Whether a woof, ruff, yip, or yap, dogs bark dozens, if not hundreds, of times each day. Imagine if every pet canine in the U.S. -- all 83.3 million of them -- congregated. The chorus would be a postal worker's nightmare.
Dogs sound off in almost any situation. Maybe the doorbell rang, or a stranger approached, or a bird fluttered nearby. Even with little to no obvious stimulation, dogs can bark incessantly. Behaviorist and biologist Raymond Coppinger once observed a dog that barked for seven hours straight, even though no other canines were within miles.
Because dogs bark repetitively and in varying contexts, for decades, a hefty chunk of scientists argued that these sounds served no specific purpose. Coppinger, for example, put forth the notion that barking relieves arousal, and merely indicates an emotional state. At the turn of the century, however, these views started to evaporate. A key clue came in 2002. UC-Davis animal scientist Sophia Yin recorded the barks of different breeds of dogs at play, when the doorbell rang, or in isolation. She found that bark frequency and duration differed significantly between the situations.
"The fact that barks were context specific... strongly suggests that barks serve specific functions," she reasoned.
For all the barking the dogs do, their closest relatives, wolves, rarely bark at all. As little as 2.3% of their vocalizations are barks; the rest are almost entirely howls. Moreover, wolves bark only in warning, defense, and protest. Even though 30,000 years of evolution separate the two species, many breeds of dogs look quite similar to their lupine cousins. But the sounds they make are easily discernible.
Taking note of this contrast, Hungarian ethologist Csaba Molnar forayed into the barking discussion, postulating that the bark came to prominence through the process of domestication, in essence, as a way to communicate with humans.
In 2005, Molnar presented evidence to back his assertion. Molnar had 36 subjects listen to a variety of barks from a breed called mudis. The barks were recorded during different situations: when the mudis encountered a stranger, acted aggressively, were prompted to go on a walk, begged for a ball, played, or were left alone. Regardless of whether or not the subjects were dog owners, they were able to guess the situations in which the barks were recorded at levels significantly higher than chance when presented with the choices.
Further evidence backing Molnar's theory came courtesy of Dmitry Belyaev's domestication experiments on silver foxes. For years, researchers selected the most docile foxes that showed the least fear of humans and bred them. Over the generations, the foxes began to sport characteristics like spotted coats, floppy ears, and curled tails. They also began barking a lot more, specifically when they saw people!
It might be presumptuous to think that barking evolved on our account, but right now, it's the most plausible explanation we have!