Most of the breeds of dogs, especially those of modern creation, are the work of man, and have been obtained by intercrossing older breeds and discarding all the animals that departed from the type sought.  But many of these breeds are also the result of accident, or rather of modifications of certain parts of the organism—­of a sort of rachitic or teratological degeneration which has become hereditary and has been due to domestication; for it is proved that the dog is the most anciently domesticated animal, and that its submission to man dates back to more than five thousand years.  Such is the origin of the breeds of terriers, bulldogs, and all of the small house dogs.

Man has often, designedly or undesignedly, aided in the production of breeds of this last category by submitting the dog to a regimen contrary to nature, or setting to work to reproduce an animal born monstrous, either for curiosity or for interest.  As well known, the accidental characters and the spontaneous modifications which work no injury to the essential functions of life became easily hereditary, and the same is the case with certain artificial modifications pursued for a long series of generations.

It was the opinion of Buffon that the breeds of dogs, which were already numerous in his time, were all derived from a single type, which, according to him, was the shepherd’s dog.  Other scientists have insisted that the dog descended from the wolf, and others from the jackal.  At the present time, it is rightly admitted that several species of wild dogs have concurred in the formation of the different breeds of dogs as we now have them.

In the lacustrine habitations of the stone age in Sweden, and in the kjoekkenmoedding (kitchen remains) of Denmark, of the same epoch, we find the remains of a dog, which, according to Rutymeyer, belongs to a breed which is constant up to its least details, and which is of a light and elegant conformation, of medium size, with a spacious and rounded cranium and a short, blunt muzzle, and a medium sized jaw, the teeth of which form a regular series.

This dog, which has been named by geologists Canis palustris, fully resembles in size, slenderness of the limbs, and weakness of the muscular insertions, the spaniel, the brach hound, or the griffon.

This dog of the stone age is entirely distinct from the wolf and jackal, of which some regard the domestic dog as a descendant, and as it has appeared in Denmark as well as in Sweden, there is no doubt that this species, peculiar to Europe, was subjugated by man and used by him, in the first place, for hunting, and later on for guarding houses and cattle.  Later still, in the age of metals, we observe the appearance, both in Denmark and Sweden, of larger and stronger breeds of dogs, having in their jaws the character of mastiffs, and probably introduced by the first emigrants from Asia.