Nothing gives a dog lover more satisfaction than coming home and being greeted by your four-legged friend furiously wagging his tail. Have you ever wondered how this common behavior arises, and why our species seems to appreciate it so much? This was done by a group of researchers from the University of Turin, the University of Vienna and Nijmegen, coordinated by the psychologist Andrea Ravignani, of the Sapienza University of Rome, investigating the scientific literature available on the physical mechanisms that guide the tail wagging of dogs, and on the development and evolution of this complex social behavior. Their findings were recently published in the journal Biology Letters.
First, it is important to remember the origin of our domestic dogs. As far as science knows, the long process that transformed ancient wild wolves into dogs began about 35,000 years ago. Our ancestors began to collaborate with wild canids, hosting them in their camps and guiding their reproduction through a process of domestication, which generated a long series of physiological, morphological and behavioral changes from which modern domestic dogs originated.
Is the propensity to wag one of them? Almost certainly yes: wolves show this behavior much less often than dogs, and the few times they do, especially as adults, it is within ritual behaviors that serve to cement the balance of power between dominant and subordinate specimens. Dogs, on the other hand, wag their tails in a multitude of situations, in moments of joy, but also in interactions with other dogs and humans. Something in the myriad of changes that occurred during the domestication process of dogs must therefore have changed the way they wag their tails.
Direct or indirect selection
From the analysis carried out in the new study it emerged that there are essentially two types of hypotheses that have tried to explain the appearance of the new traits that emerged in dogs following the domestication process: they can be the by-product of the selection that took place for other characteristics, or the result of direct genetic selection operated by man. Examples can help you understand the difference. In the first case, life alongside our species may have made it advantageous for dogs to possess characteristics such as docility, playfulness, or a marked sociability. If for some reason animals that possess these characteristics also have a greater propensity to wag their tails, over the course of thousands of years wild wolves become domestic dogs, docile, playful and sociable, and ready to wag their tails at the first opportunity.
In the second case, however, tail wagging would be the trait on which selection acted: if our ancestors had found, for any reason, the tail wagging of dogs pleasant or useful, they would probably have started to prefer the one that did it more often, giving it greater opportunities to survive and reproduce (if not directly selecting this phenotypic trait as modern breeders do) and therefore pushing evolution to endow the entire species with a strong propensity for tail wagging. How are things really? It’s hard to say, but researchers have gathered some evidence in favor of both explanations.
Experiments and neuroscience
The first of the two explanations is in fact in line with the results of a long-term experiment that sought to replicate the process of domestication of mammals and to follow the changes it induces in the behavior, genetics and development of these animals. The experiment was conducted on silver foxes (Vulpes vulpes), which have been bred for 40 generations and directly selected for tamability and docility. At the end of the research, the resulting population of foxes exhibited behavioral, physiological and morphological traits similar to those observed in dogs. And although tail-wagging behavior wasn’t directly selected for, the domesticated foxes ended up wagging their tails much like dogs, and had curlier tails than their wild ancestors. This would support the hypothesis that the domestication process may have indirectly modified dog tail wagging, making it a more common behavior than it is in non-domesticated canids.
In support of the second hypothesis, however, the researchers cite the possibility that the rhythmic movement of dogs’ tails is something intrinsically pleasant for our species. This possibility would be corroborated by several multidisciplinary clues, which indicate that humans have remarkable abilities to perceive and produce rhythmic sequences, in particular periodic patterns in which events are uniformly spaced in time. Although it is not clear how this behavioral characteristic appeared in humans, cognitive neuroscience has shown that the human brain prefers rhythmic stimuli, which trigger pleasant responses and involve brain networks that are part of the reward system. This propensity may have driven human selection for conspicuous rhythmic tail wagging in dogs and may explain why dogs display it so often in interactions with our species.
In short, the possibilities are still all on the table for now. For this reason, researchers believe that the study of dog tail wagging is a field that deserves further study in the future. Investigations that could provide important insights not only on the evolution of our four-legged friends, but also on that of our species. “The combination of techniques of behavioral analysis, computer vision and physiology with neuroscience will be able to help in the future to distinguish between tail movements under control, therefore under possible selection, from those deriving from mere mechanical effects such as, for example, the tip of the tail which would move as a consequence of the fact that several cranial portions of the tail have been subjected to a selection action”, explains Ravignani. “A more systematic and in-depth investigation into tail wagging will not only allow us to better map this iconic dog behavioral manifestation, but will also provide indirect insights into the evolution of human traits, such as the perception and production of rhythmic stimuli.”