The gods have grown tired of the human race they were arrogant, greedy, obnoxious and violent. the gods thought a change was in order something else to replace humanity.
After some discussion the gods decided that the new species (whatever it would be) would act like a virus that would change not just the human race but other races and the world itself once the virus has transformed the whole world it will be nothing like it was.
All that was left was to choose how the virus would change the world and who the human would be to host the virus in the end they came to a decision they would choose you to be the host of the virus and the virus will transform the world into......