Joan Acocella at The New Yorker:
Writers aiming to tell us about human life have often done so under cover of telling us about animals. Animals are fun—they have feathers and fangs, they live in trees and holes—and they seem to us simpler than we are, so that, by using them, we can make our points cleaner and faster. With Madame Bovary, you pretty much have to say who her parents were. With SpongeBob, you don’t, and this keeps the story moving. Most important, the use of animals to stand in for human beings creates a fertile ambiguity. We know that the author is not proposing a one-for-one equivalence between human and nonhuman life, but some kinship is certainly being suggested. Think of Swift’s Houyhnhnms, trotting down the road, their withers shining in the sun, saying sober, passionless things to Gulliver. How beautiful they are, and how creepy. Animal narratives have allowed writers with lessons on their mind to make art rather than just lessons.
Such tales are no doubt as old as animal paintings on cave walls. The earliest evidence we have of them is the beast fable, a form that is said to have come down to us by way of Aesop, a Greek storyteller who was born a slave in the sixth century B.C. Actually, no solid evidence exists that there ever was an Aesop, any more than there was a Homer. As with the Iliad and the Odyssey, we are talking about manuscripts that date from a period much later than the supposed author’s, and were probably assembled from a number of different fragments.