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! 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. 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.