Dog

10-13 years

Dog is an omnivorous species primarily reliant on a meat-based diet. Notably, their preferred food includes chicken, beef, and fish alongside fruits, vegetables, and grains, contributing to a balanced dietary regime.

The smallest known adult dog was a Yorkshire Terrier, that stood only 6 cm at the shoulder, 9 cm in length along the head-and-body, and weighed only 113 grams. The largest known dog was an English Mastiff which weighed 155.6 kg and was 2.5 m from the snout to the tail. The tallest dog is a Great Dane that stands 1.07 m at the shoulder.

The coats of domestic dogs are of two varieties: "double" being common 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.

Premature graying can occur in dogs from as early as one year of age. This has been shown to be associated with impulsive behaviors, anxiety behaviors, fear of noise, and fear of unfamiliar people or animals.

There are many different shapes for dog tails: straight, straight up, sickle, curled, or cork-screw. As with many canids, one of the primary functions of a dog's tail is to communicate their emotional state, which can be important in getting along with others. In some hunting dogs, however, the tail is traditionally docked to avoid injuries. In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.

Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli. As the oldest domesticated species, with estimates ranging from 9,000–30,000 years BCE, the minds of dogs inevitably have been shaped by millennia of contact with humans. As a result of this physical and social evolution, dogs, more than any other species, have acquired the ability to understand and communicate with humans, and they are uniquely attuned to human behaviors. Behavioral scientists have uncovered a surprising set of social-cognitive abilities in the domestic dog. These abilities are not possessed by the dog's closest canine relatives nor by other highly intelligent mammals such as great apes but rather parallel some of the social-cognitive skills of human children.

Unlike other domestic species which were primarily selected for production-related traits, dogs were initially selected for their behaviors. In 2016, a study found that there were only 11 fixed genes that showed variation between wolves and dogs. These gene variations were unlikely to have been the result of natural evolution, and indicate selection on both morphology and behavior during dog domestication. These genes have been shown to affect the catecholamine synthesis pathway, with the majority of the genes affecting the fight-or-flight response (i.e. selection for tameness), and emotional processing. Dogs generally show reduced fear and aggression compared with wolves. Some of these genes have been associated with aggression in some dog breeds, indicating their importance in both the initial domestication and then later in breed formation. Traits of high sociability and lack of fear in dogs may include genetic modifications related to Williams-Beuren syndrome in humans, which cause hypersociability at the expense of problem solving ability.