Purebred Dog Breeds into the Twenty-First Century: Achieving Genetic Health for Our DogsWhat is a breed? To put the question more precisely, what are the necessary conditions that enable us to say with conviction, "this group of animals constitutes a distinct breed?"
by Dr. Jeffrey Bragg
What is a Canine Breed?
In the cynological world, three separate approaches combine to constitute canine breeds. Dogs are distinguished first by ancestry, all of the individuals descending from a particular founder group (and only from that group) being designated as a breed. Next they are distinguished by purpose or utility, some breeds existing for the purpose of hunting particular kinds of game,others for the performance of particular tasks in cooperation with their human masters, while yet others owe their existence simply to humankind's desire for animal companionship. Finally dogs are distinguished by typology, breed standards (whether written or unwritten) being used to describe and to recognize dogs of specific size, physical build, general appearance, shape of head, style of ears and tail, etc., which are said to be of the same breed owing to their similarity in the foregoing respects.
The preceding statements are both obvious and known to all breeders and fanciers of the canine species. Nevertheless a correct and full understanding of these simple truisms is vital to the proper functioning of the entire canine fancy and to the health and well being of the animals which are the object of that fancy. It is my purpose in this brief to elucidate the interrelationship of the above three approaches, to demonstrate how distortions and misunderstandings of that interrelationship now threaten the health of all of our dogs and the very existence of the various canine breeds, and to propose reforms which will restore both balanced breed identity and genetic health to CKC breeds.
In order for canine breeds to fulfill their destinies effectively, the three distinct axes along which breeds are distinguished must have equal importance and consideration, otherwise serious problems arise. Breeds cannot be distinguished by ancestry alone, by purpose alone, or by typology alone. Unless these three vectors of breed identity interrelate fully and cooperatively, the fullness of that identity is missing or marred. Unfortunately, this full and cooperative interrelationship is a rarity in our contemporary dog world. The criteria of ancestry are applied rigidly and mechanically; the criteria of purpose and utility are subordinated or not considered at all; the criteria of typology are applied in a highly exaggerated, obsessive fashion. The interaction of the three approaches is seldom considered and almost never is a sustained effort made at the integration of the three.
Canine breeds come into existence in many different ways and their beginnings are very often shrouded in obscurity. Let it not be thought that the three or four hundred-odd dog breeds now extant are the only ones possible, or that there cannot be any more truly new breeds. Such is the genetic plasticity of the dog that there is no end to the possible unique variations of which the species is capable. New breeds are born and old breeds die periodically. The genetic transformation of the dog goes on ceaselessly, and for that reason it is impossible that any breed should remain frozen, with all its characteristics fixed and unchanging, for any appreciable length of time. It must be realized that canine breeds are manmade, created by artificial election out of the endless diversity of the canine gene pool. Breeds must not be confused with species or even subspecies, which occur naturally under the influence of natural selection; dog breeds are only unstable manmade varieties which would not survive unchanged in the natural world without human management.
An important characteristic of breeds is that they are created by breeders -- not by registries or protective organizations such as The Canadian Kennel Club. The origin and course of a canine breed is in the hands of its breeders, first, last and always. It is the business of cynological associations to facilitate and support the work of dog breeders and not vice versa. The purposes of the Animal Pedigree Act, under which CKC is incorporated, are the promotion of breed improvement and the protection of those who breed and purchase animals; such is the mandate of the Act and therefore of the Club [Animal Pedigree Act, §3(a,b)]. All else is secondary.
Ordinarily a breed has already existed for an appreciable length of time before it reaches the point of becoming a recognized breed served by a registry. Nonetheless, the event of its "recognition" by a registry such as CKC is always a crucial one in the history of a breed. As things now stand, breed recognition is far more crucial (and ultimately damaging to the welfare of the animals) than it need be or ought to be, but more of that anon. First let us examine what is needed to start a new and unique canine breed.
Four essential characteristics usually distinguish the origin in the genetic sense of a new breed (as opposed to the discovery, popularization and "recognition" of, for example, an autochthonous breed which may have existed in a particular region for a long time without connection to formal cynological structures). The first and most crucial characteristic is the founder event in which a finite number of individual canines is chosen to contribute genetic material to found a new and unique canine population. They may all be quite similar, or they may be widely divergent one from another (as when Bulldog and Mastiff specimens were used to create the Bullmastiff breed). What matters is that a finite and sometimes quite small number of individuals are selected from the existing canine population and set apart so that their genetic material alone forms the gene pool for the new breed. That is in fact the next characteristic: isolation. If the founder group continues to exchange genetic material at random with the general canine population, a new breed will not result. Without genetic isolation of the new founder group, the differentiation that creates a new breed cannot take place. The logical consequence of this isolation is the next characteristic: inbreeding. If the founder group is of small or moderate size, such inbreeding cannot help but occur. Even if the founder group should be quite large, ordinarily those who guide the breeding which creates the new breed will find it necessary at some stage to employ a strong degree of incest breeding or inbreeding, to facilitate the weeding-out of undesired characteristics and the fixation of desired traits. Particularly if individuals of widely divergent type and physique are involved, inbreeding will be required to set up a stable genome in which random variability is kept within limits defined by the breeders. The final essential factor is artificial selection, since inbreeding alone will not serve to fix type characteristics and to eliminate unwanted traits. The breeders must select among the individuals produced in early generations so that only hose displaying the desired characteristics are allowed to produce subsequent generations. Without the four factors of the founder event, isolation, inbreeding and artificial selection, new breeds ordinarily do not come into existence. These four tools are used to define a new genome which, hopefully, contains only the traits desired by the creators of the new breed and is able to reproduce itself, with its distinguishing characteristics, to a fair degree of stability and consistency.
