Is Dog Barking the Result of Human Artificial Selection?
The Basenji also called the Congo Terrier is native to the Central African forest. Since ages he is used by the pygmies (thought to be the oldest of all humans) to hunt lions. Therefore the basenji is one of the oldest breeds of dogs. He does not bark, but he can make all the same noises that a wolf or coyote can make. He can scream, cry, howl, whine and growl.
The Can't Bark-Hypothesis
Why this breed doesn't bark remains a mystery. Some believe it's due to an anatomical difference in the larynx, the part of the throat that houses the vocal cords. The lateral laryngeal saccules are absent or reduced and the laryngeal recesses (ventricles of Morgagni) are shallow compared with those of other dogs . This led some people to assume that because the vocal fold is restricted on its lateral side it limits the vibrations of the vocal fold and therefore the ability to bark. No other significant differences were discovered. It is not yet established whether or not these anatomical features are directly related to barklessness in basenjis.
The Don't Want to Bark-Hypothesis
Others believe that Basenjis can bark but just don't want: Basenjis might have been trained by people not to bark many thousand years ago, and this characteristic was passed down throughout future generations of the breed. Scott and Fuller did a thorough study of barking behavior, comparing basenjis, beagles, shelties, cockers and wirehaired fox terriers . Obviously, basenjis are not completely barkless. When sufficiently excited, they will bark:
Basenjis barked during 20 per cent of the opportunities given them during the dominance test, whereas the cocker spaniels barked during 68 per cent. The basenjis usually gave only one or two low “woofs” when they did bark, the average number being about two. At 11 weeks of age, the largest number of barks given by any basenjis during the dominance test was 20 and the next highest number was 12. More than this, the sound which the basenjis make has a different quality from that in other breeds. Thus there are three different aspects of what looks offhand to be a simple behavior trait. One is the threshold of stimulation – very high in the basenji and very low in the cocker spaniel. A second trait is the tendency to bark only a small number of times rather than to become excited and bark continuously as do many cocker spaniels.
Through experimental breeding between basenjis and cocker spaniels, Scott and Fuller determined that the trait of being easily stimulated to bark is probably controlled by a single dominant inherited gene. Their opinion seems to be that it is the high threshold of stimulation that makes basenjis barkless. In other words, they can bark but don’t, at least not very often.
Dog Barking is a Neotenic Trait
An evolutionary biologist takes the basenji as the exception from the rule and asks why dogs bark at all because wild dogs yip and squeal and whine, but rarely produce the repetitive acoustic percussion that is barking. Darwin was also fascinated with the novel quality of dog barking because according to his opinion it has no obvious precedent among wild wolves.
The habit of barking, however, which is almost universal with domesticated dogs, forms an exception, as it does not characterize a single natural species of the family.
[The Expression of Emotions in Men and Animals] p 27
All modern observers of wolves under any conditions, whether in zoos or in the remote wilderness, agree that they bark, although not as much as many dog breeds. In wolves, from which modern dog breeds are descended, barking is done mostly by pups. Thus dog barking is neotenic — something derived from a juvenile stage, and kept in adults. It comes about because of delays in development. In such cases, a species’ neotenous form becomes its “normal” mature form, no longer dependent upon environmental triggers to inhibit maturity. The mechanism for this could be a mutation in or interactions between genes involved in maturation, changing their function to impede this process.
The Evidence for Human Artificial Selection
Up to today No one knows how barking evolved, except to observe it arose during 50,000 years of domestication. “The direct or indirect human artificial selection process made the dog bark as we know,” said Csaba Molnar, formerly an ethologist at Hungary’s Eotvos Lorand University.
Molnar reasoned that if this hypothesis were correct, two facts would need to be true: First, dog barks should be acoustically different, and humans should react to dog barks as communicative signals—that is, they should be able to judge the emotional state of the dog and/or the situation in which the bark was emitted.
Compared to the other vocalisations (like growling, howling, whining, etc.) of wild canids, dog barks are highly variable and it has been found that dogs emit acoustically different barks in different situations suggesting that motivational changes in the dog are reflected in barking vocalisations.
In a paper published in the Journal of Comparative psychology , Molnar compared the acoustic structure of dog barks recorded in different behavioral situations and allowed humans to categorize these dog barks and describe their emotional content. Human listeners had to choose one of six possible situations (stranger appears, dog attacks human, left alone, before walking, asking for ball and playing with humans) after they listened to a bark sample. Similarly, they had to rate the possible emotional state of every bark sample on the basis of five emotional scales (aggression, fear, despair, happiness and playfulness). Further, he looked at the role of experience by choosing humans with different experiences of dogs for the playback experiment. Listeners were able to categorize bark situations high above chance level. Emotionality ratings for particular bark samples correlated with peak and fundamental frequency and interbark intervals.
In a follow-up study he looked at the acoustic parameters of dog barks which carry emotional information for humans . The scoring of the emotional content of the bark sequences was in accordance with the so-called Morton’s structural–acoustic rules. Thus, low pitched barks were described as aggressive, and tonal and high pitched barks were scored as either fearful or desperate, but always without aggressiveness. In general, tonality of the bark sequence had much less effect than the pitch of the sounds. He found also that the inter-bark intervals had a strong effect on the emotionality of dog barks for the human listeners: bark sequences with short inter-bark intervals were scored as aggressive, but bark sequences with longer inter-bark intervals were scored with low values of aggression. High pitched bark sequences with long inter-bark intervals were considered happy and playful, independently from their tonality. The authors found almost no effect of previous experience with the given dog breed or of owning a dog.
In another research paper Molnar used a machine-learning algorithm to classify dog barks . A pool containing more than 6,000 barks, which were recorded in six different communicative situations was used as the sound sample. The algorithm’s task was to learn which acoustic features of the barks, which were recorded in different contexts and from different individuals, could be distinguished from another. The program conducted this task by analyzing barks emitted in previously identified contexts by identified dogs.
The algorithm showed that dog barks displayed common patterns of acoustic structure. In terms of pitch and repetition and harmonics, one dog’s alarm bark fundamentally resembled another dog’s alarm bark, and so on.Intriguingly, the algorithm showed the most between-individual variation in barks made by dogs at play. According to Molnar, this is a hint of human pressure at work. People traditionally needed to identify alarm sounds quickly, but sounds of play were relatively unimportant. The findings support Molnar’s original hypothesis, though more work is needed. The ultimate evidence, said Molnar, would be if human knowledge of bark structure could be used to synthesize barks. “If these barks, played to dogs and humans, had the same effects, it would be awesome,” he said.
 Pongrácz P, Molnár Cs, Miklósi Á & Csányi V (2005) Human Listeners Are Able to Classify Dog (Canis familiaris) Barks Recorded in Different Situations Journal of Comparative Psychology, 2005, 119, 136-144.
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