When Vulture asked me if I, who earned my Ph.D. studying the physics of DNA, would be willing to watch World War Z from a scientific perspective, I figured they just wanted someone to play the part of a cold-hearted Professor Frink–esque math guy who only finds joy in deconstructing the science in films. But just because I now use lasers at work to study how cells generate force to divide doesn’t mean I can’t accept and enjoy zombie-apocalypse cinema on its own terms.
That said, they picked the right guy, as a couple of thoughts about scientific accuracy and plausibility occurred to me while watching World War Z over the weekend. I’ve recorded those thoughts to the best of my abilities below. Now, it should be noted that I’m not an expert on zombies, per se. Also, because these are science thoughts, they’re not funny, which probably isn’t the preferred delivery system for this sort of topic (but is totally par for the course in my profession!). Anyway, here are a few things that came to mind as I watched the film. (Some spoilers below for those who haven’t seen the film.)
In the movie, the total onset of the zombie disease takes about twelve seconds and is sudden and total (meaning the whole body responds instantly, rather than with a slow creep). In reality, it takes about a minute or so for blood to circulate through the body in an average person, and if the infection is viral or biological, it would take quite a bit longer for the machinery of those pathogens to start inducing an immune response. Chemical compounds, which are small and can diffuse quickly, are able to produce a more immediate effect, but twelve seconds is probably still too short a time to do so effectively. It’s clear the zombie disease affects the nervous system (i.e., muscle control is altered and the zombies become twitchy, and we’re led to believe the entire brain is overcome when the zombie “switch” is turned on) all at once. A more realistic depiction would have the symptoms emerging over time. Then again, if I remember correctly, we’re told that the infection is not viral or bacterial in nature and is instead some unknown pathogen, which perhaps acts in a completely different manner. However, the rapid and sudden total onset of zombie-disease is not terribly realistic, especially given that it’s rewiring the nervous system in a pretty major way.
The WHO research facility
This lab space was actually quite realistic. It was obviously a very well-funded lab, as the equipment and building space were nice and shiny, but this layout was entirely plausible. It’s usually the case that such deadly pathogens would be kept in a separate and more secure area as shown in the film, but usually there’d be a lot more obvious ventilation and biohazard suits to deal with those kinds of things (typically, a separate room you’d enter to suit up, then a further secure room to do work). Also, it’s probably not the case that every deadly pathogen known to man would be sitting in a rack in the same fridge, all thawed and ready to use. But given the unique urgency of the zombie situation, it’s possible the scientists were cutting a bunch of corners. In any case, this lab space was definitely not of the CSI, neon-lit variety (that does not exist anywhere I’ve ever been) but was instead reasonably accurate.
One of the coolest scenes involved that swarm of zombies scaling the wall into Jerusalem. This was kind of foreshadowed at the beginning with brief images of ants and bird flocks. There’s a phenomenon in biology called self-organization, which basically refers to the notion of individual components following a few simple rules in order to create a larger structure that has the appearance of design. This happens on all kinds of length scales, from within the cell (the mitotic spindle in cell division) to whole populations (schools of fish and flocks of birds). In these examples, individual components (such as a protein or a single bird) are merely following a simple cue in their local environment without any concern for or intention to follow a bigger plan. However, as a whole group of these individual components interacts in this way, a large, ordered structure can emerge. The relevant point here is that the zombies didn’t need to lay out a strategy and design a plan; by simply responding to their local cues (loud noises that way!), this large and effective structure emerged.
Despite the obvious fact that inducing meningitis in an entire population seems like a poorly thought out short-term plan, the notion of prey making themselves undesirable to predators is a fairly common strategy in nature. Animals that play dead to appear unappealing as a meal and those that emit odors to suggest decay and illness are fairly well known — see possums, skunks, etc. Humans have a disgust response that also guards against infection (like how the smell of rotting meat alerts us that we’ll become ill if we eat it — although the meat itself isn’t doing that to protect its personal well being, so maybe that’s a weak example). What was a bit puzzling was the method of detection of infected prey. The zombies, of course, are using the human body and its built-in capabilities as their hosts, kind of like parasites. This means they are kind of stuck with our bodies’ innate abilities to sense the environment. They can obviously hear quite well, and that’s presented as the major form of stimulus throughout the film, and their vision seems to be in decent shape, too. But it’s completely unclear how they are able to sense an individual that is infected with some sort of illness. Smell? We see the zombie sniffing intensely at Brad Pitt, but the human olfactory system isn’t terribly sensitive. Maybe the zombies have rapidly developed super-smell abilities? Also, someone who has injected himself with a known virus or bacterial strain (it was unclear which one he chose in the movie, although we know the vials on the left rack were super deadly, but the vials on the right were only kinda bad — nice job flipping that coin, Brad!) would take way longer to develop obvious symptoms, such as a visually identifiable sickness or an odor that the human nose could detect. As an aside, there has been research done demonstrating that dogs, whose noses are extremely sensitive, can detect certain kinds of cancer, in a controlled setting. So, if these were zombie dogs, I’d have an easier time buying this whole “cure” strategy. Any other form of sensing the presence of infected prey, unless they just kind of know it preternaturally or something, would require methods we’re not currently aware of.
I also found it interesting that the zombies don’t consume their human prey; they bite once and quickly move on, without stopping to relieve any of their victims of their precious nutrients. This strikes me as a terrible survival strategy. Those zombies are hauling ass really fast all over the place! How do they replenish their energy? They should be getting tired, right? When there’s no humans around, they’re standing still in a dormant state, which of course conserves energy, but they appear to have only one biological instinct: to reproduce via biting. Do they get hungry? Thirsty? Shouldn’t the humans just hole up somewhere for a bit and wait for these things to keel over from malnutrition, rather than sticking everyone with meningitis?
About the author: Scott Forth received his Ph.D. in physics from Cornell University and is currently a post-doctoral fellow at the Rockefeller University in New York City.