Scientists believe that dogs developed from a weasellike, meat-eating animal called Miacis, which lived about 50 million years ago. Miacis was the ancestor not only of dogs but also of cats, bears, raccoons, civets, weasels, and skunks. A descendant of Miacis called Tomarctus appeared about 15 million years ago. Tomarctus resembled a wolf and is the direct ancestor of all members of the dog family, including wolves, coyotes, jackals, foxes, and domestic dogs.

The oldest site where fossilized human and dog remains occur together dates from about 8000 B.C. This evidence indicates that people and dogs have lived with each other for at least 10,000 years, making the dog the oldest known domesticated animal. The saluki, which is probably the oldest of present-day breeds, may have originated in the Middle East as early as 7000 B.C. Paintings and sculpture from ancient Egypt indicate that the Egyptians had developed various dog breeds by about 1500 B.C. These artworks depict heavy dogs resembling mastiffs and hunting dogs with long legs and pointed noses.

The English physician John Caius, who also used the name Johannes Caius, wrote one of the first books about dogs in 1570. Caius describes 16 breeds, including terriers, spaniels, setters, bloodhounds, greyhounds, shepherds, and mastiffs. The first kennel clubs formed in Europe in the 1800's, and the first formal dog show took place in England in 1859 at Newcastle upon Tyne.

Scientific Classification. Dogs belong to the dog family, Canidae.

Terri McGinnis, "Dog," Discovery Channel School, original content provided by World Book Online, 6/18/2001.