Why do dogs wag their tails?

Understanding why dogs wag their tails is quite complex.

Dogs wag their tails when they are excited, happy to see you arriving home, when you pick up their leash or throw a stick. Or so it may seem to the average unsuspecting human.

Tails are common across vertebrates and originally evolved for locomotion, with many animals also using tails for balance and swatting pests. In dogs, tails are no longer primarily used for locomotion, but rather, are used for ritualised communication.

Dogs wag their tails more frequently and in more contexts than any other species in the Canidae family of dog-like carnivorans.

Wagging can vary by individual, sex and breed. For example, hunting-type dogs wag their tails more than shepherd-type dogs and have also experienced different selective pressures throughout domestication.

Differences in dog and wolf tail-wagging behaviour appear as early as three weeks of age, even when pups of both species have been raised in the same way.

Comparative studies between wolves and dogs have shown that the domestication process has shaped dogs’ cognition and sociability in both dog-dog and dog-human interactions.

The domestication process probably began around the Stone Age (approx. 35,000 years ago) and may have led to changes at the behavioural and anatomical level that altered tail-wagging behaviour in dogs, so domesticated dogs wag more often and in more contexts than non-domesticated canids.

In a famous long-term experiment in Russia, geneticists who domesticated silver foxes over generations found the domesticated foxes regularly wagged their tails and acted more like dogs than their wild counterparts.

This may have been due to a genetic link between the selection for tameness and tail anatomy. For instance, initial selections for docility may have triggered alterations of the neural crest cells during development, with repercussions on various phenotypic traits that include tail anatomy.

Interestingly, dogs show a sophisticated ability to communicate and cooperate with humans; in experimental tasks they efficiently perceive and respond to human communicative cues such as pointing and gaze.

Dogs frequently wag their tails when interacting with familiar and unfamiliar humans but wag the most when their owners are present. Dogs also wag their tails in response to non-social stimuli, such as food, fans and plastic bags, with tail wagging in these situations thought to indicate positive emotions and/or high arousal but not fear or stress.

The desirable features of our pets are primarily the result of genetic selection by humans together with adaption to a human-dominated environment.

Therefore over time any species that wanted to survive and be chosen as pets – with all the perks – had to find ways to get attention and appeal to their master’s selection criteria. Thus tameness and the ability to adapt to the human dominated environment developed.

In line with other domestication hypotheses, such as deferential behaviour and emotional reactivity, the altered tail-wagging behaviour seen in dogs could have arisen as a direct expression of docility or friendliness.

But still, human preferences would have likely played a role. A recent review of the science of tail-wagging led by biologist Silvia Leonetti of Italy’s University of Turin suggests that people may have selectively bred dogs to wag their tails because humans responded to the rhythmic nature of the tail wagging like they do to beats in music.

Cognitive neuroscience shows that human brains prefer rhythmic stimuli, which trigger pleasure responses and engage brain networks that are part of the reward system.

This propensity for regular rhythms could have driven human selection for the conspicuous rhythmic wagging of the tail in dogs and could explain why dogs exhibit it in human-dog interactions.

Next time you pick up that leash and your pooch starts thrumping the floor – that’s our Poppy’s word for rhythmic tail thumping on hardwood floors – consider that the domestication of your pet has evolved to such a sophisticated degree that your canine has learnt to manipulate and exploit the pleasure part of your brain.

Reference: Leonetti S, Cimarelli G, Hesh TA, Ravignani A. 2024 Why do dogs wag their tails?