Why does a dog wag
"Are you kidding?" you will say. "Why do you ask me such a simple
question? Everyone knows the answer to that one! A dog wags its tail
simply because 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.
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.
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
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
It is only a short jump from here to associate this tail-wagging
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
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 your pooch wags its 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