Today, the dog is a house pet in most places and food in others. Where dogs came from (and how they became ubiquitous) is really the story of man himself.

At the dawn of man, there were no dogs; only wolves. DNA research, notably by Dr. Robert K. Wayne at UCLA, established that the ancestor of today's dogs is the Grey Wolf (Canis Lupus). Archaeological evidence of dogs in human settlements go back more than ten thousand years, proof we have a longer relationship with the dog than with any other animal.

Imagine our ancestors after a successful hunt, gathered around a large fire, roasting the beast they've slain, tearing off pieces to eat. The smell of that barbecue drew other predators from miles around, salivating and hoping for the remains once the humans were finished. A pack of Grey wolves hovers just out of range of the fire's light, seeking a way to be the first at the carcass. One wolf — perhaps the hungriest, maybe just the smartest — begins to creep submissively towards the fire and the people. When yelled at to go away, instead of running back to the pack, this wolf rolls over and smiles, eliciting giggles from the humans. A few more steps forward and the humans again yell at the wolf, tossing a stone or two to scare it off. Again, this wolf doesn't run; this time it sits up on its hind legs and claps its paws; now the humans are delighted. One of those laughing humans throws the goofy wolf a tidbit of meat. Thus begins our relationship with what will evolve to be today's dog.

The goofy wolf overcame our initial reservation by making us laugh; it earned our appreciation by helping us hunt, and it secured its place at our hearth and in our home when it protected us from attackers, both human and animal.

Breeding over time would have been somewhat simplistic: the humans would have kept descendants of the first wolf that had the same traits and would have likely killed and eaten any offspring that were too 'wild'. In a very short time, the kept wolves would evolve in dozens of ways, large and small. They'd get dense coats in some places, keen eyesight in others. Now imagine this happening in different groups of people throughout man's early years. Tribes of humans living in frigid northern lands end up with thick-furred animals with poor eyesight while groups of humans living in equatorial zones have sleek, short haired dogs with excellent distance vision. Fast forward ten thousand years or so and those differences form the beginnings of today's diverse breeds.

Of course, that's just one hypothesis — feel free to imagine others. Maybe a group of humans came upon an orphaned litter of wolf puppies and brought them back to their encampment, raising them to be companions, hunting partners and protectors. What we know for certain is that dogs descended from the Grey Wolf and the two still share enough genetic commonality that they can interbreed today.

Canis lupus familiaris — the dog — is, therefore, a domesticated subspecies of the wolf; a mammal of the Canidae family (mammal meaning warm blooded and giving birth to live young) of the order Carnivora.

The word 'dog' is used for more than our companions. There are still wild breeds where we use the term despite them being members of other subspecies or species. For example, in the American West, Prairie Dogs dot the open range. They aren't dogs at all — they're rodents, members of the squirrel family.

The dog has developed into hundreds of breeds with a staggering variety and range. From the tiny Chihuahua to the giant Irish Wolfhound in terms of size, there is just as much difference in color — think of the snow white Samoyed compared to the gleaming black Doberman. Their coats can be almost non-existent (the Chinese Hairless) to completely encompassing (the Puli). The American Kennel Club (AKC) recognizes 157 breeds of dog today; some estimate that there may be another 300 breeds in addition to that number.

1. Etymology and related terminology
2. Taxonomy
3. Origin and evolution
• Origins
• Domestication: history and ancestry
• Breed development
• Breeds ranked by popularity
4. Physical characteristics
• Dogs are different
• Eyesight
• Hearing
• Smell
• Color
• Heads you lose, tails you win
• Sprint metabolism
5. Behavior and intelligence
• The scale of canid intelligence
• Evaluation of a dog's intelligence
• Human relationships
• Differences from other canids
• Life cycle
6. Reproduction
• Overpopulation
• United States
7. Working, utility and assistance dogs
8. Show and sport (competition) dogs
9. Dog health
• Morbidity
• Illness
• Diseases
• Parasites
• Chronic conditions
• Predation
• Diet: Nutrition
• Diet dangers
• Dog abuse
• Dogs as Livestock

Etymology and related terminology

It appears that initially, 'dog' was used to refer to particularly large canines, but even in that use, the origin of the word is obscure: there is no known root for the word 'dog' in any language. Several European languages have cognates of dog, but these are all descended from the English word and provide no clue as to the word's original provenance. In one document, dated from late in the Old English period (approximately 1050) the word dog appears, specifically written as "canum docgena."

