Selective breeding


 * This article focuses on selective breeding in domesticated animals. For alternate uses, see artificial selection.

Selective breeding in domesticated animals is the process of developing a cultivated breed over time.

Purebreds
The very idea of 'breed purity' often strikes an unpleasant chord with modern animal fanciers because it is reminiscent of nineteenth-century eugenics notions of the "superior strain" which were supposedly exemplified by human aristocracies and thoroughbred horses. The application of theories of eugenics has had far-reaching consequences for human beings, and the observable phenomenon of hybrid vigor stands in sharp contrast.

The idea of the superior strain was that by "breeding the best to the best," employing sustained inbreeding and selection for "superior" qualities, one would develop a bloodline superior in every way to the unrefined, base stock which was the best that nature could produce. Naturally the purified line must then be preserved from dilution and debasement by base-born stock. This theory was never completely borne out. It can be said that when the ideal of the purified lineage or aesthetic type is seen as an end in itself, the breed suffers over time. The same issues are raised in the world of purebred cats.

Charles Darwin discussed how selective breeding had been successful in producing change over time in his book Origin of Species. The first chapter of the book discusses selective breeding and domestication of such animals as pigeons, dogs and cattle. Selective breeding is used as a springboard to introduce the theory of natural selection, and to support it.

Backyard breeding
The term backyard breeder is a general term used to describe people who allow their dogs or horses to procreate regardless of physical, genetic, and/or emotional health. While this term is often reserved for "home breeders", or those who breed for fun, it has also found recognition in the description of unreputable show and working breeders. The latter two groups often focus on one aspect of the dog (such as aesthetics), while ignoring the original function and temperament of the breed. In the process of careless breeding, many backyard breeders produce genetically weak animals that can be predisposed to debilitating physical deformities.

When such breeding is carried out on a large scale, the venue is called a puppy mill (especially in North America) or puppy farm. Because of the time and expense of feeding and caring for horses, which produce one foal per year, there are fewer horse breeders who produce animals en masse, though some individuals do engage in animal hoarding and breed far more animals than they can support.

Backyard breeding is popularly blamed for the proliferation of aggressive dogs for the sports of baiting and dog fighting. Dog fanciers generally believe that such ill-bred dogs are the reason for the bad reputation of some breeds in the public perception, and the resulting breed-specific legislation. In the horse world, overbreeding of grade animals that cannot be sold raises concerns that such animals will be slaughtered for horsemeat.

Scientific research
Selective breeding is also used in research to produce transgenic animals that breed true (i.e. they are homozygous) for the artificially inserted or deleted genes.

Breeding stock
A group of animals used for purpose of planned breeding.

When somebody is looking to breed animals, he is looking for certain valuable traits. For example, when one is looking to breed chicken, he intends to receive eggs, meat, or birds for further reproduction, on sturdy basis. He has to study different breeds and types of chicken and analyze what he can expect from a certain group of birds before he starts breeding them. Accordingly, he is looking to purchase the initial breeding stock, i.e. a group of birds that will the most closely fit his purpose. Initial group of birds is of certain value for him, because he is planning his project, based on specific traits of his breeding stock.