The longer the post, the less likely it will be read. And, if read, the less likely it will be understandable.
I think the story is an analogy of human-kind's moral evolution. How people treat each other as the general level of intelegence grows.
In the beginning the cat & rats were non-sentient animals. They had no morals and would fight with, steal from, or kill each other without any guilt.
As their intelligence and knowledge grows, their treatment of one-another and other animals changes (rats don't eat each other or fight, cat doesn't kill talking rats, etc...). Eventually, the rats treat each other more "humanely" than the humans do (who are kind of backwards and dumb, and therefore less moral)!