A/N: Hey guys! Hope you guys like this story. As per normal, R&R. Enjoy!
The Flare. An evolved virus to… control the population. The world was overpopulated and this was the only solution. Survivors who contracted it would go insane and feral. As the bodies piled on in the millions, the authorities realised that they had made a mistake. It was spreading too fast. As humanity dwindled down into a hot stinking mess, the lucky few millions who were immune hid beneath the ground, waiting it for it to die out. All of humanity's achievements were gone in the dust. Naturally, some were prepared for this scenario and had underground bunkers to house scientists, mechanics, engineers… fixing any problems these vaults might have.
(100 years later)
It was unbelieving. Somehow, the Flare had transformed into an evolutionary virus, its code rewritten by the scientists and Mother Nature. It sped up evolution. Naturally, to study further upon the virus, there were copies of it in its original form, under lock and key in a hidden laboratory. It had fingerprint security, heat detectors, foot sensors, retina scanners, fingerprint scanners, all the technological goodies from the past.
With ethics thrown out of the window, they tested the virus on innocent animals such as rabbits, hares, foxes, anything they chanced upon. This of course was intended to aid humans in being evolving to be immune to any other future strains of 'The Flare'. However, their 'testing' had produced some unintended results. The virus had caused the animals' cortex to expand significantly, with some rabbits shakily standing on their hind legs.
(Five decades on)
There had been no doubt by the scientists that their predecessors had created something quite amazing. Animals were gaining a conscious and spy links reported the animals beginning to build structures similar to those in the Bronze Age. Premature Agriculture methods had been developed by the animals and a basic form of language had been established. Interestingly, these animals had decided to name their town 'Zootopia', perhaps influenced by the animal enclosures their forebears had been held captive in.
It had been 150 years since the Flare, and humans had adapted to the underground environment due to the enhanced Flare virus. With their agriculture, technological and social problems solved, humanity turned to the next big thing. What was humanity going to do with the evolved animals?
After much consideration and debate within the Confederation of Humans, their new government, it was decided that humanity would be a bystander and let the animals evolve. The engineers then embarked on setting up cameras and the electrical wiring to keep a close eye on the animals.
Of course, the humans wanted it easier to keep track. Thus, there happened to be dictionaries and thesauruses left around the slightly more advanced animal city, which now had buildings resembling Victorian architecture. The animals had not really thought about why the books were there, they just followed along and set up a language extremely similar to 21th century English. Humanity quietly watched as Ludwig Van Barkthoven, a dog, play a glorious masterpiece on an animal version of Fur Elise on the piano, with certain modifications such as staccato pedals and so on. They watched the many parallels to human society and decided to be more proactive by helping them avoid human mistakes like pollution. Some of the eco-friendly generators and fuel were placed in the city for the animals to develop and use.
It was incredible what had happened. A sheep had chanced upon a flower which contained the old version of the Flare and farmed it for her grand scheme: Turning all predators into savages and then promote species hegemony for prey. Thankfully, the situation had been controlled through a brave bunny and a charming fox known as Judy Hopps and Nick Wilde respectively. It was a close call, but the shipment of plants labelled explicitly as 'Night Howlers' (the animals' name for that plants) with a list its effects had probably helped the bunny identify the true culprit. With this cosmopolitian city saved, humanity embarked on colonising other planets to bring more resources. Thus, they left their home planet for other planets, leaving a small crew of one thousand dedicated scientists to control the situation.
The 'Night Howlers' were placed into a large warehouse, along with the antidote and some other serums (which cured some animal sicknesses). After its construction, most of humanity promptly left the planet so as to not drain the planet's resources further.