The real reason why dogs wag their tails

The mystery of why dogs wag their tail so much has long fascinated humans. Now, scientists think it might be because their owners enjoy the rhythm of the movement.

The bond between man and dog is unique in the animal kingdom with a symbiotic relationship allowing both species to flourish and humans exert significant influence on the appearance, temperament and behaviour of their pets.

A team of animal experts, including from the Max Planck Institute for psycholinguistics and the University of Rome, looked at the existing research on tail-wagging and found dogs do it much more than other canines, such as wolves.

They suggest this could be down to two reasons, either tail-wagging is an inadvertent side effect of humans breeding dogs that are tame and docile; or humans have deliberately bred dogs that wag their tails because we find the rhythm of it soothing and enjoyable.

The suggestions are just theories, but they are the first to try to understand the evolutionary purpose of wagging. Specialised research into the movement is needed to understand it better, the academics say.

In the wild, the tail has a practical function as it helps swat away pests as well as improving balance, but dogs wag their tail far more than other species to which they are closely related.

Domestication likely drove the increase in wagging prevalence, scientists say, and humans have been trying to tame dogs for more than 30,000 years.

But it remains unknown if wagging is the result of deliberate actions or a coincidence.

“Changes in tail-wagging behaviour could have arisen as a by-product of a selection for another trait, such as tameness or friendliness toward humans,” the researchers write in their paper, published in Biology Letters.

They point out that a study on 40 foxes, from 1999, found that when 40 generations were bred like dogs, selecting for tameness and other domesticate traits, foxes ended up behaving in a very dog-like manner, including more wagging than their ancestors ever did.

This suggests the genes associated with being friendly could also be linked to increased tail wagging.

It is also possible that tail wagging was not an unintended consequence of domestication, but a central goal, the team says.

Rhythm method

“Tail-wagging behaviour 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. We call this the ‘domesticated rhythmic wagging’ hypothesis,” they write.

Humans are good at picking up rhythms, the scientists explain, and they can trigger parts of the brain related to pleasure and enjoyment.

“Propensity for 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,” the scientists say.

Both theories explain why some breeds are more exuberant waggers than others, the researchers say.

“Under both hypotheses, selection on tail-wagging behaviour may not have been uniform across breeds; for example, hunting-type dogs wag their tails more than shepherd-type dogs, and have also experienced different selective pressures throughout domestication,” they say.

The team believe animal researchers have neglected researching the science of wagging and more work should be done to unpick its true meaning, origin and purpose.

“Targeted tail-wagging research can be a window into both canine ethology and the evolutionary history of characteristic human traits, such as our ability to perceive and produce rhythmic behaviours,” they say.

They would like to see scientists investigating all aspects of wagging, including if it changes as a dog ages, how much of the tail is actually under control, does a dog innately know how to wag or does it learn the skill, and how big a part do genetics play in wagging.