Actually the Protestant Reformation might be a good time. It wouldn't be a scientific theory though this early, just a basic idea.
Say one of the priests who defects to the Protestants had, prior to doing so, travelled some distance, going throughout the Catholic world for Church purposes and venturing even farther to convert some pagans to Christianity. By chance at one of the larger cities he goes to he finds a wealthy merchant's entourage with exotic animals from Africa or the East. Many of the animals look like strange, giant versions of the ones he's seen--a lion, cheetah or tiger with a cat, a hyrax with a rat, a crocodile with a giant lizard, a jackal with a dog, and a monkey that looks like a tiny man.
He spreads the idea that God forged animals from other animals when he joins with a more prominent Protestant reformer. He might say that apes were made after man, or were men punished for being pagan, and made into tiny furry animals.
Two or three centuries later an actual theory of evolution is formulated with a more connected world with easier travel.