7.
They Have Too Many Natural Predators
Now consider the poor zombie. It lacks every single advantage that has kept humanity from being eaten to extinction. It wanders around in the open, it can't use weapons, it can't think or use strategy. It doesn't even have the sense of self preservation to run and hide when it's in danger. And, it's made entirely out of food. It's easy prey for any animal that wants it. Insects are a major pain in the ass for living humans, and in some cases, being able to swat away flies and having an immune system is the only thing keeping us from having our eyes and tongues eaten out by maggots. Zombies in any part of the world with a fly problem are going to be swarming with maggots in short order, meaning that most of their soft tissues will be infested, and their eyes will be very quickly useless. We'll scale up a bit: In America alone, we have bears, wolves, coyotes and cougars, all of which can put well-armed, thinking, fast-moving humans on the menu, if the conditions are right. To most predators, the "right conditions" are when the animal is weak or infirm, or otherwise generally unable to defend themselves, like a walking corpse. Hell, just think of the millions of stray dogs out there who'll quickly learn that zombies are an easy meal. Now imagine zombie hordes wandering Africa. Between lions and cape buffalo (and hippos, and rhinos, and elephants), we'd finally have a disease that Africa is better suited than the rest of the world to defend itself against.
6.
They Can't Take the Heat
It's generally accepted by zombie experts that they're going to continue to rot, even as they shamble around the streets. What the movies fail to convey, however, is the gruesome yet strangely hilarious effect the hot sun has on a rotting corpse. The first concern is putrefaction. Thanks to the plethora of bacteria we use in our colon for digesting plant matter, called gut flora, our bodies are ripe for decay the second our heart stops. Since heat speeds the growth of bacteria (which are plenty happy to start feasting on you once your immune system is no longer a concern) the zombie's got a looming expiration date the very second it turns. The warm, moist conditions in the tropical and subtropical parts of the world (or even just summer in the temperate parts) speeds this condition, meaning a July zombie outbreak pretty much anywhere would be over in a few weeks just by virtue of the rampaging monsters bursting like rancid meat balloons. At the other end of the heat spectrum is dry heat. If you're in Phoenix or the Sahara when the apocalypse hits, the zombies might begin to mummify in the blazing sun and heat. While the normal symptoms of dehydration are not a concern for a zombie, there is the problem of desiccation. With no reasonable means of replenishing the water in their cells, zombies walking around in the Texas heat all day are going to suffer cell damage due to direct sun exposure to their skin, and thanks to the drying effect wind has, the Southwestern dead will stumble around more and more ineffectively until, at some point, they simply drop and wait for the scavengers to come pick them up for the annual Slim Jim harvest.
5.
They Can't Handle the Cold
Unregulated cold does awful things to formerly living things. If you live far enough north, the zombie apocalypse will probably work itself out the first time it tries to go outside. The first zombie-killer is the simple fact that the human body is mostly water, and water freezes. Once the temperature drops to freezing (or near it with a high wind chill), zombies will become significantly more rigid.
4.
Biting is a Terrible Way to Spread a Disease
Hey, remember that time when that dog got rabies, and then a day later, every single other dog on the continent had it, except for a small band of survivors huddled in a basement? No? That never happened? Nearly all of the zombie movies agree on one thing: They reproduce like a disease, one that spreads via a bite from the infected (like they have a virus carried by zombie saliva or whatever). But this also means their spread should be subject to the same rules of a normal epidemic, and biting is a crappy way to get an epidemic going. The successful diseases have some really clever way to invisibly spread from victim to victim. The flu has killed tens of millions because it floats right through the air, the black plague was spread by fleas, etc. Not a single one of them requires the infected to get within biting distance to spread their infection. Sure, sexually transmitted diseases like AIDS work that way, but that's only because the infected can pass for the uninfected. Nobody is going to be having sex with a zombie. Though Google Image Search does turn up a large volume of zombie porn But let's say there is an outbreak, like if one zombie was able to bite 30 people in the crowd at an Insane Clown Posse concert before they figured out it wasn't part of the show. It's not like mankind is just utterly confused about what to do when an infection breaks out. In America you have the Center for Disease Control (CDC,) who don't tend to screw around. Seriously, it's on their business cards. Remember the SARS outbreak? That originated in China. The CDC and the World Health Organization put the clamps down on international travel the second it was found to have spread to North America. Flights were grounded, travel between borders was locked tight and only 43 people on the entire continent died. No one was overlooked. With zombieism, they don't even have to solve the mystery about how it's transmitted. It's that guy biting people. Shoot him in the head.
