Forced Evolutionary Virus

The Forced Evolutionary Virus (FEV) is, aside from radiation, the other major source of mutation in the Fallout world. Most importantly, super mutants and the Master are a result of FEV infection. Aside from super mutants, the Master also created a variety of other creatures. No one is sure where the floaters came from, but then again most would rather not know. Centaurs were created by tossing a varied mix of dogs, cats, brahmin and other animals into a vat and seeing what came out the other end.

Before the War
In the years leading up to the Great War between China and the United States, both sides were scrambling to research something that would give them an edge in the coming conflict. What the Chinese research teams developed is unknown, but America tapped its resources of private industry for a secret weapon to beat the Chinese. One company, a high tech outfit called West Tek, was a major defense contractor. In the first Fallout, the player explores a location called the Glow, which is in fact an underground West Tek research facility that was directly targeted by Chinese warheads during the War. While exploring the heavily radioactive ruins, the player discovers that West Tek created a number of useful things for the American military. Laser and plasma weapons were being experimented with here. Power Armor, massive self-contained suits that turned a single soldier into a walking tank, was developed here. And most importantly, some terribly important research into immunity drugs was being conducted at West Tek.

One fear among the US military was that the Chinese would deploy biological weapons against American troops: powerful superviruses that would decimate armies without a single shot fired. Thus, West Tek began the Pan-Immunity Virion Project (PVP) to develop a way to counteract Chinese biological agents. It was determined that the way to achieve this was to alter the subject's DNA to cause immunity. During testing of PVP in 2076, abnormal side effects were observed in test subjects. The test animals began to grow dramatically and their brain activity increased. Seeing the potential there, the Army sent its own people to secure the project and renamed it FEV: Forced Evolutionary Virus. Not content with mere immunity to disease, FEV would turn soldiers into abnormally strong and intelligent supermen. When testing on animals reached its logical conclusion, the US military moved FEV research to the Mariposa Military Base where secret testing on human volunteers (read: military prison inmates) proceeded.

Great War
However, the grim nature of the research being carried out at Mariposa greatly unnerved the garrison guarding the base. The nature of the scientist's work, which had until then been a secret from the Army grunts, caused them to more or less revolt once they found out. Robert Spindel, the colonel in charge of the garrison lost his mind and committed suicide. His second in command, Captain Roger Maxson, took command of the troops and began interrogating the scientists. Rattled by the vile things the scientists were doing to test subjects and incredulous of the claim that the science team was only following orders, Maxson had the researchers executed one after the other. Later, he announced the Mariposa Military Base to be in full secession from the United States. Soon after, the bombs fell and the United States ceased to be. Disgusted with the Mariposa base, haunted by the test subjects and the executed scientists, Maxson decided to lead the troops and their families to the Lost Hills government bunker, where they would later use their high tech military equipment and knowledge to form the Brotherhood of Steel.

Grey's expedition
The Military Base was quiet for a long time. Not long after the war, however, a group of explorers, including Harold, entered the Military Base looking to end a peculiar proliferation of mutated animals which seemed to be coming from the base. The exact date of the expedition is unknown, but Harold's presence as a human being leads me to believe that it can't have been more than ten or twenty years after the bombs fell since Harold is known to have been a vault dweller who emerged shortly after the war's end. Thus, to still be alive and human, he'd have had to have entered the Military Base not long after the war.

Leading the expedition was Dr. Richard Grey, previously known as Richard Moreau until he was exiled from Vault City. When Grey's team entered the Military Base, most died when they encountered the automated defense systems (robots). Soon, only Grey and Harold remained. Harold was knocked out (he never did find out how) and woke up out in the desert looking like a ghoul. Grey, however, was headed for bigger trouble. He had made it to the vats room, where massive bubbling cauldrons of thick, green FEV waited to be experimented with. Grey was knocked into a vat by a crane and managed to crawl out. FEV was initially meant to be injected into humans, but Grey soon found out that direct physical contact worked as well. He began to mutate in horrible ways, turning into a sort of blobby kind of thing. He developed psychic powers, which were enhanced by consuming living minds to expand his own brainpower. Slowly, as wanderers made it into the base themselves, he started doing his own experiments with FEV.