Before that date, in Old English as well as in other European tongues, the most common word used to refer to this animal was hund, the word that evolved in English to hound. Hound is cognate to other Germanic terms, including the German Hund, the Dutch hond, the common Scandinavian hund and the Icelandic hundur which, though referring to a specific breed group in English, means a generic 'dog' in the other Germanic languages. Hund can be dated back to the year 857 and perhaps even earlier. At that point, it referred to any canine, but after a few centuries, hund evolved to mean only the dogs used in the hunt. By 1200, that meaning focused only on hunting dogs that followed prey via scent. As it became obvious that other hunting dogs followed the prey by sight, there was a brief period when hund referred to both. In the modern era, the terms scent hound and sight hound came into use to differentiate between the two types.

Today, dog is commonly used to refer to any dog, but in breeder and show circles, dog refers to males only; the female counterpart is bitch. The father of a litter is called the sire, the mother of a litter is called the dam. Offspring are generally called pups or puppies until one year of age; in larger breeds the term puppy may be idiomatically used to denote their slow maturation. The process of birth is whelping; the group of puppies resulting from the birth is called a litter. Many terms are used for dogs that are not purebred (mongrels, mutts and more). Dog is also the term used for the male of several other species, including foxes.

(Bitch, spelled bicce, is found in Old English circa 1000. It has one known cognate, the Old Norse bikkja, but the origin of the Norse word is unknown. There's conjecture as to whether one or the other may derive from the Lappish pittja, but the since reverse could also be true there's little sense in the debate right now. And in case you were wondering, bitch as a derogatory term for a woman dates to sometime before 1400.)

Going back to the word dog, the ongoing presence of these animals in our lives has given them a constant presence in our language. You can go to the dogs (1565) or lead a dog's life (1764). We are cautioned to let sleeping dogs lie (1562) and advised to take a hair of the dog that bit you (1546) after indulging in too much drink on the previous evening. Some usages have lost favor — for example, the phrase, 'like a dog in the manger' (1573) arose from a fable popular in the 16th century. In that story, a dog stopped the other animals from eating even though it had no interest in the fodder itself. Newly coined definitions include rap music's use of the word 'dog' to denote a man who deceptively uses multiple women for his own pleasure; the WWII phrase "my dogs are killing me" to indicate sore feet. A three-dog night is an evening so cold, humans want three dogs in their bed to help keep warm!

As a verb, 'to dog' means to follow closely and persistently (1519). It can also mean to close and secure a door or opening (1591), after the name of a type of clamp likened to a canine because of its jaws and teeth. In 20th century American slang, to dog it means perform lazily or shirk one's duties. Police officers must doggedly pursue criminals, meaning with ceaseless dedication.

Taxonomy

The English word dog, in common usage, refers to the domestic pet dog, Canis lupus familiaris. The species was originally classified as Canis familiaris and Canis familiarus domesticus by Linnaeus in 1758. In 1993, dogs were reclassified as a subspecies of the Grey Wolf, Canis lupus, by the Smithsonian Institution and the American Society of Mammalogists thanks to the work of UCLA's Dr. Robert K. Wayne. Dog is sometimes used to refer collectively to any mammal belonging to the family Canidae (as in "the dog family"), such as wolves, foxes, and coyotes. Some members of the family have "dog" in their common names, such as the Raccoon Dog and the African Wild Dog.