The origin of the domestic dog includes the dog's evolutionary divergence from the wolf, its domestication, and its development into dog types and dog breeds. The dog is a member of the genus Canis, which forms part of the wolf-like canids, and was the first species and the only large carnivore to have been domesticated. The dog and the extant gray wolf are sister taxa, as modern wolves are not closely related to the population of wolves that was first domesticated.
In Christianity, dogs represent faithfulness. Within the Roman Catholic denomination specifically, the iconography of Saint Dominic includes a dog, after the hallow's mother dreamt of a dog springing from her womb and becoming pregnant shortly thereafter. As such, the Dominican Order (Ecclesiastical Latin: Dominicanus) means "dogs of the Lord" or "hounds of the Lord" (Ecclesiastical Latin: domini canis). In Christian folklore, a church grim often takes the form of a black dog to guard Christian churches and their churchyards from sacrilege.
^ Bridgett M. von Holdt, Emily Shuldiner, Ilana Janowitz Koch, Rebecca Y. Kartzinel, Andrew Hogan, Lauren Brubaker, Shelby Wanser4, Daniel Stahler, Clive D.L. Wynne, Elaine A. Ostrander, Janet S. Sinsheimer and Monique A.R. Udell (19 July 2017). "Structural variants in genes associated with human Williams-Beuren syndrome underlie stereotypical hypersociability in domestic dogs". Science Advances. 3 (7): e1700398. Bibcode:2017SciA....3E0398V. doi:10.1126/sciadv.1700398. PMC 5517105. PMID 28776031.
In domestic dogs, sexual maturity happens around six to twelve months of age for both males and females, although this can be delayed until up to two years old for some large breeds. This is the time at which female dogs will have their first estrous cycle. They will experience subsequent estrous cycles semiannually, during which the body prepares for pregnancy. At the peak of the cycle, females will come into estrus, being mentally and physically receptive to copulation. Because the ova survive and are capable of being fertilized for a week after ovulation, it is possible for more than one male to sire the same litter.
^ vonHoldt, Bridgett M.; Shuldiner, Emily; Koch, Ilana Janowitz; Kartzinel, Rebecca Y.; Hogan, Andrew; Brubaker, Lauren; Wanser, Shelby; Stahler, Daniel; Wynne, Clive D.L.; Ostrander, Elaine A.; Sinsheimer, Janet S.; Udell, Monique A.R. (1 July 2017). "Structural variants in genes associated with human Williams-Beuren syndrome underlie stereotypical hypersociability in domestic dogs". Science Advances. 3 (7): e1700398. Bibcode:2017SciA....3E0398V. doi:10.1126/sciadv.1700398. PMC 5517105. PMID 28776031.
Where the domestication of the dog took place remains debated, with the most plausible proposals spanning Western Europe, Central Asia and East Asia. 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. This proposal is also debated.
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