10 Hot Dogs

[Temika]

All dogs descend from a species of wolf, but not the gray wolf (Canis lupus), like many people assume. In fact, DNA evidence suggests that the now-extinct wolf ancestor to modern dogs was Eurasian. However, scientists are still working to understand exactly what species gave rise to dogs.

Similarly, humans bred German shepherds for their ability to herd livestock, Labrador retrievers to help collect ducks and other game felled by hunters, and sausage-shaped Dachshunds for their ability to rush down a burrow after a badger. Many more breeds were created to fill other human needs, such as home protection and vermin control.

Certain breeds have also been created to make dogs more desirable as companions. For instance, the labradoodle, which combines the traits of a Labrador retriever and a poodle, was invented as an attempt to create a hypoallergenic guide dog.

They assist search and rescue teams in the wake of natural disasters or reports of people lost in the outdoors. Dogs trained to warn of hidden explosives and enemies serve as allies in military operations. Other dogs assist police looking for jail escapees or the bodies of murder victims. Some partner instead with customs officials searching for contraband, from drugs to elephant ivory. Still others lead the way tracking down poachers, patrolling cargo ships for rats that might escape at distant harbors, or exposing forest insect pests in shipments of wood from abroad.

Editor's note: Bringing a dog into your household is a major responsibility. More than 1.6 million dogs ended up in shelters in 2020. Learn how to keep your dog happy and healthy with the National Geographic book Complete Guide To Pet Health, Behavior, and Happiness.

The dog (Canis familiaris or Canis lupus familiaris) is a domesticated descendant of the wolf. Also called the domestic dog, it was domesticated from an extinct population of Pleistocene wolves over 14,000 years ago. The dog was the first species to be domesticated by humans. Experts estimate that hunter-gatherers domesticated dogs more than 15,000 years ago, which was before the development of agriculture. Due to their long association with humans, dogs have expanded to a large number of domestic individuals and gained the ability to thrive on a starch-rich diet that would be inadequate for other canids.[4]

In 1758, the Swedish botanist and zoologist Carl Linnaeus published in his Systema Naturae, the two-word naming of species (binomial nomenclature). Canis is the Latin word meaning "dog",[7] and under this genus, he listed the domestic dog, the wolf, and the golden jackal. He classified the domestic dog as Canis familiaris and, on the next page, classified the grey wolf as Canis lupus.[2] Linnaeus considered the dog to be a separate species from the wolf because of its upturning tail (cauda recurvata in Latin term), which is not found in any other canid.[8]

In 1999, a study of mitochondrial DNA (mtDNA) indicated that the domestic dog may have originated from the grey wolf, with the dingo and New Guinea singing dog breeds having developed at a time when human communities were more isolated from each other.[9] In the third edition of Mammal Species of the World published in 2005, the mammalogist W. Christopher Wozencraft listed under the wolf Canis lupus its wild subspecies and proposed two additional subspecies, which formed the domestic dog clade: familiaris, as named by Linnaeus in 1758, and dingo, named by Meyer in 1793. Wozencraft included hallstromi (the New Guinea singing dog) as another name (junior synonym) for the dingo. Wozencraft referred to the mtDNA study as one of the guides informing his decision.[3] Mammalogists have noted the inclusion of familiaris and dingo together under the "domestic dog" clade[10] with some debating it.[11]

In 2019, a workshop hosted by the IUCN/Species Survival Commission's Canid Specialist Group considered the dingo and the New Guinea singing dog to be feral Canis familiaris and therefore did not assess them for the IUCN Red List of Threatened Species.[12]

The earliest remains generally accepted to be those of a domesticated dog were discovered in Bonn-Oberkassel, Germany. Contextual, isotopic, genetic, and morphological evidence shows that this dog was not a local wolf.[13] The dog was dated to 14,223 years ago and was found buried along with a man and a woman, all three having been sprayed with red hematite powder and buried under large, thick basalt blocks. The dog had died of canine distemper.[14] Earlier remains dating back to 30,000 years ago have been described as Paleolithic dogs, but their status as dogs or wolves remains debated[15] because considerable morphological diversity existed among wolves during the Late Pleistocene.[1]

