Imagine human civilization at its peak. Ten billion people well fed, educated, given equal representation and universally equal rights. They can visit any state in the world for a half week's salary, choose any of a thousand artists from a thousand television stations, read books on any subject imaginible, pay for classes for any skill they want to pick up, and still be able to spend time with their children. People like you -- the altered ones -- were at that time created for vanity, for pleasure, for fashion, occasionally even for medical or theraputic reasons. However, it was not common -- why spend a year's worth of income when the newest Star Wars remake was about to come out?
Imagine this paradise, without need or want, dead in a day.
Four generations ago, the early 21st century, your ancestors were in the middle of a holy war. Technology being what it was, there was no other real reason to go to war. All of the great weapons were brought out to clean out the heretics. First, they used nukes. When they ran out of nukes, they used diseases. When they ran out of diseases, they used napalm and gas. When they ran out of gas, they sent their soldiers in. And about by this time, they had more nukes and napalm and mustard gas ready to go.
When the nukes rained down, it was hell. While patriotic messages blared out how we were winning (as no doubt the other sides were all doing), people looted, raped, and killed. The Federal Government was reduced to a few manned satellites and a NPR station operating out of Barrow, Alaska within a matter of days.
Nobody was prepared (or at least, prepared enough) for the reality of what was about to happen. Nobody was prepared for actual chaos. And that's when the utility of being half-human, half-animal became apparent. Fur kept the retrocodes warm on cold nights. Instincts showed them tactics for survival unmodified humans did not think of or could not stomach doing. And claws were better than fingernails in a fight...
It's now sometime in the early 22nd century. Survival of the fittest has had four generations to work, and humanity's long sunset is being overtaken by the rising moon of the furry race. There's a new world awaiting those who have the intestinal fortitude to rise up from the squalor and go take a chance.