In 1973, something occurred that even science couldn't explain. Some humans were born with two sets of DNA. One set was human DNA and the other was that of an animal. Known as "hybrids", these people were seen as an imbalance to ecosystems. They were tolerated by the world for quite a while. In 1998, certain hybrids began to attack other humans. Therefore, it was decided that these people were contained by their governments to protect humanity and other organisms around the world.