My wife has just brought back an ornamental manx cat. That's the breed that doesn't have a tail. They originated on the Isle of Man about 300 years ago when a cat was born with the genetic abnormality of having no tail. This can happen in other breeds of cat, but because Man is isolated from the mainland, the mutation was able to flourish. It is an example of a macromutation, where a single change in the genetic code has a significant effect on the phenotype, ie. the non-appearance of the caudal vertebrae.
And when has this happened before? The characteristic that separates apes from monkeys is this same lack of a tail. Could the very first ape, the ancestor of gibbons, orang-utans, gorillas, chimpanzees, bonobos and humans, have been the offspring of a monkey that was born with a mutant gene for taillessness? Or was tail loss the result of incremental shortening over many generations?
I have never seen this issue addressed in any of the books on human origins that I have read, yet the absence of a tail was an important prerequisite to our upright stance. If anyone out there can give me answers, I would be most pleased if you would let me know.