Origin of Dogs:

Dogs are members of the order Carnivora, a group of mammals that originated about 55 million years ago. The current members of Carnivora include animals in the family Canidae. Wolves, jackals, and our dogs, among others animals, make up the family Canidae

The first of the Canidae, called Hesperocyon, lived about 25 to 30 million years ago in North America. Some Canidae migrated to South America where they evolved into foxes. Other Canidae gradually evolved into animals that began the genus Canis. These animals moved westward over the Bering Strait and continued into Eurasia.

The oldest representative of the Canis is Canis cipio; it was discovered in Concud, Spain. It lived about 6 million years ago. The genus continued evolving, producing Canis lupus, or wolf, about 300,000 years ago. The wolf is widely believed to be the forerunner of modern day dogs.

Because humans domesticated dogs about 20,000 years ago, we have no precise knowledge of how this was done. Presumably, young wolves were caught and raised in captivity. Then, humans would breed those animals that had the characteristics they wanted to keep. Over many generations, different types of dogs were developed -- those specialized for hunting, for guarding, and for sheep herding, among others.

Although most modern dog breeds were developed about 100 years ago and a few in the 1700s, these general dog classes -- hunters, guard dogs, and herders, have been known for thousands of years.