Purebred dogdom is even now in serious trouble through a general failure to distinguish between what is necessary to establish a breed and what is desirable to continue that breed in perpetuity. Most registered breeds are less than a century old as registered breeds; many are but fifty or sixty years old. Yet nearly all breeds now show levels of expression of genetic defects that must be considered unacceptable. Over 500 distinct genetic defects have been cataloged in various breeds of purebred dogs and more continue to come to light regularly. Some of these have reached very high levels of incidence, creating problems for breeders and dog owners, threatening the health of entire breed populations. What is worse, in many instances organized control programs seem relatively ineffective. Although such programs successfully identify affected animals, in some cases individuals with several generations of "clear" ancestry stubbornly continue to produce affected stock. Let us try to examine what has gone wrong and what must be done to correct the situation.
First of all it must be recognized that practices which were essential for the differentiation and establishment of a new breed may not necessarily be desirable for its continuation over time and may in fact be prejudicial to a breeds continued existence over the long term.
Let us take isolation, for example. Without genetic isolation, it would not be possible to control the genome of a new breed still few in number. It takes time and careful breeding to fix a new combination of characteristics; while that is being done, the regular addition of new genetic material would generally be counterproductive. Yet in the long term, if genetic isolation is maintained, it will necessarily lead to degeneration through genetic drift. Similarly inbreeding, if it continues to be practiced after the need for it is past, will lead to a steadily increasing state of homozygosity which may well destroy the genetic health of the new breed. Even artificial selection, if carried on too strongly for too long, can combine with isolation and inbreeding to reduce drastically the effective breeding population, thus eroding the genetic health of the breed.
The present structure of The Canadian Kennel Clubs studbook registry (and others like it) embodies a fallacy which is directly responsible for the current genetic crisis in purebred dogs: the fallacy of breed purity. The ideal of the purified lineage is seen as an end in itself; accordingly, the studbook has been structured to reflect and to enforce that ideal rigidly and absolutely. 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; this same ideal, pushed to an illogical conclusion on the human plane, resulted in the now discredited "scientific racism" of the Nazis, who tried through selective human matings to breed an Aryan superman. 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. There is no support for this kind of racism in the findings of modern genetics -- in fact, quite the opposite: population groups that are numerically limited and closed to new genetic inflow are now thought practically certain to be genetically inferior. Certainly towards the close of the nineteenth century it became embarrassingly obvious that the human aristocracies of Europe were degenerating rapidly under their own version of the "closed studbook."
The ideal of breed purity as applied to purebred dogs has resulted at the end of the twentieth century in a subculture that holds "purebred" registered animal stock to be qualitatively superior to crossbred or "mongrel" stock. (The word "mongrel" is in fact part of the vocabulary of racism, being applied equally to canine stock of no recognizable breed, to animal crossbreeds and to persons of mixed race!) In this subculture -- presided over in Canada by the CKC -- it is thought to be of paramount importance that purebred stock be maintained unsullied by any genetic influence external to the supposedly superior strains that are produced by registered breeding in a closed studbook from a small group of foundation stock. New members of the CKC are required to subscribe to "Conditions of Membership" whereby they promise to have nothing to do with "dogs which are not purebred" (with the exception of family pets and boarders), "purebred" being specifically defined as referring only to dogs "registered individually or eligible for registration in records of the CKC." Litters which are made the subject of complaints that they may not be purebred are investigated and in many cases ceremoniously withdrawn from the registry by resolution of the Clubs Board of Directors. Whether you like the word or not, this is effectively a special variety of racism in concept and in practice.
Not all dog breeders are in agreement with the proposition that breed purity is more important than anything else, particularly when they are confronted with the problem of breeding dogs to demanding performance standards. Mostly such dissenters are obliged to carry on their breeding without the benefit of centralized pedigree record keeping and official certificates of registration -- for example, those who breed "Alaskan huskies", the high-performance racing sled-dogs that dominate both short and long distance dogsled racing, keep pedigree records and maintain sophisticated breeding programs, but only as individual breeders. Yet sometimes even participants in established purebred registries engage in a subtle kind of rebellion, quietly breeding according to their own judgment in defiance of formal restrictions. Thus the Racing Greyhound Club of Australia, when it recently subjected a broad sample of stock from its registry to DNA testing, is rumored to have discovered that many pedigrees failed to match DNA ancestry findings and that considerable interbreed crossing had apparently occurred. Similarly most Siberian Husky fanciers are aware that some CKC bloodlines may have received surreptitious infusions of genetic material from non-purebreds or from other breeds. In some circles one even gets the distinct impression that "its OK to crossbreed occasionally if you have a good reason for doing it and you manage it in such a way that no embarrassingly obvious mongrels are produced" -- i.e., "just don't get caught!" Thus the sanctity of breed purity may sometimes be less than inviolate in actual practice.
Population geneticists insist that limited populations under strong artificial selection, subjected to high levels of incest breeding - such as our own CKC purebreds -- simply cannot maintain genetic viability and vigor in the long term without the periodic introduction of new and unrelated genetic material. They are referring, moreover, to true outcrossing, the introduction of stock unrelated to the breeding line, not merely the use of a dog which might be from someone else's kennel but is derived from exactly the same foundation stock some generations back.
16-02-2008 om 00:00
geschreven door Jantie