Breed to Come — Andre Norton

When desperate measures failed to control what men had begun and could not stop, they fled their polluted planet, leaving behind an epidemic virus born of experimentation. Yet unlike men, whom the disease could destroy, the animals of the planet thrived, each generation more forceful and intelligent than the last.

In the ruins of what was once a university complex a vast band of cats, more highly evolved than those on the outside, sought to master the works of man. And they learned that the Demons--as men were called--were not legendary, but real. Then one day a spaceship landed ...