Nuclear Mutation
The Chernobyl disaster is proof that radiation causes genetic mutation in the surrounding wildlife, but did not have an effect directly on the workers. It did however, effect the birthed children. Higher radiation doses caused by, for example, an atomic bomb during World War III, could result in human mutation.
The risk: Very low. While World War III is imminent, it remains to be seen where it will begin and which weapons will be used.
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Virus Mutation
Whether it be the recent swine flu (H1N1) or a strain of rabies, it's
a very possible scenario. The flu can mutate many times over the period of a flu
season. Rabies can mutate as well.
The risk: Low. While the flu can mutate, even at pandemic levels it doesn't spread rampantly enough. While current strains of rabies cases generally transfer through animal-human contact (and on rare occasions, human-human contact), a simple genetic mutation could change everything.
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Prion Mutation
Creutzfeldt-Jakob disease (the human version of mad-cow disease)
Symptoms include:
Changes in gait
Hallucinations
Lack of coordination
Muscle twitching
Myoclonic jerks or seizures
Rapidly developing delirium or dementia
Now, most humans who contract Creutzfeldt-Jakob disease don't necessarily want to eat each other, but all it would take is a strain that releases serotonin into the brain, and voilà, 28 Days Later.
The risk: Medium. All it would take is a higher-evolved disease similar to mad cow to infiltrate our food supply.
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Nanobots
A group of chemists at the University of Nebraska were able to piece together a living cell fixed to a structure of an electronic device. Soon, nanobots will be used as a tool to continuously live inside of your brain to replace damaged neural connections with new ones. An interesting fact is that this cyborg can continue to live up to one month after the host expires; this includes a continuation of it’s own neural pathways, meaning it could continue to move your limbs, even post mortem. Even creepier, nanobots can continue to self-replicate themselves. Nanobots would be able to acknowledge needing a new host; this could be accomplished through a bite, thus releasing millions of nanobots into the next body.
The Risk: High. Nanobots are extremely dangerous, as scientists are aware. However, this is not stopping them from continuing research on the most probable cause of the extinction of the human race.
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Neurotoxins
There are already cases of this throughout our history. Using a specific cocktail of poisons (including poison from a Japanese blowfish), one is able to slow down all bodily functions, to the point that some doctors would even classify the person as dead. Then you can bring the person out of this trance-like state with a chemical alkaloid, which leaves the host with no memory but they are still able to perform simple tasks (eating, sleeping, basic physical activity). The only problem with this theory is that alkaloids don't trigger violent behavior, and no chemical concoction has been found to induce violent behavior -- yet.
The Risk: Very high. Just read about Clairvius Narcisse. All it would take is a specific mix of poison to induce violent behavior and Romero's dream would become a reality.
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