Zombies are a big deal in pop culture now. In the past week maybe it was watching Cabin in the Woods, or playing State of Decay, or talking about the Walking Dead that got me thinking about just how many zombies could the world have. The answer really depends on the type of zombie. If you’re talking about a plague that turns the living into cannibalistic, infected monsters then the number is limited by the population of the Earth. So the maximum amount is about 7 billion zombies, the world’s population. Of course, this number would be lower due to the number of people that would be completely eaten and decimated by the hordes, but its a good theoretical max.
But what about the more traditional zombie? Maybe from some kind of black magic or outer space radiation causes dead bodies to rise from their coffins and dig their way to the surface. How many zombies are we talking about now?
While researching I came across the incredibly terrible statistic that there are more people alive right now than have EVER lived before. This is completely untrue. Completely untrue. So untrue, that its embarrassing that people think its true. In just World War 1 and World War 2 alone the total casualties were about 1 billion dead, which is one seventh of the current population. The idea that more people are alive now than ever has been in the history of humanity is so annoyingly, ludicrously wrong. But, I digress.
So, if the total zombie army could be every single person that ever lived and died in Earth’s history, how do we even begin to calculate that number? Turns out the Population Reference Bureau already figured that out, albeit they did it for reasons that did not include a zombie apocalypse. After creating a comprehensive population growth model since the dawn of human existence and using what they refer to as “guesstimates”, the number settled upon was 108 billion people that have ever lived. They use the term guesstimates, because for 99% of human existence there is no concrete data available. Take a look at this article for a more in-depth look at what the PRB did (http://www.prb.org/Articles/2002/HowManyPeopleHaveEverLivedonEarth.aspx).
108 billion zombies. Wow. Except, there is one last thing to consider, decomposition. Even if there are 108 billion humans that have lived and died many have decomposed into dust. We do have a long fossil record of human remains, but these are the rare samples that were preserved in some way. How fast does decomposition happen? As it turns out, after a year all that is usually left from a body are the bones and teeth (but this time frame varies based upon what is done with the body). Bones take an extremely long time to dissolve, depending on where they are located (soil, coffin, etc). The process could take between 25 to 500 years.
To find a final estimate of a total zombie population the PBR data will be used, and a maximum and minimum will be found. The minimum will only consider those that have died in the previous year, because of decomposition rates. After some research I found the estimate that 56 million people die every year. Adding this to the Earth’s population we have an undead army that would hit around 7.5 Billion Zombies minimum.
The maximum will consider undead skeletons rising alongside their zombie counterparts. Since the data is broken into 50 year intervals on the PBR website, we’ll only consider the world’s population since 1950 for the max. This estimate seems to be the most appropriate when considering rates of decay, because after fifty years the bones would be much too brittle to work despite whatever magic is involved. The maximum number is about 25 Billion Zombies. Again, these numbers are just quick calculations, but those numbers are pretty crazy. Since I have zombies on the brain (pun intended) I might follow this up with an entry about how a zombie epidemic spreads, because there’s a lot of cool research available on that topic.
Nice article here. When I was reading it, everytime I found myself thinking, ‘ahh but you haven’t taken this into account’, you went on to cover it in the next paragraph.
If you do look into how zombie epidemics spread, you should read Robert Smith?’s (the question mark is meant to be there) excellent 2009 paper on the subject (it’s titled ‘When zombies attack!: mathematical modelling of an outbreak of zombie infection’).
If you’re looking for other zombie-related maths stuff, I’ve got a blog called ‘Maths With Zombies’ where I post relatively simple maths problems based on different zombie-related scenarios.
If it sounds like something you’d be interested in, check it out at http://mathswithzombies.wordpress.com).
If not, you should definitely check out the Robert Smith? paper.
That’s a pretty cool blog – I’m a (future) teacher, and I can see myself using something like one of those problems in the classroom.
Glad you like it! I think involving zombies is potentially a great way to engage kids who would otherwise feel excluded because of the way maths is usually presented to them. Feel free to use them as you see fit and I hope they prove useful. However, you need to always make sure any school you’re working in is happy with you using zombie-based materials before you do so (some can be a bit off about it!)
Nice!! Those are quite scary numbers, but you might consider that plagues spread quite slowly (have you ever played “Plague.Inc”? It’s a nice game n.n) and humans can be eated faster than infected, because even the infection takes time (just watch “Night of the Living Dead”)… so even if every zombie eats only one person each, the Earth will host 3.5 billion zombies by the end of the apocalypse, and those zombies will die 25 years after erradicating humanity.
…But we still love zombies, don’t we? hahahahahaha 😀