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The dog evolved from the gray wolf into more than 400 distinct breeds. Human beings have played a major role in creating dogs that fulfill distinct societal needs. Through the most rudimentary form of genetic engineering, dogs were bred to accentuate instincts that were evident from their earliest encounters with humans. Although details about the evolution of dogs are uncertain, the first dogs were hunters with keen senses of sight and smell. Humans developed these instincts and created new breeds as need or desire arose. Friedmann E, Thomas SA (1995). "Pet ownership, social support, and one-year survival after acute myocardial infarction in the Cardiac Arrhythmia Suppression Trial (CAST)". The American Journal of Cardiology. 76 (#17): 1213–1217. doi: 10.1016/S0002-9149(99)80343-9. PMID 7502998. Ahmed Zihni (2004). "Dog Meat Dilemma". Stony Brook University – The Program in Writing and Rhetoric. Archived from the original on 11 August 2007 . Retrieved 11 May 2008.Kim Kavin (3 May 2016). The Dog Merchants: Inside the Big Business of Breeders, Pet Stores, and Rescuers. Simon and Schuster. ISBN 978-1-68177-170-0. Gompper, Matthew E. (2013). Free-Ranging Dogs and Wildlife Conservation (1ed.). Oxford University Press. p.128. ISBN 978-0-19-164010-0.

Additionally, the book offers expert information on everything from exercising and feeding your dog to grooming and puppy training, along with a section on care to help you identify and deal with any canine health problems.

Wayne, R.; Ostrander, Elaine A. (1999). "Origin, genetic diversity, and genome structure of the domestic dog". BioEssays. 21 (#3): 247–257. doi: 10.1002/(SICI)1521-1878(199903)21:3<247::AID-BIES9>3.0.CO;2-Z. PMID 10333734. S2CID 5547543. For thousands of years, humans bred dogs toward the physical and mental traits best suited for the work expected of them. The sleek Greyhound types bred to chase fleet-footed prey, and the huge mastiff types used as guard dogs and warriors, are two ancient examples of dogs bred for specific jobs. Scott, Jonathan; Scott, Angela (2006). Big Cat Diary: Leopard. London: Collins. p.108. ISBN 978-0-00-721181-4.

a b c Nast, Heidi J. (2006). "Loving... Whatever: Alienation, Neoliberalism and Pet-Love in the Twenty-First Century". ACME: An International e-Journal for Critical Geographies. 5 (#2): 300–327. ISSN 1492-9732. Further information: Canis lupus dingo §Taxonomic debate – the domestic dog, dingo, and New Guinea singing dogMorrison, Wallace B. (1998). Cancer in Dogs and Cats (1st ed.). Williams and Wilkins. ISBN 978-0-683-06105-5. Concannon, P; Tsutsui, T; Shille, V (2001). "Embryo development, hormonal requirements and maternal responses during canine pregnancy". Journal of Reproduction and Fertility. Supplement. 57: 169–179. PMID 11787146. In Korea, the primary dog breed raised for meat, the Nureongi, differs from those breeds raised for pets that Koreans may keep in their homes. [148] Gresky C, Hamann H, Distl O (2005). "[Influence of inbreeding on litter size and the proportion of stillborn puppies in dachshunds]". Berl. Munch. Tierarztl. Wochenschr. (in German). 118 (#3–4): 134–139. PMID 15803761.