WHY DO DOGS WAG THEIR TAILS?

Have you ever wondered why dogs wag their tails?  The answer is remarkably simple: the sole purpose of this act is to communicate with humans.  Dogs (you may have noticed) cannot talk.  They therefore use the only method of communication (other than primitive vocal sounds like growling) they have to express their feelings as clearly as possible.  Dogs in the wild wag not.  It is done entirely with humans in view.