DOG

The domestic dog (Canis lupus familiaris when considered a subspecies of the wolf or Canis familiaris when considered a distinct species)is a member of the genus Canis (canines), which forms part of the wolf-like canids, and is the most widely abundant terrestrial carnivore. mThe dog and the extant gray wolf are sister taxa as modern wolves are not closely related to the wolves that were first domesticated, which implies that the direct ancestor of the dog is extinct. The dog was the first species to be domesticated and has been selectively bred over millennia for various behaviors, sensory capabilities, and physical attributes.

Their long association with humans has led dogs to be uniquely attuned to human behavior and they are able to thrive on a starch-rich diet that would be inadequate for other canid species. New research seems to show that dogs have mutations to equivalent genetic regions in humans where changes are known to trigger high sociability and somewhat reduced intelligence. Dogs vary widely in shape, size and colors. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship and, more recently, aiding handicapped individuals and therapeutic roles. This influence on human society has given them the sobriquet “man’s best friend”

In 1999, a study of mitochondrial DNA indicated that the domestic dog may have originated from multiple grey wolf populations, with the dingo and New Guinea singing dog “breeds” having developed at a time when human populations were more isolated from each other. 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: “familiaris Linneaus, 1758 [domestic dog]” and “dingoMeyer, 1793 [domestic dog]”. Wozencraft included hallstromi – the New Guinea singing dog – as a taxonomic synonym for the dingo. Wozencraft referred to the mDNA study as one of the guides in forming his decision. The inclusion of familiaris and dingo under a “domestic dog” clade has been noted by other mammalogists. This classification by Wozencraft is debated among zoologists.

Dogs are highly variable in height and weight. The smallest known adult dog was a Yorkshire Terrier, that stood only 6.3 cm (2.5 in) at the shoulder, 9.5 cm (3.7 in) in length along the head-and-body, and weighed only 113 grams (4.0 oz). The largest known dog was an English Mastiff which weighed 155.6 kg (343 lb) and was 250 cm (98 in) from the snout to the tail. The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder.

Despite their close genetic relationship and the ability to inter-breed, there are a number of diagnostic features to distinguish the gray wolves from domestic dogs. Domesticated dogs are clearly distinguishable from wolves by starch gel electrophoresis of red blood cell acid phosphatase. The tympanic bullae are large, convex and almost spherical in gray wolves, while the bullae of dogs are smaller, compressed and slightly crumpled. Compared with equally sized wolves, dogs tend to have 20% smaller skulls and 30% smaller brains.:35 The teeth of gray wolves are also proportionately larger than those of dogs. Dogs have a more domed forehead and a distinctive “stop” between forehead and nose. The temporalis muscle that closes the jaws is more robust in wolves.:p158 Wolves do not have dewclaws on their back legs, unless there has been admixture with dogs that had them. Most dogs lack a functioning pre-caudal gland and enter estrus twice yearly, unlike gray wolves which only do so once a year. So-called primitive dogs such as Dingoes and Basenjis retain the yearly estrus cycle.

Dogs generally have brown eyes and wolves almost always have amber or light colored eyes. The skin of domestic dogs tends to be thicker than that of wolves, with some Inuit tribes favoring the former for use as clothing due to its greater resistance to wear and tear in harsh weather. The paws of a dog are half the size of those of a wolf, and their tails tend to curl upwards, another trait not found in wolves. The dog has developed into hundreds of varied breeds, and shows more behavioral and morphological variation than any other land mammal. For example, height measured to the withers ranges from a 6 inches (150 mm) in the Chihuahua to 3.3 feet (1.0 m) in the Irish Wolfhound; color varies from white through grays (usually called “blue”) to black, and browns from light (tan) to dark (“red” or “chocolate”) in a wide variation of patterns; coats can be short or long, coarse-haired to wool-like, straight, curly, or smooth. It is common for most breeds to shed their coat.

Golden Retriever gnawing a pig’s foot

Dogs have been described as carnivores or omnivores. Unlike obligate carnivores, domestic dogs (and wild canids) can adapt to a wide-ranging diet, and are not dependent on meat-specific protein nor a very high level of protein in order to fulfill their basic dietary requirements. Dogs can healthily digest a variety of foods, including vegetables, fruits and grains, and can consume a large proportion of these in their diet, and some sources do not recommend all-meat diets for dogs, due to their lack of calcium and iron. Compared to wolves, dogs have genes involved in starch digestion that contribute to an increased ability to thrive on a starch-rich diet.