^ Jump up to: a b Axelsson, E.; Ratnakumar, A.; Arendt, M.L.; Maqbool, K.; Webster, M.T.; Perloski, M.; Liberg, O.; Arnemo, J.M.; Hedhammar, Å.; Lindblad-Toh, K. (2013). "The genomic signature of dog domestication reveals adaptation to a starch-rich diet". Nature. 495 (7441): 360–364. Bibcode:2013Natur.495..360A. doi:10.1038/nature11837. PMID 23354050.

Every year, between 6 and 8 million dogs and cats enter US animal shelters.[204] The Humane Society of the United States (HSUS) estimates that approximately 3 to 4 million of those dogs and cats are euthanized yearly in the United States.[205] However, the percentage of dogs in US animal shelters that are eventually adopted and removed from the shelters by their new legal owners has increased since the mid-1990s from around 25% to a 2012 average of 40% among reporting shelters[206] (with many shelters reporting 60–75%).[207]
Humans would also have derived enormous benefit from the dogs associated with their camps.[136] For instance, dogs would have improved sanitation by cleaning up food scraps.[136] Dogs may have provided warmth, as referred to in the Australian Aboriginal expression "three dog night" (an exceptionally cold night), and they would have alerted the camp to the presence of predators or strangers, using their acute hearing to provide an early warning.[136]

The genetic divergence between dogs and wolves occurred between 40,000–20,000 years ago, just before or during the Last Glacial Maximum.[27][2] This timespan represents the upper time-limit for the commencement of domestication because it is the time of divergence and not the time of domestication, which occurred later.[27][28] The domestication of animals commenced over 15,000 years ago, beginning with the grey wolf (Canis lupus) by nomadic hunter-gatherers.[27] The archaeological record and genetic analysis show the remains of the Bonn–Oberkassel dog buried beside humans 14,200 years ago to be the first undisputed dog, with disputed remains occurring 36,000 years ago.[2] It was not until 11,000 years ago that people living in the Near East entered into relationships with wild populations of aurochs, boar, sheep, and goats.[27]
Neutering refers to the sterilization of animals, usually by removal of the male's testicles or the female's ovaries and uterus, in order to eliminate the ability to procreate and reduce sex drive. Because of the overpopulation of dogs in some countries, many animal control agencies, such as the American Society for the Prevention of Cruelty to Animals (ASPCA), advise that dogs not intended for further breeding should be neutered, so that they do not have undesired puppies that may later be euthanized.[74]
Dogs demonstrate a theory of mind by engaging in deception[89]. An experimental study showed compelling evidence that Australian dingos can outperform domestic dogs in non-social problem-solving, indicating that domestic dogs may have lost much of their original problem-solving abilities once they joined humans.[90] Another study indicated that after undergoing training to solve a simple manipulation task, dogs that are faced with an insoluble version of the same problem look at the human, while socialized wolves do not.[91] Modern domestic dogs use humans to solve their problems for them.[92][93]
Although dogs are the most abundant and widely distributed terrestrial carnivores, the potential of feral and free-ranging dogs to compete with other large carnivores is limited by their strong association with humans.[7] For example, a review of the studies in the competitive effects of dogs on sympatric carnivores did not mention any research on competition between dogs and wolves.[108][109] Although wolves are known to kill dogs, they tend to live in pairs or in small packs in areas where they are highly persecuted, giving them a disadvantage facing large dog groups.[108][110]
Coyotes and big cats have also been known to attack dogs. Leopards in particular are known to have a predilection for dogs, and have been recorded to kill and consume them regardless of their size.[114] Tigers in Manchuria, Indochina, Indonesia, and Malaysia are also reported to kill dogs.[115] Striped hyenas are known to kill dogs in Turkmenistan, India, and the Caucasus.[116]
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.[38] In some breeds, such as the Braque du Bourbonnais, puppies can be born with a short tail or no tail at all.[39]

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]
Wolves kill dogs wherever they are found together.[111] One study reported that in Wisconsin in 1999 more compensation had been paid for losses due to wolves taking dogs than for wolves taking livestock. In Wisconsin wolves will often kill hunting dogs, possibly because the dogs are in the wolf's territory.[111] A strategy has been reported in Russia where one wolf lures a dog into heavy brush where another wolf waits in ambush.[112] In some instances, wolves have displayed an uncharacteristic fearlessness of humans and buildings when attacking dogs, to the extent that they have to be beaten off or killed.[113] Although the numbers of dogs killed each year are relatively low, it induces a fear of wolves entering villages and farmyards to take dogs, and losses of dogs to wolves has led to demands for more liberal wolf hunting regulations.[108]

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