Humans
have maintained populations of useful animals around their places of habitat
since pre-historic times. Over these millennia, domesticated dogs have
developed into distinct types, or groups, such as livestock guardian dogs,
hunting dogs, and sighthounds. Artificial selection in dog breeding has
influenced behavior, shape, and size of dogs.
Some
researchers believe that the evolution of dogs from wolves is an example of
neoteny or paedomorphism selection, that results in aretention of juvenile physical
characteristics. Compared to wolves, many adult dog breeds retain such juvenile
characteristics as soft fuzzy fur, round torsos, large heads and eyes, ears
that hang down rather than stand erect, etc.; characteristics which are shared
by most juvenile mammals, and therefore generally elicit some degree of
protective and nurturing behavior cross-species from most adult mammals,
including humans, who term such characteristics "cute" or
"appealing". It has been seen that these traits can even prompt an
adult female wolf to act more defensively of dog puppies than of wolf puppies. The
example of canine neoteny goes even further, in that the various dog breeds are
differently neotenized according to the type of behavior that was selected.
Other researchers believe that because this comparison is based on the gray
wolf, which is not the ancestor of the dog, that this comparison is invalid.
Further research indicates that the concept of neoteny as a means of
distinguishing dogs from wolves is baseless.
To
maintain these distinctions, humans have intentionally mated dogs with certain
characteristics to encourage those characteristics in the offspring. Through
this process, hundreds of dog breeds have been developed. Initially, the
ownership of working and, later, purebred dogs, was a privilege of the wealthy.
Nowadays, many people can afford to buy a dog. Some breeders chose to breed
purebred dogs, while some prefer the birth of a litter of puppies to a dog
registry. It has been concluded that "findings imply that when selective
breeding was done by humans, it squashed the snouts of certain dog breeds, it
also morphed their brains" (Scientific American, 2010). Breeders have to
abide by the rules of the specific organization to participate in its breed
maintenance and development programs. The rules may apply to the health of the
dogs, such as joint x-rays, hip certifications, and eye examinations; to
working qualities, such as passing a special test or achieving at a trial; to
general conformation, such as evaluation of a dog by a breed expert.
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