Whether it is an elegant swish or a furious oscillation, tail wagging is ubiquitous among dogs. Now researchers have suggested it may have become commonplace during canine domestication because humans love its rhythm.
It is thought humans domesticated dogs sometime between 15,000 and 50,000 years ago – a process that has led to a fervent bond between the two species, with about a third of households in the UK having a dog.
But while owners often rely on tail wagging to interpret how their dog might be feeling, it remains unclear just how such canine semaphore evolved.
Now experts have outlined a number of theories in an attempt to encourage researchers to dig into the issue.
“We may not be able to take a time machine back to the beginning of the dog-human relationship, but we can look at dog behaviour today in tandem with human behaviour to try and understand what that domestication process looked like,” said Dr Taylor Hersh, a co-author of the article, from Max Planck Institute for Psycholinguistics in the Netherlands.
“Tail wagging is a very apparent and interesting behaviour to start with.”
Writing in the journal Biology Letters, Hersh and colleagues describe a number of studies that have previously looked at tail wagging.
Among them, experts found hand-reared dog pups wag their tails far more often than hand-reared wolf pups, and that dogs wag to their right in response to positive experiences – such as seeing their owners – and to their left when they wish to withdraw, for example in aggressive situations.
However, questions remain, including why dogs wag their tails more often and in more contexts than other canines.
One possible trigger, the team say, is the domestication process, with research previously suggesting other traits in dogs arose because they have a genetic link to behaviours humans selected for – such as tameness or docility. Hersh and colleagues say something similar could be at play for tail wagging.
But, they suggest, there could be another explanation.
“We put forth a new hypothesis that humans consciously or unconsciously selected for tail wagging during the domestication process because we are very attracted to rhythmic stimuli,” said Silvia Leonetti, first author of the article.
The team are now calling for new investigations into tail wagging to investigate the possibilities, with Leonetti adding that experiments using advanced and non-invasive technologies – focusing not only on single dogs but on dog-dog and dog-human interactions – could help to shed further light on the action’s various meanings.
While the article has been welcomed by others, Dr Juliane Bräuer of the Max Planck Institute for Geoanthropology noted it was possible heightened tail-wagging was directly selected for by humans for reasons other than its rhythmic nature.
Dr Holly Root-Gutteridge, a dog researcher at the University of Lincoln, said in her view tail wagging was a social signal between individuals that dogs had adapted to use with humans because people found barking irritating.
“We’re a highly visual species and may appreciate the rhythm, it’s an interesting thought that should be explored, though I’m not sure we’re really responding that much to it,” she said.
Root-Gutteridge added wolves also wagged their tails, and used it as a social signal, although data was limited on its use in the wild.
“I suspect ancestral humans saw tail wags as a positive, easy to read sign in wolves, and developed it the way we talk with our hands – as a communicative gesture that we can easily understand.”
