Researchers have put forward two possible reasons why dogs wag their tails.

Four experts came together to write a paper in Biology Letters on the enigma that is tail wagging, because while owners often gauge their pet’s mood by how fast a tail’s going, very little is known about why it happens.

Dr Taylor Hersh, from the Max Planck Institute for Psycholinguistics in the Netherlands, and her co-authors looked at more than 100 studies on why dogs wag their tails to come up with two hypotheses.

Both suggestions relate to how dogs have been domesticated and bred by humans for tens of thousands of years, slowly developing more tail-wagging tendencies than other types of canines.

‘Humans appreciate rhythms’

One of the theories, which they call “domesticated rhythmic wagging”, details how humans intentionally selected dogs for breeding who wagged their tails more frequently than others, simply because we like rhythmic sequences.

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

Humans either consciously or unconsciously made dogs this way because of how our brains are wired when it comes to appreciating rhythms, the experts suggest.

The paper states that this might explain why dogs wag their tails so often when interacting with humans.

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Effects of domestication

Alternatively, the experts suggest tail wagging in dogs increased over the domestication process simply as a “by-product of selection for other traits, such as docility and tameness”.

In other words, when humans started domesticating canines and breeding them to keep as pets, tail wagging essentially occurred as a side-effect (an adorable side-effect, but a side-effect nonetheless).

There would have been many changes to come from the domestication process, the experts say, which include fur depigmentation, reduced facial skeleton and teeth size, changes in overall body size, the emergence of physical attributes like floppy ears and curled tails and reduced brain size.

The paper concludes that while dog tail wagging is a prominent occurrence with our pets, it is still poorly understood scientifically and a lot more research would have to go into the subject for any concrete answers.

Does tail wagging actually mean a dog is happy?

It can, the paper says, but not always.

The experts believe it can indicate positive emotions and high arousal, and never fear or stress.

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However, tail wagging can also be used to convey information from dog to dog or dog to human, the paper says, such as showing a dog’s appeasement, submission or non-aggressive intent.

One study the paper references found that dogs may use tail wagging as a requesting signal. For example, if they want you to give them food, they may wag their tail to get your attention.

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