Why do pets have tails - and why don’t people?

Most animals, and certainly almost all mammals and fish, have a tail. This is something that we generally take for granted, and in animals such as cats and dogs, some of the reasons for why they have a tail as part of their anatomy is clear- signalling like and dislike, happiness, annoyance and many other feelings to both people and other pets. Aside from this, however, it is perhaps not always obvious what the function of the tails of some animals are, and why tails evolved at all. Evolutionary theory tells us that over the course of centuries and millennia, all living creatures adapt and develop in a way that suits their living environment and gives them the best chances of survival and healthy living. This is why some reptiles can change the colour of their skin to blend into the background; and why ducks and other waterfowl have webbed feet to help them swim.But what about the tail? What are some of the functions of the tail in different animals? Moreover, why don’t humans have, or need, a tail as well? Read on to find out more!

What exactly is a tail?

The question of ‘what exactly is a tail’ might seem to be rather obvious- it is the protrusion that hangs down at the back of the pet, right? This certainly is generally correct, but rather simplistic- there is more to the tail than meets the eye! Tails are flexible, and capable of independent movement (like the legs) and are comprised of bone along at least part of the structure (extending from the spine) as well as muscle tissue, ligament and fat. The area where the tail meets the body is known as the coccyx, often colloquially referred to as the tailbone. Animals with tails are referred to as ‘caudate,’ and the area around the tail is known as the caudal area.

What does a tail do?

The full range of functions of the tail varies from animal to animal. In many animals, the tail is a vital part of balance and movement, and many animals actively use their tail to keep themselves stable when walking along narrow surfaces or above the ground.

• In birds, the tail helps them to fly by providing steerage and balance, as well as contributing to the flat aerodynamic surface that helps to keep the bird in flight.
• In horses, the tail is invaluable to help swat at flies that land on the body, and to protect the back end.
• In cats, the tail is vital to assist with balance, as well as being an important communication tool. A swishing tail often denotes irritation, while the tail can bush up to three or more times its original size to make a defensive cat appear larger and more threatening to predators and other threats.
• Dogs speak a whole language with their tails, and you can often identify the mood of your dog at a glance simply by looking at what their tail is doing. Also, the tail protects the region of the anal glands, which give off your dog’s scent to other dogs. Clamping the tail down helps to reduce your dog’s signature scent and help to mask them from other animals.
• Fish use their tail like a rudder; or it would be more accurate to say that rudder development owes a lot to the observation of the tails of fish! Fishes’ tails help them to move through the water and provide direction.
• Many animals such as monkeys have a particularly impressive tail function- it can grasp and hold onto objects and perform almost like having an extra hand. A tail that can do this is called a prehensile tail, taken from the Latin phrase prehendere, meaning to grasp or hold on. This helps monkeys and other animals with prehensile tails such as snakes and rats to move through trees high above the ground, or hold objects.

Why don’t people have tails?

It may surprise you to learn that the early ancestors of the Homo sapiens that we are today, almost certainly had a tail of some sort. Over time as we evolved, the need for this tail structure disappeared, and so we slowly evolved away from having one! Humans still have a coccyx or tailbone, and in growing embryos in the womb, a tail structure develops during the first trimester. This is then re-absorbed into the body as the foetus develops before birth. The human tailbone, unlike that of animals that display an external tail, is contained within the spine as fused vertebrae, and does not hang down the back or have free movement like the tailbone area of animals.

What about animals that are docked or have lost their tails?

Tail docking, the process of physically cutting off or otherwise removing the tails of certain breeds and types of dogs, is now illegal within the UK, and so it is relatively uncommon to see a pet that does not have a tail. But various accidents, injuries or genetic abnormalities (such as the perceived desirable genetic abnormality that leads to the Manx breed of cat being born with mutated tails) means that they do occasionally appear. In domestic pets such as cats and dogs, learning to live without a tail is relatively straightforward, as domestic pets no longer have to rely on their tails for balance, to signal warnings and for many other functions. Domestic cats without tails may be very slightly less sure-footed than cats with tails, but this very rarely seems to stop them from getting into mischief!Reading the signs and communication cues from a dog with no tail can be a challenge, although in time you will easily be able to judge your dog’s moods and feelings by other means, and also, they will still be able to communicate as normal if a small part of the tail still remains.If your pet has a break or injury to their tail, it is important to take them to the vet as soon as possible. Remember that the tail is flexible and contains a range of bones, ligaments and muscles, and so should be treated with the same urgency as a broken or injured limb, and not just left in the hope that it will recover on its own.