The dog is part of a family of similar animals that include wolves, coyotes, foxes, jackals and wild hunting dogs such as the Dingo and African Wild Hunting Dog, who all share common characteristics. Many of these wild dogs have been claimed to be the domestic dog's wild ancestor but the exact origins of the dog and domestication history of the dog are uncertain.
Paleontologists and archaeologists have determined that Miacis, a weasel-like animal, is the ancestor of the canids as well as other families such as bears, raccoons, civets, hyenas and cats. From Miacis evolved Cynodictis, a dog-like animal from which later evolved the dog family.
All canids share common characteristics - they bear live young, have similar dental structures, walk on their toes rather than the soles of their feet, and are homeothermic (able to maintain their body temperature at a constant level).
Although hunting has been responsible for the development of many dog breeds, dogs were also used to aid humans in protecting and working with other domesticated animals kept by man and so guard dogs and herding dogs were developed. In addition breeds were also developed to aid humans in other activities such as sled dogs, war dogs, dogs of burden, guide and rescue dogs and toy dogs developed as small companion dogs.
As a result of the wide diversity of roles in which the dog has been selectively bred to perform over the years many different breeds of dog emerged throughout the world and exist today.
The domestic dog has been represented in art for many years with the earliest being sculptures of dogs found in Iraq and dating back to 6500 BC. Dog bones have been discovered dated at around 8300 BC in the USA, 7500 BC in the UK with similar finds in Czechoslovakia. One thing is certain, the domestic dog spread rapidly all over the world.
The dog's natural hunting instincts have been used by humans over the years to hunt a variety of prey in different environments and this led to the development of different groups of dogs, and ultimately to different dog breeds.
"Sight Hounds" or "Gaze Hounds" were an early group of dogs developed whose characteristics included a deep chest, long legs and a keen sense of sight. These dogs were used to spot prey from a distance and then to sprint swiftly and silently to run down prey in open, treeless countries. From this group dog breeds such as the Afghan, Saluki and Greyhound emerged.
"Scent Hounds" with an exceptional sense of smell provided by large noses with well opened nostrils were later developed in Europe. These dogs were not bred for speed but stamina, and were used to track and hunt prey over long periods of time. From this group of hounds dog breeds such as the Otter hound, Elkhound, Basset Hound and Dachshund emerged.
Hunting dogs were also developed, mostly in Britain, to hunt burrowing prey such as badgers, foxes and rabbits, and to control many types of vermin. These dogs needed to be feisty and energetic and so the group of dogs known as Terriers were developed. Most breeds of Terrier are descended from the Old English Black and Tan Terrier and the White English Terrier, both now extinct. Over the years two distinct types of terrier developed: smaller earth terriers with short legs who would go to ground after badgers, foxes and rabbits and larger terriers for hunting otters, water rats and wildlife that lived near rivers and around farms. Today many breeds of Terrier exist and these include the Fox Terrier, Welsh Terrier, Airedale Terrier and West Highland White Terrier.
Following the invention of the gun, dogs with sensitive noses were developed to locate and indicate the location of prey, to flush out prey or retrieve the prey once shot which required a soft mouth. For this purpose Pointers and Retrievers were developed.