Fallout: The Forced Evolutionary Virus (FEV) Explained

"Much of Fallout's many creatures roaming the wastes have not occurred naturally. From fire ants, to super mutants and intelligent Deathclaws, there is a single artificial virus to thank for many of the creatures in the wasteland: The Forced Evolutionary Virus, or FEV for short. Different organizations have used and adapted it for different agendas both before and after the Great War." - click image for article