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Starting points for reflectionson selection’s criteria A few excerpts from: “The truth about dogs” By Stephen Budiansky Ed. Penguin Books
“Anyone who owns or even comes into contact with dogs, which is to say everyone, should reads this scientifically grounded yet amusing compendium” - The Wall Street Journal –
============= Breeders aren’t opposed to making dogs that are good for something, it is just that that is not their job. Their job is to preserve a breed’s original purity and bring the breed up to a visual standard. Given the nature of dogs this is very hard, and takes intense concentration. Besides, pure breeders, like pure scientists, would lose face with their peers if they attempted something useful. - Raymond Coppinger, Fishing Dogs -
Inbreeding is basically cloning the old-fashioned way. All selective breeding is based on the obvious principle that you want to breed from individuals who have the traits you want, and cull the ones that don’t. The natural variation that exists in any population is the raw material that both the natural selection of evolution and the artificial selection of humans draw upon. < … omissis … > Breeding that dog to a close relative - a parent, or offspring, or sibling - increases the odds that the next generation will inherit whatever genes are responsible for those desirable traits. < … omissis … > Inbreeding is a way to get a desired trait into a very quickly and to make it appear consistently thereafter. The price, however, is that inbreeding does not discriminate between good traits and bad traits. It duplicates the good genes from a founding sire or dam; it also duplicates the bad genes. Alleles that cause defects, even fatal defects, generally get away with persisting at a low level in any population over time if they are recessive. A dominant allele that causes a fatal defect will get quickly weeded out because any animal that carries even a single copy of that allele will drop dead. But a recessive disease can be silently carried. Only an animal that has two copies of the recessive allele - that is, only an animal homozygous for that allele - will actually exhibit the disease. The problem with inbred animals is that inbreeding increases homozygosity al all gene sites, and increases homozygosity for recessive alleles just as it does for dominant alleles. Thus hidden recessive traits that may not have caused much trouble in the past are now brought together far more frequently. They become all the more of a problem if the disease is one that does not appear until late in life, such as cancer or some degenerative nerve disorders or progressive eye diseases. The genetic diseases that have been popping up in purebred dogs of late are unquestionably a result of this unmasking of once-latent problems. They are many, varied, and often very weird. Scottish terriers suffer from “Scottie cramp”, a nervous disorder in which the muscles of the back and legs go rigid, particularly when the dog is overexcited or engages in strenuous exercises. From an analysis of pedigrees it appears to be caused by a simple recessive trait. Epilepsy has been showing up in many breeds, notably poodles. Flat-coated retrievers have been suffering from an endemic of tumours. Deafness runs in Dalmatians and Australian cattle dogs. Collies, Norwegian elkhounds, cocker spaniels, Irish setter, and several other breeds are afflicted with retinal degeneration that leads to blindness. Boxers have a well-documented susceptibility to a defect that leads to congestive heart failure. Manchester terriers and poodles suffer from von Willerand’s disease, a haemophiliac disorder caused by a defect in blood-clotting factors. It is all rather like reading an account of the royal families of Europe after everyone had spent a few hundred years marrying their first cousins. < … omissis … > Less dramatically, but more insidiously, inbreeding leads to what is known as inbreeding depression. This is the accumulation of homozygous recessive alleles that have a cumulative, deleterious effect. These may not be anything so gory or dramatic as seizures or hemophilia; rather they are often small. Additive traits affect growth, vigour, and reproduction. In crossbred animals, these recessive traits may be masked by dominant alleles. But after several generations of inbreeding, the homozygosity in the genes that control these traits begin to take its toll. An inbreeding experiment in one research colony of beagles demonstrated a marked increase in the death rate of puppies born as inbreeding increased. About a quarter of puppies born to unrelated parents died. As the degree of inbreeding approached the point at which 50% of the genes for variable traits could be expected to be homozygous, the death rate increased to about a third of all puppies born; at homozygosities of up to 67%, half the puppies died; and at maximum of 78.5%, three-quarters died. All animals carry some deleterious recessive alleles, and some of these will be homozygous and thus expressed. But