Why Dogs Wag Their Tails

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It is not just about expressing their joy

Contrary to popular perception, dogs do not wag their tails just to express their joy at meeting their masters. A new study has found that dogs communicate a lot more information about their emotions through their tails. When dogs wag their tails to the right side, it is because they are experiencing a positive emotion, for instance that of meeting their masters. When they wag their tails towards the left, it is because they are undergoing a negative emotion, like the presence of an unfamiliar and hostile dog in its surroundings. The researchers also found that other canines can spot and respond to these subtle tail differences.

The study was conducted by neuroscientists at University of Trento in Italy and published in the journal Current Biology. They found that dogs have asymmetrically organised brains, just like humans, with the left and right sides playing different roles. For dogs the right side of the brain was responsible for left-handed movement and vice versa, and the two hemispheres played different roles in emotions.

To find out how dogs react to the manner in which other dogs wag their tails, the researchers measured the heart rates and analysed their behaviour as they watched videos of other dogs wagging their tails. The dogs being studied remained in a calm and relaxed position while watching videos where the dog on screen moved its tail to the right side. But when the dog on screen veered its tail to the left, the heart rate of the dogs being studied picked up and they appeared anxious, signifying that dogs can pick up differences in tail wags of dogs.

The researchers are not convinced that dogs intentionally communicate with each other through their tail movements, as, they say, these movements could be the result of the manner in which their brains are wired. Other canines in all likelihood simply learnt of these movements and what they signify through experience. The lead researcher, Professor Giorgio Vallortigara, told The Telegraph, “We know from neurological studies in humans that the left and right hemispheres in the brain produce different emotional responses... In dogs, single organs like the tongue or tail is controlled by both sides of the brain. There can be competition and dominance between these two sides. When they move their tail, it is more bias to the left or to the right depending on which side of the brain is more dominant at the time. It seems dogs pick up on this when they meet other dogs and it forms a type of communication between them.”