Scientifically speaking, dogs evolved tails so they had a way to knock things off coffee tables – lacking proper hands, they really didn’t have any other way to do so!
I kid, I kid. The table-clearing function of a dog’s tail is a fringe benefit; the real reasons dogs have tails relate to their evolutionary history and ability to communicate. We’ll dive into the issue and explore the world of dog tails below, so keep reading.
The vast majority of vertebrates have tails. Humans are somewhat unique in that we lack tails as adults. We actually do have tails during the early stages of our development; but we usually absorb them before we’re born (occasionally babies are born with very small vestigial tails).
Several other primates also lack tails, as do most (but not all) frogs. But just about every other vertebrate bares a tail of one form or another. They may be short or long, prehensile or floppy, furry or naked; some even have really unusual tails, adapted for specific purposes.
Animals use their tails for a wide variety of purposes. Some use them for balance, while others as a form of defense. Still others use their tails to communicate with other animals, or to propel themselves through the water or across the ground.
Canids – the family that includes dogs, wolves, coyotes, foxes and other dog-like animals – primarily use their tails to communicate with others in their species (and humans, in the case of dogs).
This is not surprising, given the social nature of most canids, but dogs also use their tails to help maintain their balance while running and as rudders when swimming.
So, when you see your dog wagging, tucking or raising his tail, pay attention: He’s trying to tell you something!
Like cows, goats and other domestic animals, dogs been honed by tens of thousands of years of artificial, rather than natural, selection. If you’ll forgive the anthropomorphism: Natural selection occurs when Mother Nature decides which individuals live, breed, and die, while artificial selection occurs when humans make these decisions.
Because humans had very different goals than Mother Nature, the tails (and many other traits) of dogs began to change. As different breeds were created, their tails began to reflect the demands of the jobs the individual breeds were expected to perform. Accordingly, modern dogs exhibit remarkable diversity among their tails, and they vary in terms of length, shape, fur and the way in which it is carried.
The tails of whippets and greyhounds, for example, are long, taper strongly and often curl under the dogs’ bodies when they’re relaxed. Pugs, basenjis and a few others, by contrast, have tails that naturally curl over their backs. Some breeds have tails that even have flamboyantly furred tail, while others are largely devoid of hair.
Individuals of some breeds are occasionally born with naturally bobbed tails. This occurs due to natural genetic mutations. One of the most widespread mutations – the C189G mutation – causes naturally bobbed tails in at least 17 different breeds, including Australian shepherds and Pembroke Welsh corgis.
Dogs hold their tails differently depending on their mood, and this communicates their emotional state to other dogs and humans.
Some of the most common emotional states dogs relay with their tails are detailed below. Understand that dogs do not use their tails in a vacuum; they use them in conjunction with their eyes, ears, mouths and postures to communicate messages to others.
It’s pretty easy to interpret the broad message your dog is trying to convey by wagging his tail, but there are a number of subtle variations dogs display that, if correctly analyzed, can help provide additional detail to their message.
Consider the following subtleties alongside the tail posture and motion:
Height – Generally speaking, the height of the tail relates to the degree of enthusiasm or timidity. For example, a dog that is confident and secure will generally hold his tail high over his back, while a nervous dog will generally hold the tail lower.
Speed – Dogs that are excited wag their tails more rapidly than those who are not. This is easy to see with your own dog: When you prepare dinner, his tail will probably wag at a moderate speed; however, when you return home from work or grab his leash from the table, his tail will fly back and forth rapidly, in response to his excitement.
Stiffness – Dogs tend to exhibit more flexibility and less rigidity the more confident they feel. A dog whose body remains tense and tail completely straight is rarely feeling comfortable. On the flip side, thoroughly happy and comfortable dogs often wag their tail along its entire length. Sometimes, the wagging even encompasses the rear portion of their body (the “wiggle-but” phenomenon).
While a dog’s wagging tail may look like a chaotic mess of motion, there’s actually a bit of method interwoven with the madness.
A few years ago, scientists with the University of Trento in Italy started looking for patterns in the ways that dogs wagged their tails. And believe it or not, they found a pretty interesting pattern, hiding amidst the noise.
It turns out that dogs tend to wag their tails to the right when they are feeling positive and relaxed, while dogs tend to wave their tails to the left when they are nervous or anxious. What’s even more interesting is that dogs recognize these differences in other dogs.
This is not to suggest that dogs consciously wag their tails in either direction to purposely communicate their mood. Instead, it is likely an artifact of their dual-sided brains. Just like humans, dogs process different types of information in different halves of their brains.
When they are nervous, the right side of their brain is highly active; when relaxed, the left side of their brain is more active. And, like a lot of other bodily functions, these tendencies often manifest in the opposite half of the body. Meaning that when the right side of their brain is active, it causes their tail to move to the left, and vice versa.
Your dog’s tail provides a great window into his inner world, so be sure to note his tail while you are spending time together. With practice, you’ll be able to read your dog like a champ, and better tend to his needs.
Let us know how you interpret your dog’s tail wagging in the comments below!
Ben is a proud dog owner and lifelong environmental educator who writes about animals, outdoor recreation, science, and environmental issues. He lives with his beautiful wife and spoiled-rotten Rottweiler JB in Atlanta, Georgia. Read more by Ben at FootstepsInTheForest.com.