and can muster, a concerted eradication response, the time lag will lead to considerable degradation of available resources and capabilities. In short, it may already be too late.

World War Z the movie has a relatively happy ending, as you do with a typical Hollywood movie. But that is more hopeful than real. The treatment that the Pitt character discovered was not even a cure. Given the zombies' new mobility and contagiousness, our chances of survival would be virtually zero.

Alex Lo edits the Science page

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