This timing indicates that the dog was the first species to be domesticated[16][17] in the time of hunter-gatherers,[18] which predates agriculture.[1] DNA sequences show that all ancient and modern dogs share a common ancestry and descended from an ancient, extinct wolf population that was distinct from any modern wolf lineage. Some studies have posited that all living wolves are more closely related to each other than to dogs,[19][18] while others have suggested that dogs are more closely related to modern Eurasian wolves than to American wolves.[20]

The dog is a classic example of a domestic animal that likely travelled a commensal pathway into domestication.[15][21] The questions of when and where dogs were first domesticated have taxed geneticists and archaeologists for decades.[16] Genetic studies suggest a domestication process commencing over 25,000 years ago, in one or several wolf populations in either Europe, the high Arctic, or eastern Asia.[22] In 2021, a literature review of the current evidence infers that the dog was domesticated in Siberia 23,000 years ago by ancient North Siberians, then later dispersed eastward into the Americas and westward across Eurasia,[13] with dogs likely accompanying the first humans to inhabit the Americas.[13] Some studies have suggested that the extinct Japanese wolf is closely related to the ancestor of domestic dogs.[23]

Dogs are the most variable mammal on earth, with around 450 globally recognized dog breeds.[22][24] In the Victorian era, directed human selection developed the modern dog breeds, which resulted in a vast range of phenotypes.[17] Most breeds were derived from small numbers of founders within the last 200 years.[17][22] Since then, dogs have undergone rapid phenotypic change and have been subjected to artificial selection by humans. The skull, body, and limb proportions between breeds display more phenotypic diversity than can be found within the entire order of carnivores. These breeds possess distinct traits related to morphology, which include body size, skull shape, tail phenotype, fur type, and colour.[17] Their behavioural traits include guarding, herding, hunting,[17] retrieving, and scent detection. Their personality traits include hypersocial behavior, boldness, and aggression.[17] Present-day dogs are dispersed around the world.[22] An example of this dispersal is the numerous modern breeds of European lineage during the Victorian era.[18]

Dogs are extremely variable in size, ranging from one the largest breeds, the great dane, at 50 to 79 kg (110 to 174 lb) and 71 to 81 cm (28 to 32 in), to one of the smallest, the chihuahua, at 0.5 to 3 kg (1.1 to 6.6 lb) and 13 to 20 cm (5.1 to 7.9 in).[25][26] All healthy dogs, regardless of their size and type, have an identical skeletal structure with the exception of the number of bones in the tail, although there is significant skeletal variation between dogs of different types.[27][28] The dog's skeleton is well adapted for running; the vertebrae on the neck and back have extensions for back muscles, consisting of epaxial muscles and hypaxial muscles, to connect to; the long ribs provide room for the heart and lungs; and the shoulders are unattached to the skeleton, allowing for flexibility.[27][28][29]

Compared to the dog's wolf-like ancestors, selective breeding since domestication has seen the dog's skeleton larger in size for larger types such as mastiffs and miniaturised for smaller types such as terriers; dwarfism has been selectively used for some types where short legs are advantageous, such as dachshunds and corgis.[28] Most dogs naturally have 26 vertebrae in their tails, but some with naturally short tails have as few as three.[27]

The dog's skull has identical components regardless of breed type, but there is significant divergence in terms of skull shape between types.[28][30] The three basic skull shapes are the elongated dolichocephalic type as seen in sighthounds, the intermediate mesocephalic or mesaticephalic type, and the very short and broad brachycephalic type exemplified by mastiff type skulls.[28][30] The jaw contains around 42 teeth, and is designed for the consumption of flesh. Dogs use their carnassial teeth to cut food into bite-sized chunks, more especially meat.[31]

Dogs' senses include vision, hearing, smell, taste, touch, and magnetoreception. One study suggests that dogs can feel small variations in Earth's magnetic field.[32] Dogs prefer to defecate with their spines aligned in a north-south position in calm magnetic field conditions.[33]

The coats of domestic dogs are of two varieties: "double" being familiar with dogs (as well as wolves) originating from colder climates, made up of a coarse guard hair and a soft down hair, or "single", with the topcoat only. Breeds may have an occasional "blaze", stripe, or "star" of white fur on their chest or underside.[35] Premature graying can occur in dogs as early as one year of age; this is associated with impulsive behaviors, anxiety behaviors, and fear of unfamiliar noise, people, or animals.[36] Some dog breeds are hairless, while others have a very thick corded coat. The coats of certain breeds are often groomed to a characteristic style, for example, the Yorkshire terrier's "show cut".[31]

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