What defines a breed? This is a big question these days, but there is a simple answer, whatever a cat fancy organization says it is!
 
 
    Seriously, the most essential feature of all pedigreed cat breeds that are on the showbench, or are in the process of being developed with an eye to the show bench, in all cat fancy associations is the breed standard. Historically, breeds were either discovered in a particular country, or as a found mutation, or created on purpose, but in all cases the breeders have bred for specific features that are considered desirable in the breed.
 

Natural populations may provide insight into how unique characteristics can arise and be maintained.

    A wide variety of forces cause the characteristics that result in a species or subspecies. These forces include:

1) natural selection, where those who compete successfully for food and shelter survive to reproduce, when many others die,

2) sexual selection where colors, display, song, or dance causes an individual to be selected by the opposite sex more frequently and therefore that individuals genes are passed along more than are those of others, and

3) genetic drift, where isolated, small populations lose some genes by random chance and fix in others and some mutations that a larger population would not.

    In the natural world those that survive are the ones who pass their genetic information on to the next generation. Elaborate methods of inbreeding avoidance lead to increased likelihood of survival of offspring, and the passing on of these behaviors.

    Pedigreed breeds do not come into existance in quite the same way as natural species though.  Instead, they are primarily man (or woman) -made through selective breeding.

About Selective breeding, or Artificial selection:

    People have been selectively breeding an assortment of animals to enhance various characteristics for hundreds of years. Long before we knew anything about genetics it was pretty clear that if you bred two animals with certain characteristics together, that their offspring might inherit those characteristics.

   To some extent humans even have done this themselves. A Viking who wanted to have strong sons might marry a strong woman. A woman who wanted to make sure her family was well provided for might select a loyal and reliable man who had good hunting skills - or is a good farmer  . A tribal leader who wanted to make sure that he produced many children might only marry a woman who had already borne a child, proving her fertility.

    In creating a breed of cats, or dogs, or corn, characteristic features are selected and bred for. This process is called "artificial selection". In artificial selection, as in natural selection, only a small percentage of the population reproduces. In this case those that reproduce are chosen to do so by humans. Individuals without the desired traits are not bred. Artificial selection can proceed at an astonishingly fast rate, because specific criteria are used to determine the parents of the next generation. However, this does NOT mean that other genetic forces don't occur. In fact some, like genetic drift, are a pervasive problem in man-made breeds.

     People, like most other mammals, have usually avoided mating with their close relatives. Incest is highly frowned on in most societies, and is illegal in many. Other mammals also have elaborate social behaviors to avoid inbreeding. There are powerful biological reasons for this, inbreeding causes a wide variety of health and fitness problems which reduce the likelihood of survival.

    Unfortunately, humans do not apply these same standards to the animals that we breed, particularly when we breed for appearance as opposed to performance.

    Why is this? It is because the easiest way to initially reproduce a physical characteristic is to ONLY breed those that have that characteristic. If only a few individuals have that characteristic, then you may be drastically limiting the "gene pool" of the breed. In addition, it is always easier to use the animals that you own, as opposed to buying more or looking for outside studs whose owners will allow you to use them. There are also problems in bring in new individuals or sending a girl out to a stud. New diseases may be brought in, undesirable traits may crop up unexpectedly in offspring. so, commonly only a very small number of animals is chosen to produce the next generation.

    What may have started as a matter of convenience may produce an animal of outstanding type. People want to repeat success. If it worked once, it may work again, so the breeding practices are continued.

    People who have used this method then train others to do the same thing, and the method gets passed form mentor to newcomer for generations. Certainly, when the gene pool becomes very small, variation is reduced, the offspring become very consistent in type.

    On the other hand, some breeders have had great success in breeding for "type" while avoiding inbreeding.  This generally leads to healthier, more vigorous, animals.  They in turn train others in their preferred method of breeding.  From the view of the genetic health of the breed, this should be the preferred method.  Unfortunately, old habits can be hard to break.

    What exactly is inbreeding?  How does it relate to line-breeding?  Why does it affect the health of the animal?

 

What is inbreeding?                (next)

 
 
 
 
 

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@Heather E. Lorimer, Ph.D.