History of the Dog
The domestic dog is thought to have descended from the gray wolf, and has since evolved to become the most morphologically diverse mammalian species.
Phylogenetic tree representing the divergence of canine breeds from the wolf
The many breeds recognized today are the result of careful selective breeding for functional attributes deemed beneficial to their human owners including hunting, guarding, and herding and desirable physical characteristics such as skull shape, size, and coat variation.
The formation of breed clubs and the closure of their canine registries over the last few centuries have ensured that the breeds found today are purebred and share similar features as determined by the breed standards.
Genetic analyses across closely related breeds have suggested that a given breed represents a distinct genetic unit; consequently, relative genetic similarity within breeds makes the construction of definitive breed signatures a realistic proposition.