The Master
Grey found that many of the test subjects were turning giant, mindless brutes with the brains of a child, if they survived at all. However, a rare few test subjects yielded super mutants. Immune to disease and radiation and blessed with exceptional strength, intelligence and endurance, super mutants were superior to humans in every way. They also possessed the exceptionally long life of the mutated as well as the total sterility. Grey--who now called himself the Master--lamented the needless destruction of the war. In his warped state, he decided that he would have to force humanity to evolve. If everyone could be as perfect as his super mutants, there would be no more conflict. Those who could not evolve would die. The Master began seeking out uncontaminated humans with which to create mutants and build his super mutant army.

However, creating super mutants was a very hit or miss process. The great majority of super mutants produced by the Master and later his Lieutenant in Mariposa's Vats were big, dumb brutes. Physically, there were vastly superior to humans, but they had the intelligence of children. What exactly causes some mutants to be brilliant and others to be stupid is unknown. The Master was certain it was related to radiation damage: humans who hadn't been exposed to much radiation yielded better mutants (see his personal diary for his thoughts on this). His Lieutenant, however, had a different theory. When the bombs hit the research facility and turned it into the Glow, they cracked open a few tanks filled with FEV. The bombs' radiation then mutated this FEV into an airborne strain. But this new airborne FEV didn't have any real mutagenic effects on people. All it did was inoculate human subjects against the real FEV, acting as a sort of vaccine. The ideal dipping subject was someone who hadn't been exposed to the airborne FEV. Both these conditions--no radiation exposure and no mutant FEV inoculation--were present in one population: Vault dwellers. Each one contained around 1,000 viable subjects to be dipped and turned into super mutants. Which factor exactly determines what you'll get from a dipping--radiation or inoculation--is still uncertain, though as a rule of thumb, the cleaner the subject, the better.

In 2162, a man known as the Vault Dweller managed to kill the Master in his Cathedral and destroy the Vats, and the Mariposa base collapsed.

The Enclave
In 2236, the Enclave excavated the Mariposa Military Base, largely using slave labor gathered from the nearby mining town of Redding, eventually finding the Vats deep inside the lower levels of the base. Though they had been buried in rock and forgotten for decades, the Vats still contained that old familiar green bubbling gunk, Forced Evolutionary Virus. The Enclave gathered samples to be sent back to the Oil Rig for further analysis. Before long, though, the slave miners, some being fully exposed to raw FEV, others likely falling into the Vats accidentally, began to mutate into a second generation of super mutants. The mutant slaves soon overthrew their guards. Seizing their weapons, hardware left behind by the first Mutant Army or anything lying around, the super mutants stormed the upper levels and quickly overran the troops in the base. Panicked and retreating, the Enclave troopers on the upper levels fled the base and used explosives to seal the entrance, trapping the second generation mutants inside the base.

Still, even though things went badly at Mariposa, the Enclave still had the samples of FEV they needed. Back at the Oil Rig, the United States Chemical Corps began work on the serum immediately. They found that it would be possible to make from FEV an incredibly potent and lethal toxin. But, in order for research to progress, they would need test subjects. They needed two test groups: one of clean, pure humans and another composed of the 'mutants' that lived all over the mainland, suffering radiation and FEV exposure for decades that, to the Enclave, made them unclean. The unclean sample was easily obtained by kidnapping the entire population of Arroyo: who would notice if one isolated Tribal village disappeared overnight? Most civilized people in the wastes hated Tribals anyways.

The clean group would be more difficult, though. The Enclave wouldn't allow the Chemical Corps to use people living on the Oil Rig (presumably because they were all too important to the Enclave's various projects). So, they had to look elsewhere. Once again, the mainland provided the needed stock. Thanks to the Vault Experiment project, they were able to see that the population of Vault 13 was largely intact. Thus, they travelled in force to Vault 13 and sent a command to the Vault's computers to open the Vault door. After taking care of some mild resistance, the Enclave troops rounded up the residents of Vault 13 and shipped them off to the Oil Rig in vertibirds to take part in the Chemical Corps' FEV experiments.

Before long, the Chemical Corps developed their supertoxin. It was found to be 100% lethal to tainted humans. Just as the Enclave was preparing to launch the poison into the jet stream to kill the entire population of the mainland, the Chosen One arrived at the Oil Rig on the Poseidon Oil tanker that had sat in San Francisco for years. He freed the survivors of both the Vault 13 population as well as the Arroyo tribals and started a self destruct sequence in the Oil Rig that destroyed the entirety of the Enclave's headquarters, saving the world from horrible death at the hands of the mutant FEV.

Appearances in games
FEV appears in some form in all Fallout games.