3.
They Can't Heal from Day to Day Damage
One advantage to having a fully-functioning central nervous system is that it also does a damn good job of letting you know you've been damaged. It does this by way of pain. Think about all the paper cuts, stubbed toes and nut shots you have suffered in your life. Now imagine they never healed, just sat there and rotted while you continued to rack up other paper cuts, stubbed toes and nut shots. Pretty much every wound you've ever had would end with an amputation. One thing we know about zombies from Romero and Fulci is that they are a clumsy lot, walking into doors and helicopter blades without a second thought about what kind of damage they are suffering. While complete insensitivity to pain seems like an awesome superpower in theory; in real life, you wind up being more like Mr. Burns than Wolverine. Congenital insensitivity to pain is a neurological condition that some people are born with, meaning they don't feel pain. They can feel everything else, but the absence of pain means they accrue damage to their bodies but are unaware of it. Even with the ability to call for help, loved ones watching out for them and our coddling society, this can still lead to all kinds of terrible stuff, like infected body parts and bitten off pieces of tongue. All the dings and bangs zombies will suffer after tripping, walking off of bridges and stumbling around on dark cloudy nights will eventually leave them limbless, toothless and with every bone in their body broken.
2.
The Landscape is Full of Zombie-Proof Barriers
The zombies' lack of coordination, along with the inability to see in the dark (we haven't had any infrared zombies yet, but holy crap! We call dibs on the idea) is going to spell the doom of countless zombies in any area outside of a parking lot. This is a group that doesn't know how to find roads or bridges. They just go wandering off aimlessly. Mountains, major rivers and canyons would thus quickly be home to piles of broken zombie rags stinking up the scenic views. Even if zombies had the foresight to not walk over cliffs or into raging rapids during the day, nightfall would result in most eventually walking into rivers, over cliffs and off of bridges, diminishing their numbers. But even in nice, flat, paved cities, where it would seem like people would be extra-screwed, the landscape still works in favor of the living. History has shown that in most awful situations, people don't always act like the panicky idiots in a horror movie. In cities, people would likely congregate in the upper levels of high-rise buildings, where the invasion can be held at bay with simple security doors. Also, the streets themselves would keep the undead corralled in straight, easy-to-aim-down lines where they could be picked off by snipers, or just bored office-workers waiting out the quarantine by dropping office supplies onto the undead from the top floors.
1.
Weapons and the People Who Use Them
Add to the mix the sheer number of armed rednecks and hunters out there, and the zombies don't even stand a chance. There were over 14 million people hunting with a license in the U.S. in 2004. It's safe to assume that when the game changes from "three deer" to "all the rotting dead people trying to eat us," there will be no shortage of volunteers.Plus, if we look at zombies as a species, they are pretty much designed for failure. Their main form of reproduction is also their only source of food and their top predator. If they want to eat or reproduce, they have to go toe to toe with their number one predator every single time. The zombies have no choice but to walk into bullets. And all this isn't even counting all the other household hand guns in the world, nor the fact that zombies also have to contend with IEDs, Molotov cocktails, baseball bats, crowbars and cars that the general public will no doubt be using to cull their numbers. And that's just from the civilian population; counting the military and police, we have another three million or so armed people, and instead of just handguns shotguns and hunting rifles, they have machine guns, combat shotguns, sniper rifles, assault rifles, sub-machine guns, grenade launchers and the occasional taser, not to mention the training to use them effectively. But why would they even bother? When they could just roll over swaths of zombies in tanks, blast them with cluster bombs and MOABs and mow them down with miniguns from the *&$@$#! Air Force that every zombie flick seems to forget about.
