The breakdown of society as the result of a rapidly spreading zombie outbreak, a so called zombie apocalypse, is today a popular theme in many novels and movies. This popularity leads to many spirited debates betweens fans of the zombie genre, arguing over the effectiveness of the military, the likelihood of surviving, etc. Maybe you, dear reader, have even read the oft-cited paper "When Zombies Attack!: Mathematical Modelling of an Outbreak of Zombie Infection", the conclusions of which I will be rejecting.
To answer the question of whether or not humanity would survive a zombie apocalypse, many false preconceptions must first be addressed. To begin with, ask yourself this, when was the last time than one human contracted a disease which then spread until every human being was dead except a small group of people huddled in a basement? The answer is of course never. While zombies (whether slow or fast) pose a unique danger when compared to other viruses, the zombie pandemic as a whole can still be considered as a virus.
The idea that zombies are just a virus leads to a number of important conclusions. Firstly, while the zombie virus (Z virus from here on) could be transmitted to a living person through a bite, scratch, or in the air, a healthy person who died, say in a car crash, could not then become a zombie because it is impossible to make a dead person sick. This means that if, for example, a person is bitten by a zombie and bleeds out before the Z virus can infect them, they will not themselves become a zombie.
Secondly, like any virus, the Z virus would not be capable of infecting someone in ten seconds but would instead have an inoculation time of at least a few hours. Whether the virus infects then turns the person into a zombie, or just makes the person a carrier waiting to die from a car crash or zombie bite so as to become a zombie would depend on the Z virus. Though this means that there could be many non-symptomatic carriers of the Z virus, it also means that there would no people instantly succumbing to a zombie scratch (though if they were infected and died in a car crash they could instantly become a zombie).
Thirdly, because the zombies are basically dead people, there would be no way to cure them since it is also impossible to cure a dead person. A vaccine is of course not of the table for those people who are still healthy, though a vaccine may not cure a non-symptomatic carrier (and a virus can't be cured by medication).
These conclusions certainly reduce the imagined threat a potential zombie apocalypse could pose to humanity's survival. However, the fact that zombies, like any virus, must by definition die off relatively quickly (see the peak in the Spanish flu graph above) is their single greatest weakness. Zombies expend a lot of energy chasing people. Even if its rotting body can replenish its energy by somehow managing to eat and digest human flesh, the fact remains that the body is still rotting. Nature is incredibly efficient at decomposing dead things, a category in which zombies are the most active members. In addition, decomposition in the air is twice as fast as in water and four times as fast as in earth. Within a month the vast majority of zombies created in the initial outbreak would be nothing more than piles of meat. If the Z virus produces zombies that are not actually dead (i.e. not rotting) then these undead will starve, probably in less time than the process of decomposition would take.
This is the reason why I'm rejecting the conclusions of the paper "When Zombies Attack!: Mathematical Modelling of an Outbreak of Zombie Infection". In this paper, zombies don't die off naturally but rather are only killed by survivors: "zombies move to the removed class upon being ‘defeated’. This can be done by removing the head or destroying the brain of the zombie" (Munz, Hudea, Imad, and Smith? 135-146). This leads the authors to conclude that the only way for humanity to defeat a zombie apocalypse is by aggressively exterminating the undead. Though this could be an effective strategy, depending on the number and type of zombies produced in the initial outbreak it could be a much better idea to simply hunker down and wait for the hordes to decompose.
So could a zombie apocalypse mean the end of humanity? No, not even if the initial outbreak is very rapid, thereby avoiding the issue of decomposition. Such an outbreak would require a very potent Z virus, one transmitted by bites, scratches and the air that is capable of killing people and that also creates fast zombies. The faster the outbreak the less time humanity has to react: the military is crippled and a large chunk of the world's population is killed.
However, as a species we have survived an assortment of brutal pathogens. The black plague killed 15-25% of the world in the 14th century; it took 150 years for the population of Europe to recover, yet it still managed to. Small pox's 20-60% mortality rate killed 300-500 million people in the 20th century alone, yet humanity managed to eradicate that disease in 1979.
Of course, a major zombie pandemic today would be hitting a population highly concentrated (50%) in cities and not cultivating its own food. Yet our advanced technology and shear numbers (99% death rate and there'd still be 70 million humans spread out across the globe) play to our advantage. When all is said and done, the experts agree that it is far more likely that humanity will destroy itself than be killed by an unprecedentedly massive pandemic.
Munz, Philip, Ioan Hudea, Joe Imad, and Robert Smith?. "When Zombies Attack!: Mathematical Modelling of an Outbreak of Zombie Infection." Infectious Disease Modelling Research Progress. (2009): 135-146. Web. 8 Jul. 2013. <http://mysite.science.uottawa.ca/rsmith43/Zombies.pdf>.
for a zombie movie review, please see