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Selective breeding

A breed[?] or landrace develops over time as through selective breeding as the owners of the animals use three strategies to refine local populations. The Appaloosa horse, which was developed by the Nez Perce Indians in the Northwest United States can be used an example; The Spanish had established horse breeding in what is now New Mexico by about 1600, and the Spanish of that era were known to have horses with spotted coats. By 1806 (when they are mentioned in journals kept by the Lewis and Clark expedition) the Nez Perce had developed strong, hardy, spotted horses.

How did they do this?

  1. isolation. There must be a period in which the members of the group are relatively fixed, so that no new genetic material comes in. Without genetic isolation of the group, the differentiation that creates a new breed cannot take place.
  2. artificial selection. Breeders must prevent random mating from coming about, and limit mating to those individuals who exhibit desired characteristics. The logical consequence of this isolation is the next characteristic: inbreeding.
  3. inbreeding. Ordinarily those who are controlling the artificial breeding will find it necessary at some stage to employ a strong degree of linebreeding or inbreeding (mating closely related individuals), to facilitate the weeding-out of undesired characteristics and the fixation of desired traits. Inbreeding and linebreeding are controversial aspects of artificial selection, but have been practiced for centuries.

It is not known if the The Nez Perce practiced inbreeding, but they were reputed to geld stallions judged unsuitable for breeding, and to trade away mares likewise unsuitable for breeding, which accomplishes the goals of isolation and artificial selection.

Closed vs. open studbook

A studbook is the official registry of approved individuals of a given breed kept by a breed association. It is said to be "closed" if individuals can be added only if their parents were both registered. It is said to be "open" if individuals can be added without their parents being registered, such as by inspection.

Studbooks have been kept for centuries; the concept of the breed associations and clubs is more recent. Most of the "purebred horses" have open studbooks. For example, a "purebred" Arabian mare can be "examined" by the Trakehner authorities; if she is found acceptable, her offspring can be registered as Trakehner. in which mares and stallions

The Special Problem of Purebred Dogs in North America and The Fallacy of Breed Purity

Purebred dogs of breeds recognized by The American Kennel Club and The Canadian Kennel Clubs studbook registries are examples of "closed studbooks". In many modern dog breeds recognized by the Kennel Clubs, there are high incidence of specific genetic diseases and increased susceptibility to other diseases, reduced litter sizes, reduced lifespan, inability to conceive naturally, etc. This came about because:

  1. Many breeds have been established with too few founders or ones that are already too closely related, or both
  2. artificial isolation: the registries (stud books) are closed for most breeds; therefore you cannot introduce diversity from outside the existing population.
  3. Most selective breeding practices have the effect of reducing the diversity further. In addition, the wrong things are often selected for (i.e., the "most winning" sire being popular regardless of soundness.
  4. Even if the founders were sufficiently diverse genetically, almost no one knows how their genetic contributions are distributed among the present day population.
  5. Consequently, breeding is done without regard to conserving these contributions, which may be of value to the general health and survival of the breed.

The apparent "fallacy" of breed purity seems particularly strong in the dog-show[?] world, which is run primarily by the American and Canadian Kennel Clubs. The ideal of the purified lineage is seen as an end in itself. This insistence on absolute breed purity arises from nineteenth-century notions of the "superior strain" which were supposedly exemplified by human aristocracies and thoroughbred horses.

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.



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