After thousands of years of cohabiting with domesticated dogs, it’s surprising to think that we still don’t fully understand why our furry companions wag their tails. Hoping to finally crack this canine conundrum, the authors of a new opinion piece speculate that the behavior may have arisen to satisfy humans’ intrinsic sense of rhythm.
While it’s commonly believed that dogs wag their tails when they’re happy, the scientific literature doesn’t always back this up. For instance, after reviewing more than 100 studies, the authors uncovered evidence to suggest that aggressive dogs wag their tails more than docile dogs – “a result that is counterintuitive to the widely held human belief linking tail wagging to positive valence in dogs.”
Other studies included in the review found that dogs wag their tails when presented with random objects such as fans and plastic bags, “with tail wagging in these situations thought to indicate positive emotions and/or high arousal, but not fear or stress.” On other occasions, pet pooches were observed wagging when they wanted to be fed, suggesting that the behavior could also function as a request signal.
Faced with such varied and contradictory data on tail wagging, the study authors are ultimately unable to draw any definitive conclusions as to why dogs shake their booties so readily. However, they do propose two hypotheses, neither of which have been tested but both of which carry some logic.
The first of these is known as the “domestication syndrome” hypothesis, and states tail-wagging may have emerged as an unintended by-product of human selection for other traits. To back this up, the researchers point to a study carried out on silver foxes, which were bred to become increasingly tame and docile over 40 generations.
“Although tail wagging behavior was not directly selected for, tamed foxes showed dog-like tail wagging behavior and had more curled tails,” write the authors. “This could have been due to a genetic link between the selection for tameness and tail anatomy,” they continue, all of which hints at a possible accidental link between friendliness and more waggly tails in domesticated dogs.
“Alternatively, tail wagging behavior may have been one target of the domestication process, with humans (un)consciously selecting for dogs who wagged their tails more often, and potentially more rhythmically,” say the researchers. “We call this the ‘domesticated rhythmic wagging’ hypothesis.”
Though highly speculative and unproven, this theory is based on cognitive neuroscience research which indicates that human brains have a natural preference for rhythmic stimuli. “This propensity for isochronous rhythms could have driven human selection for the conspicuous rhythmic wagging of the tail in dogs, and could explain why dogs exhibit it so often in human-dog interactions,” conclude the researchers.
Acknowledging the tentative nature of their proposals, the authors conclude that neither of these hypotheses is currently supported by robust evidence. They therefore call for more detailed studies to track the movement of dogs’ tails in different situations and monitor the brain activity associated with tail wagging.
The opinion piece is published in the journal Biology Letters.