An Unnatural Sound
Wolves, from which dogs are descended, do not bark with the same continuous, explosive, non-stop stream of noise we get from today's dogs. In his book,
Dogwatching (Crown Publishers), Desmond Morris describes the barking of the wolf as being "modest and abbreviated." He says, "Wolf barking is not particularly loud, or particularly common, and is always monosyllabic. It is best described as a staccato 'wuff' sound. It is usually repeated a number of times, but it never develops into the noisy machine-gun fire so typical of the wolf's domestic descendants." In other words, dogs bark louder, longer, more frequently and in a more percussive manner than the animals from which they are descended.
The explosive and persistent bark of the modern dog, then, is not an abomination of nature. It is an abomination of man. For some reason, some of our ancestors thought that when it came to barking, more is better.
So across the millennia, some of those who came before us bred dogs in a selective manner to create today's modern bark of excessive dimensions. You can see then that the barking we hear today is not truly a natural sound. As Morris says, the voice of the modern dog is the result of "ten thousand years of selective breeding" to produce the "superbarker" we have today.