Why do dogs tilt their heads? New study offers clues
Or maybe they to it because <i>we</i> think it is cute.  The dog's evolution is totally tied to their interactions with humans.  The head tilt is a form of communication, them telling us that they are doing a particular behavior.  Those that head tilt would better communicate with people, resulting in better treatment, more breading opportunities and an evolutionary pressure towards more head tilting.<p>These are border collies, a working dog designed to interact with a human handler.  Take a look at something like a cane corso or great pyrenees.  They don't head tilt nearly as much because such close communication is not what we have, through breeding, designed them to do.