Where once they shuffled, now they run. Initially born of forbidden voodoo rituals or the sign of a religious apocalypse, for the past decade zombies have slowly metamorphosed into the by-products of something else entirely.
Science now, not the supernatural, is most often to blame when loved-ones become something less than human and begin to prey on the survivors.
While earlier works of fiction have played with the notion of what a zombie is and how it comes to be, it is pop culture's modern influence on an ancient fear that has had the greatest impact on the undead's evolution.
But why?
God is Dead, But Science is Undead
"In so many ways, our supernatural gods have been replaced by technological wonders — so of course our monsters can't be far behind," Dr. Carolyn Kaufman, who has a doctorate in clinical psychology, tells Kotaku. "The god/monster duality reflects what happens when something we trust religiously turns on us. The pleasant propaganda (the so-called "good intentions") is shucked away in place of something hungry and mindlessly evil (the money-grubbing executives, for example).
"These days most people are not afraid that god is going to strike them down, they're more afraid that something in the medical world or pharmaceutical world is going to backfire."
And at the same time, Kaufman points out, science has helped to decrease peoples' fear of the supernatural.
"Science has demystified so much of that," she says. "But there is still is so much mystery behind what big corporations are doing. They have so much power and so much power in our lives."
And with this shift in perspective, this realigning of what is dreadful and frightening to the masses, comes a shift in how those fears are played upon in pop culture.
Books and movies had 28 Days Later, House of the Dead and The Crazies. Video games have Resident Evil, Dead Rising, The Secret World and, perhaps, even Left 4 Dead.
Fear of the Unknown
It turns out that Left 4 Dead, Valve's popular zombie apocalypse first-person shooter, hasn't quite yet spilled the beans about what caused their outbreak of the undead.
Valve's Chet Faliszek was surprisingly coy when we asked him exactly what gave birth to his games' zombies.
"While I appreciate your attempt to fish an answer out of me on how the Infection in Left 4 Dead started, we aren't giving that away yet," Faliszek said. "But in the (upcoming episode of Left 4 Dead 2) "The Passing" and the comic book coming out following its release, we will learn more on how the L4D Infection works and the implications of that behavior."
This ambiguity of the zombies' origins is deliberate, Faliszek says.
While the developer knows that people want "tidy" explanations for horrific events, Valve decided to avoid that. Instead Left 4 Dead tells its story through messages scrawled on walls and snippets of conversation, never really revealing what it is that we should fear.
What we can tell so far gives little indication of what caused the outbreak, but it does show that despite facing a ending world the survivors, at least initially, have little interest in discussing religion.
Faliszek points out that's because so far, in both the first and second games, the survivors don't have the time to sit down and chat really.
"They are all still rooted in practical survival," he said. "With the Infection sweeping the land quickly and our meeting the eight Left 4 Dead one and two survivors early in the Zombie Apocalypse, they haven't had a chance yet to think about anything but their survival or in the case of Coach; cheese burgers."
He adds that despite not knowing what it is that gave birth to the undead, the creatures still tap into deeper fears.
"They are more than just enemy soldiers, but a force on the world that is overwhelming," he said. "It is everything that can overwhelm you in life coming at you as one single clear enemy. Once the zombie apocalypse starts, you know the world is never going to go back to the way it was. You can't be a conscientious objector to the war on zombies, they are a force you have to fight or they will destroy you.
"There is also this feeling, while it is an overwhelming force working against you – if you play your cards just right, do everything perfectly, you can survive. It is up to you. It represents your daily life itself but in a clear and simple package."
World War II shooter Call of Duty: World at War, which features a surprise appearance of zombies in its multiplayer modes, also decided to be ambiguous about their zombies' origins.
"In Call of Duty: World at War, Nazi Zombies represent a fear of the unknown" said Josh Olin, Community Manager at Treyarch. "Their origin and biology is deliberately vague, a riddle to be solved by those who are interested.
Fear of the Supernatural
Of the video games out or coming out that feature zombies, only one seems to seriously look at the concept of these creatures being the by-product of the supernatural.
The yet-to-be released computer game The Secret World is a massively multiplayer online game set in a world deeply influenced by religion, said the game's creative director Ragnar Tørnquist.
"Religion plays a huge role in history and mythology, in modern conspiracies, urban legends and pop culture – it's something that affects all of us; politically, spiritually – positively and negatively," Tørnquist said. "It's an important part of the real world, and it's an important part of the secret world. Of course, our setting isn't based on a specific religion or set of beliefs – or religion in general – but it's a world where demons and vampires are real, where powerful secret organisations have ruled over mankind for millennia, where magic is everywhere and where the lines between the natural and the supernatural are thin. The spiritual – whether it's religion, the occult, or simply the fear of things that go bump in the night – fits right into that."
While publishers Funcom have been tight-lipped about how expansive the game will be, they have said that it will include modern day settings in New England, Egypt, New York, Seoul and London. All of which were researched to allow the game to tap into the local cultures' beliefs and traditions.
Among the supernatural creatures players will stumble across and fight will be hordes of the undead. Zombies that can be, Tørnquist says, categorized as supernatural. They are not born of a virus or bio-hazardous material, but rather mystical means, he says.
But despite that, Tørnquist and his team still aren't tapping into a fear or religion or religious consequences in their use of these creatures, but rather the ominous threat of a greater power in control of the undead.
"Our zombies play on people's fear of – and hope in – something bigger than ourselves, something ancient and mystical and spiritual that cannot be explained by science or technology," he said. "It's the idea of a world – a universe – of secrets, only a few of which we have deciphered. And there really is something terrifying and dreadful about seeing the dead being brought back to life by those who wish to destroy mankind – it's a slap in our collective faces and a great incentive for joining the war on darkness."
Fear of the Known
Like Dr. Kaufman, Tørnquist sees the move away from supernatural zombies as a response to a shift in public sentiment and fears.
"I guess it's the zeitgeist – the spirit of the times – to fear disease, pollution, technology gone haywire," Tørnquist said. "Zombies were traditionally supernatural; corpses reanimated through witchcraft and voodoo rather than victims of the superflu, but I think that most of us – at least in Europe and North America – fear a pandemic, global warming or a natural catastrophe more than we do dark sorcery."
This fear of science could always give way to a resurgence in religion and fears driven by the supernatural, mythological and religious. After all, Kaufman points out, a similar shift has happened before.
"Even centuries ago, technology seized the human imagination as a way to (accidentally) create monsters," she points out. "Take Frankenstein, for example, or Dr. Jekyll and Mr. Hyde. These authors argued that technology was giving humans the tools of the gods, and that humans were too flawed to handle it.
"These days I think people worry less about humans having the power of gods than about letting someone else have the power of gods. Absolute power isn't frightening unless it belongs to someone else. In the modern world, though, lots of entities have overwhelming power over our daily lives — the drug companies, the Apples and Microsofts, and so on."
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Chet over at Valve just sent us this sweet personalized Zune with fancy Left 4 Dead 2 engraving to give away on the site.
A video broadcast to U.K. Xbox Live subscribers confirms suspicions that Left 4 Dead 2's "The Passing" DLC 
Valve's poster for Left 4 Dead 2's The Passing downloadable content finally gets a tagline: Nobody Survives Forever. And while the original survivors will be showing up at the beginning of The Passing, only three make it to the end.