Why does a dog wag its tail?
"Are you kidding?" you will say. "Why do you ask me such a simple question? Everyone knows the answer to that one! We find a dog wagging tail when it is happy."
And I would say that you are quite right; a dog does wag its tail because it is happy. But after all, that does not really answer the question. Suppose I ask it in a slightly different way: Why does a dog wag its tail when it is happy? Why doesn't it bob its head up and down? Why doesn't it scratch its ears? Why doesn't it stomp on its forelegs? Why doesn't it roll over on its back? Why doesn't it put a paw in its mouth, stick out its tongue, or wink an eye? Why, in particular, does it wag its tail when it is happy?
Now the question takes on more meaning. You see, it is a real, legitimate question—one that deserves a proper answer. When it was first asked of me, I was stumped cold. And I am a veterinarian. And I am supposed to know these things. . . .
The asking of the question of why a dog wags its tail immediately implies a second question. What we really want to know is how the whole business of tail-wagging in dogs started anyway. We want to know how tail-wagging originated and how it developed into the dog's way of expressing the emotion of happiness.
In order to answer this question adequately, we have to go back hundreds of thousands of years to those very early times in the history of living things, even before man inhabited the earth. We have learned from Charles Darwin and his concept of evolution that life in those days was pretty tough. It was a continuous struggle for existence and the quest for food was the paramount issue of the day. Most people have the wrong idea of what Darwin meant by this struggle for existence. They seem to think that it was just one long terrifying nightmare of repeated incidents of brutal bloodshed. If one animal met another, it was simply a fight to the finish. The strong would live and the weak would die and that was that. Well, nothing could be further from the truth. It was a struggle for existence between different species of animals rather than merely between individual animals. The members of the same species could not afford to fight each other. If they did, the species would soon die out. They had to raise families and provide food and shelter for them so that they could propagate the race. The animals of the same species cooperated with each other, hunted together, ate together, and protected each other from the attacks of other animals. It was easier to survive in this way, easier to hunt for food in a group than individually, easier to fight together than alone. So at best the struggle for existence was a part-time process. To be sure, there were plenty of fights within the species: fights for sexual conquest, for pack leadership, and for many other reasons. But, for the most part, the struggle for existence was reserved mainly for other kinds of animals. With one's own kind it was most often a matter of cooperation and the benefit of the group. True, there were certain species of animals that remained more or less solitary and never developed any cooperative activities with their own species to any appreciable degree. Most of these animals quickly became extinct, and they are the ones that are most often displayed in our larger museums. Some very remarkable few of these animals— like the cat—did actually come through somehow, and they are still with us. But, for the most part, those animals that secured for their species the best conditions of life were those in which the attribute of cooperation was most highly developed.
The ancestral dog cooperated with other dogs in the struggle for life by hunting in packs. If this cooperation was to be effective, these animals had to have some way of signaling each other. An obvious and common way of signaling was by means of the bark. We all know that the bark of the dog can mean many things. There is the bark of pleasure, the bark of pain, the bark of anger, the bark of expectancy, the bark of defiance, and the like. If we as human beings can understand the meaning of much of the barking of the dog, imagine how much more it means to a dog! Thus barking served as a very effective signal to other dogs that food was close at hand. On hearing the signal from one dog, the other members of the pack would rush to assist in tracking down the game.
Now what has all this to do with tail-wagging? While there is no doubt that the barking signal was very adequate in hunting certain types of game, it also had a limited effectiveness. Suppose the prospective game could fly, or climb a tree, or burrow its way into the ground? If such game were to hear the barking signal, it would simply disappear from the scene. Therefore a form of silent signal was also necessary. The tail of the dog served this function admirably. If the game was of the type that required silent pursuit, the dog that spotted the game would wag its tail violently as a signal to its fellows that a dainty morsel was close by. Now it is very unlikely that the dog figured this whole thing out logically. What is more probable is that it was a matter of instinct.
It is only a short jump from here to associate this dog wagging tail
activity with the feeling of happiness and well-being. Since the quest for food was uppermost in the life of the ancestral dog, the tracking down and acquisition of that food was one of the most exhilarating experiences the animal enjoyed. In time, the feeling of happiness and the wagging of the tail became intimately intertwined. As generations passed and instinctive behavior became more fully developed, the dog, while hunting, would wag its tail just for the pure joy of living, and even when the silent signal was not required. Of course, if the silent signal actually was required for particular game, the dog would make the proper use of it. Thousands of years later, long after the dog had become the companion of man and the silent signal no longer was essential to its existence, the dog still wagged its tail as a sign of pleasure.
The theory just presented has not been positively proven. But though it is merely a theory, the weight of the evidence is overwhelmingly in its favor. So when you see your dog wagging tail, you can be quite sure that it is not merely expressing enjoyment at the sight of its master, it is also unconsciously signaling its ancestral pack to assist in tracking down a delicious dinner, the devouring of which would be a festive occasion.
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