In this world, there are basic animals, much like in our own. Cats and dogs and the like. Over millions of years, evolution took the lead, and many of these creatures evolved, growing smarter and larger. Over time, they learned to use tools, and how to share their knowledge, helping each other to grow as a civilization, until they reached the modern day world they have now. These evolved creatures also kept much of their fur, claws, fangs, and the like, finding them useful to surviving the harsh environments that they roamed, a fact that also allowed them to focus on other things, pushing some elements of their prehistoric civilizations forwards

Humans were another species that evolved, an offshoot of primitive monkeys, it seemed, but one that never reached to the levels of their Furred, Scaled, and otherwise, counterparts. They weren't stupid, though, growing more intelligent alongside civilization. Throughout history they had been useful, from labor to playthings, and eventually, when they became far less necessary for handling simple tasks throughout the world, as pets. Smart and able to learn plenty of tricks, they were quite valuable, and given that they were all quite similar, to a certain degree, it caused them to be easily adaptable to the owner that chose them. I'd liken them to crows, and other intelligent animals of our world. Able to use tools and figure things out, but clearly not as evolved as we are.

As time went on, these humans became quite common pets, often found in many a household. Of course, like with us with our own animals, as well as with AI, many wondered if they could be more. Tests occurred in the world, people wondering if humans could be made smarter, or if they were simply stuck at the levels they were now, unchanging for at least a few hundred years.

Then one day, everything changed.

A lab had been working on a sort of drug that could be used to greatly amplify human minds, super-charging them, to at least get them to a level similar to that of their owners, if a little below. One thing they hadn't planned for was for their creation to somehow get loose, airborne, and as infectious as it became. Soon enough, humans the world over were starting to speak, doing things they'd never done before, a whole new intelligence lodged in their heads! Many hurt themselves in this new time. After all, they'd been animals only days before, and now they were being filled with a whole new selection of thoughts and ideas!

From then onward, humans were greatly examined and experimented with, scientists of all kinds, across the globe, trying to figure out to what degree this intelligence would grow, how it would affect the humans that it had spread too, which was a massive reach. Humans, of course, didn't really understand what was going on. They had a deeply instilled sense of purpose with their owners, or hopefully-soon-to-be-their-owners, and so they clung to that in this time of confusion and worry.

After a few years, though, Humans were deemed to be safe to the population. They weren't infectious any longer, and their intelligence didn't seem to be morphing into anything else just yet, and on top of it all, their being able to communicate and understand was only going to make them all the more useful and helpful across the world. In the end, owners continued to own their pets, but had a newfound sense of companionship with them. They cared for them, still seeing them as their loving pets, even if they could hold a conversation.

Humans too seemed happy with their arrangements. While they knew they were not equals to their owners in the eyes of the law, or even much of the population, they felt that same deep-seated love. An existence-worth's training and caring was hard to get rid of in even a few years, and so they put their minds into what they'd always done, trying to help make the world better for those they loved, and getting plenty of treats and rubs in return!

My setting takes place some time after the intelligence boost, in a time where humans have begun to learn more and more, but are still loved as, and taken care of as, pets. They are still under observation, as any rapidly-evolved species would be, but their presence is an accepted fact of the world.

tl;dr: Furries rule the world, accidentally give humans intelligence, but humans, much like dogs, have love so ingrained into their beings that they use said intelligence to just keep doing what they'd been doing, all while being more helpful.