The dog is a type of canid, a mammal in the order Carnivora. The term includes both wild (feral) and domestic variants, but commonly excludes other canids such as wolves.
Over time, the dog has developed into hundreds of breeds with a great degree of variation.
Among dog lovers, dogs are generally valued for their intelligence. Both anecdotal evidence and scientific research suggest that dogs have a reasonably high intelligence. This intelligence is expressed differently with different breeds and individuals. Being highly adaptable animals themselves, dogs have learned to do a great number of very eclectic jobs, as man has required over the generations. Dogs are employed in various roles across the globe, proving invaluable assets in areas such as search-and-rescue. Other roles include law enforcement (including attack dogs, sniffer dogs and tracking dogs), guards for livestock, people or property, herding, Arctic exploration sled-pullers, guiding the blind and acting as a pair of ears for the deaf, assisting with hunting, and a great many other roles which they may be trained to assume. Dogs are descended from wolves, and are also pack animals. This makes them easier than other animals to train because dogs’ instincts are to obey. Most dogs rarely have to deal with complex tasks and are unlikely to learn relatively complicated activities (such as opening doors) unaided. Some dogs (such as guide dogs for the visually impaired) are specially trained to recognize and avoid dangerous situations.
Modern dog breeds show more variation in size, appearance, and behavior than any other domestic animal. Within the range of extremes, dogs generally share attributes with their wild ancestors, the wolves. Dogs are predators and scavengers, possessing sharp teeth and strong jaws. They are used for attacking, holding, and tearing their food. Although selective breeding has changed the appearance of many breeds, all dogs retain basic traits from their distant ancestors. Like many other predatory mammals, the dog has powerful muscles, fused wrist bones, a cardiovascular system that supports both sprinting and endurance, and teeth for catching and tearing. Compared to the bone structure of the human foot, dogs technically walk on their toes.
At present, there is some debate as to whether domestic dogs should be classified as omnivores or carnivores, by diet. The classification in the Order Carnivora does not necessarily mean that a dog’s diet must be restricted to meat. Unlike an obligate carnivore, a dog is dependent on neither meat-specific protein nor a very high level of protein in order to fulfill its basic dietary requirements. Dogs are able to healthily digest a variety of foods including vegetables and grains, and in fact can consume a large proportion of these in their diet. Wild canines not only eat available plants to obtain essential amino acids, but also obtain nutrients from vegetable matter from the stomach and intestinal contents of their herbivorous prey. Domestic dogs can survive healthily on a reasonable and carefully designed vegetarian diet, particularly if eggs and milk products are included. Dogs frequently avidly eat grass, which is a harmless activity
Common external parasites are various species of fleas, ticks, and mites. Internal parasites include hookworms, tapeworms, roundworms, and heartworms