Dog behavior is the internally coordinated responses (actions or inactions) of the domestic dog (individuals or groups) to internal and/or external stimuli.[94] 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.[18] 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.[95]
Where the domestication of the dog took place remains debated, with the most plausible proposals spanning Western Europe,[9][28] Central Asia[28][29] and East Asia.[28][30] This has been made more complicated by the recent proposal that an initial wolf population split into East and West Eurasian groups. These two groups, before going extinct, were domesticated independently into two distinct dog populations between 14,000 and 6,400 years ago. The Western Eurasian dog population was gradually and partially replaced by East Asian dogs introduced by humans at least 6,400 years ago.[28][2] This proposal is also debated.[2]
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.[31] The tallest dog is a Great Dane that stands 106.7 cm (42.0 in) at the shoulder.[32]

Wolves, and their dog descendants, likely derived significant benefits from living in human camps – more safety, more reliable food, lesser caloric needs, and more chance to breed.[135] They would have benefited from humans' upright gait that gives them larger range over which to see potential predators and prey, as well as better color vision that, at least by day, gives humans better visual discrimination.[135] Camp dogs would also have benefited from human tool use, as in bringing down larger prey and controlling fire for a range of purposes.[135]

Dog communication is how dogs convey information to other dogs, how they understand messages from humans, and how humans translate the information that dogs are transmitting.[103]:xii Communication behaviors of dogs include eye gaze, facial expression, vocalization, body posture (including movements of bodies and limbs) and gustatory communication (scents, pheromones and taste). Humans communicate to dogs by using vocalization, hand signals and body posture.
The scientific evidence is mixed as to whether companionship of a dog can enhance human physical health and psychological wellbeing.[191] Studies suggesting that there are benefits to physical health and psychological wellbeing[192] have been criticised for being poorly controlled,[193] and finding that "the health of elderly people is related to their health habits and social supports but not to their ownership of, or attachment to, a companion animal." Earlier studies have shown that people who keep pet dogs or cats exhibit better mental and physical health than those who do not, making fewer visits to the doctor and being less likely to be on medication than non-guardians.[194]
Take extra care with dark-nailed dogs not to clip to the quick (blood vessel). Go slowly, and only take a little bit off at a time. Dremeling is much safer and easier to avoid hitting the quick, as it shaves only a little bit at a time. Use a cordless pet-safe Dremel tool, as the corded ones will not stop turning if they catch hair. Don't dremel for too long as it will burn the nail and prolong the trimming process for the dog which causes more stress. The best recommended process is trim first then dremel to shorten a little bit and round out the nail do it's not sharp.
A number of common human foods and household ingestibles are toxic to dogs, including chocolate solids (theobromine poisoning), onion and garlic (thiosulphate, sulfoxide or disulfide poisoning),[54] grapes and raisins, macadamia nuts, xylitol,[55] as well as various plants and other potentially ingested materials.[56][57] The nicotine in tobacco can also be dangerous. Dogs can be exposed to the substance by scavenging through garbage bins or ashtrays and eating cigars and cigarettes. Signs can be vomiting of large amounts (e.g., from eating cigar butts) or diarrhea. Some other signs are abdominal pain, loss of coordination, collapse, or death.[58] Dogs are susceptible to theobromine poisoning, typically from ingestion of chocolate. Theobromine is toxic to dogs because, although the dog's metabolism is capable of breaking down the chemical, the process is so slow that for some dogs even small amounts of chocolate can be fatal, especially dark chocolate.
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