Domestic dog in the context of "Dog sense of smell"

Purported remains of Paleolithic dogs have been reported from several European archaeological sites dating to over 30,000 years ago. Their status as domesticated is highly controversial, with some authors suggesting them to be the ancestors of the domestic dog or an extinct, morphologically and genetically divergent wolf population.

The domestication of the dog was the process which led to the domestic dog. This included the dog's genetic divergence from the wolf, its domestication, and the emergence of the first dogs. Genetic studies suggest that all ancient and modern dogs share a common ancestry, descending from an ancient, now-extinct wolf population – or closely related wolf populations – which was distinct from the modern wolf lineage. The dog's similarity to the grey wolf is the result of substantial dog-into-wolf gene flow, with the modern grey wolf being the dog's nearest living relative. An extinct Late Pleistocene wolf may have been the ancestor of the dog.

The dog is a wolf-like canid. The genetic divergence between the dog's ancestor and modern wolves occurred between 20,000 and 40,000 years ago, just before or during the Last Glacial Maximum (20,000–27,000 years ago). This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence but not the time of domestication, which occurred later.

The dingo (either included in the species Canis familiaris, or considered one of the following independent taxa: Canis familiaris dingo, Canis dingo, or Canis lupus dingo) is an ancient (basal) lineage of dog found in Australia. Its taxonomic classification is debated as indicated by the variety of scientific names presently applied in different publications. It is variously considered a form of domestic dog not warranting recognition as a subspecies, a subspecies of dog or wolf, or a full species in its own right.

The dingo is a medium-sized canine that possesses a lean, hardy body adapted for speed, agility, and stamina. The dingo's three main coat colourations are light ginger or tan, black and tan, or creamy white. The skull is wedge-shaped and appears large in proportion to the body. The dingo is closely related to the New Guinea singing dog: their lineage split early from the lineage that led to today's domestic dogs, and can be traced back through Maritime Southeast Asia to Asia. The oldest remains of dingoes discovered in Australia are around 3,500 years old.

In the taxonomic treatment presented in the third (2005) edition of Mammal Species of the World, Canis lupus dingo is a taxonomic rank that includes both the dingo that is native to Australia and the New Guinea singing dog that is native to the New Guinea Highlands. It also includes some extinct dogs that were once found in coastal Papua New Guinea and the island of Java in the Indonesian Archipelago. In this treatment it is a subspecies of Canis lupus, the wolf (the domestic dog is treated as a different wolf subspecies), although other treatments consider the dog as a full species, with the dingo and its relatives either as a subspecies of the dog (as Canis familiaris dingo), a species in its own right (Canis dingo), or simply as an unnamed variant or genetic clade within the larger population of dogs (thus, Canis familiaris, not further differentiated). The genetic evidence indicates that the dingo clade originated from East Asian domestic dogs and was introduced through the Malay Archipelago into Australia, with a common ancestry between the Australian dingo and the New Guinea singing dog. The New Guinea singing dog is genetically closer to those dingoes that live in southeastern Australia than to those that live in the northwest.

In some countries, there is an overpopulation of pets such as cats, dogs, and exotic animals. In the United States, six to eight million animals are brought to shelters each year, of which an estimated three to four million are subsequently euthanized, including 2.7 million considered healthy and adoptable. Euthanasia numbers have declined since the 1970s, when U.S. shelters euthanized an estimated 12 to 20 million animals. Most humane societies, animal shelters, and rescue groups urge animal caregivers to have their animals spayed or neutered to prevent the births of unwanted and accidental litters that could contribute to this dynamic.

Dog crossbreeds (sometimes called designer dogs) are dogs which have been crossbred or selectively bred from two or more recognized dog breeds. Generally considered a specific type of mixed-breed dog, dog crossbreeds are not recognised as breeds in their own right, and do not necessarily breed true. However, historic crossbreeding has led to established breeds, such as the Cesky Terrier.

Dog crossbreeds are combinations of lineages of the domestic dog; they are distinguished from canid hybrids, which are interspecific crosses between Canis species (wolves, coyotes, jackals, etc.).