two unrelated individuals are unlikely to carry the same deleterious alleles at the same genes. Thus when two unrelated parents interbreed, the deleterious recessive alleles from one parent are likely to be cancelled out by a dominant gene from the other parent. This is what lies behind the phenomenon of hybrid vigour: offspring of two inbred but unrelated parents are highly heterozygous - that is, they have many genes of the kind “Bb”, where “B” is a dominant allele that covers up the effect of a deleterious recessive allele “b”. < … omissis … > Uniformity is obviously desirable, because it means offspring with predictable characteristics. But diversity is an inherent source of vigour and a protection against the unmasking of highly deleterious traits carried by recessive alleles. < … omissis … > A dog that wins a champion ribbon at a major show will be in great demand to sire litters of puppies left and right. And every time that happens, the genetic diversity of the next generation is dramatically narrowed. In a closed breeding population, such practices are a one-way process, driving diversity ever downward. There is simply no way to bring that lost diversity back into a closed gene pool. The point is that as the effective size and diversity of the breeding population is reduced, breeders are inbreeding whether they want to or not, and whether they know it or not. < … omissis … > There is no inherent reason one cannot breed for looks and healthiness or looks and good temperament simultaneously. But it requires striking a better balance between inbreeding and outbreeding than has been pursued by many to date. Of course humans generally respond to incentives, and the circular logic of the dog show and dog-breeding business has for a century now favoured precisely what has been happening. Looks are the easiest thing to change about a dog. They are the easiest thing to distinguish from one dog to another. People want dogs that win dogs shows because they win dog shows. There is a self-sealing circularity about it all, in which breed clubs establish highly arbitrary criteria for distinguishing a winning dog from a no winning dog (my Bernese mountain dog, thank God, has a few white hairs on the tip of his tail; if he did not, he would be a distinctly inferior specimen, according to the dog show judges), and then the same people who set the criteria breed the dogs that meet these criteria to people who want to meet the criteria. The development of breed standards in the late nineteenth century was an explicit attempt to give dog show judges a basis for awarding places. < … omissis … > Popular breeds like the collie were particularly prone to the tendency on the part of fanciers to “fabricate subtle points of distinction between animals and artificial models to measure them against”, the historian Harriet Rivto has written. In the 1890s, for example, came the craze for long, pointed noises, which had not been a characteristic of the breed before. From a scientific point of view, inbreeding is merely on tool, to be used to achieve a desired end: it is not an end in itself. But the establishment of closed breeding populations and registries of breeds by their very nature sets inbreeding up as something to be cultivated for its own sake. < … omissis … > It is easy to select for looks because looks are, well, looks: they are there for anyone to see. Also, many physical traits are well correlated with specific genes. Thus by choosing to breed from dogs that have certain desirable physical traits, we are actually choosing dogs with specific genes that really do directly influence those traits: a good physical trait really means that a good gene is behind it. But selecting based on outward appearance is still only an approximation; there is no perfect, one-to-one correspondence between what geneticists call the animal’s phenotype - the outward appearance - and the genotype, or the actual genes it carries. < … omissis … > There again is no inherent reason breeders cannot aim for pretty dogs that are also good-natured and healthy. But they first of all have to want to accomplish those goals. They also have to keep in mind that inbreeding in pursuit of any selection criteria, while a perfectly valid tool to fix in place the manifest virtues of an animal. Dog breeders could usefully take a page from modern breeders of purebred cattle and swine and other animals that are judged more by the bottom line of performance than by the circular dictates of fashion. These breeders have embraced the benefits of combining inbreeding to hone desired traits with outbreeding to cancel out the inevitable defects inherent in any one inbred line of purebred stock. Intelligent crossbreeding between breeds would be an even more efficient means of achieving this much-needed balance, but as long as the closed breeding books of registries like AKC hold sway, that is a lost cause.
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The Library Journal
American Scientist
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