Deciphering the dog family tree. The research results go beyond the interest of dog lovers - they can be used to overcome genetic diseases in humans
(Published in "Globes" on June 23-22, 2004 and quoted with the permission of the author)
The scientific journal "Science" reports on the completion of mapping the origins of the domestic dog. A group of researchers from Seattle, led by Professor Elaine Ostrander, compared the DNA sequences of 414 dogs from 85 breeds. They discovered a fascinating genealogy that illuminates the definition of dog breeds according to their closeness to the prehistoric wolf and the genetic expression of their shape and behavior. In fact, until the publication of this study, there was no comprehensive or accepted method for sorting the dogs. The DNA sequence comparison methods developed in recent years are the most accurate and reliable in the science of phylogenesis (the study of the history of races). The recently published studies on the origins of the Jewish people were carried out using these methods.
Darwin is interested
The research team sought to decipher the dog family tree due to the unusual circumstances of the dog's development as a domesticated animal. The relationship between man and his best friend began about 12 to 14 thousand years ago, when man discovered that he could use the sense of smell of wolf packs to locate hunting tracks. The dog was the first animal domesticated by man, still being a hunter-gatherer and living in caves. The domestication of sheep and cattle was much later and began only after the development of agriculture about 10,000 years ago. In the symbiosis (mutual dependence) between the wolf and man - the wolves helped man locate his prey and in return received their food from humans. In the process of domestication, a group of wolves was separated from their brothers in the wild and kept in captivity, this group became the nucleus from which the domesticated species developed - the dog. Since man is the one who managed the breeding of the dogs, he was able to find out over time the qualities he desired such as size, calm behavior or achievements in exploration tasks. Man mated the dogs with the desired traits and produced offspring for them, while the dogs with the undesirable traits were used for food. At the same time, the opposite process of leaving traits that would not survive in the wild, such as small fangs or fur colors that are not camouflage colors, took place.
In addition to domesticating dogs for hunting purposes, dogs were domesticated for grazing, guarding and patrolling, cargo, and rescue. In ancient Rome, man began to domesticate dogs also for entertainment purposes. In this process, different breeds of dogs were developed: tiny, big-eyed and long-furred, which were usually played by rich and bored ladies. The development of breeds of pet dogs continues to this day. Man actually replaced nature in the process of natural selection and directed with his own hands how the next generation of dogs will look and behave.
It is not for nothing that Charles Darwin devoted the first chapter of his book "The Origin of Species" to "Variation in Domestication Conditions". Darwin developed the idea of species variation in nature (evolution) based on the variation of domesticated animals. The many races of these animals, chief among them the pigeons and the dogs, were in his eyes the basis of the proof of the process of natural selection. "Who can believe that animals similar to sleds, bulldogs, or toy dogs, which are so different from all wild wolves, existed at the time under natural conditions?" Stupid Darwin. He came to the conclusion that the same intentional process done by humans in domesticated animals, occurs in nature during natural selection of environmental conditions. Many may be surprised to hear that Darwin developed the theory of evolution without even knowing the laws of heredity and genetics. "The Origin of Species" was published in 1859, while Gregor Mendel published the laws of heredity he discovered only in 1866.
The popular opinion before Professor Ostrander's research was carried out, was that the breeds were domesticated for hunting, their origin is earlier, while the toy dogs are the later. The research confirmed most of the assumptions but revealed a number of surprising findings: hunting dogs like the pharaoh, which is considered a descendant of the Egyptian dogs (statues and paintings of a similar dog were found in Egyptian tombs), were found to be modern, on the other hand, toy dogs like the Chinese chow-chow were found to be ancient.
Five major branches
The study indicated that the different breeds of dogs are divided into five branches. Four of the branches are of ancient breeds and the fifth is of all other dogs that are a more modern development of the domestication process. The oldest branch is that of the Asinian spitz dogs: the Shar Pei, the Shiba Inu, the Chow Chow and the Hakita. The Basanji dog belongs to the second branch. The third branch is the arctic spitz dogs: the Siberian husky and the Halsky malamute. The fourth of the Middle Eastern hunting dogs: the Afghani and the Saluki, while the other domestic dogs belong to the fifth branch for their completely different shape and behavior.
The grouping of all the other dogs in only one branch, led the researchers to continue the sorting with a more delicate technique of analyzing the DNA sequences. According to this technique, the fifth branch can be distinguished into three distinct groups:
- The Mastiff group includes the German shepherd, the Rottweiler and the Boxer.
- The herding dog group that includes, among other things, the greyhound and the Saint Bernard.
- The group of hunting dogs that includes, among other things, the pointer terrier and the retriever.
This distinction proves the genetic basis of dog behaviors.
The research results go beyond the interest of dog lovers, they can be used to overcome genetic diseases in humans. Since the pure races were hybridized among themselves, genetic defects were manifested among them that were hidden in hybrids from other races (for this very reason, "consanguineous marriages" are not recommended). This phenomenon is certainly not beneficial for the purebred dogs but positive for medical science. Heart disease, cancer, epilepsy and visual and hearing impairments also exist in dogs, sometimes even with a higher frequency. Cancer, for example, is quite common among boxers and pointers. Since purebreds have lineage records sometimes going back 20 and 30 generations, it is easier to locate these defective genes in their DNA sequences than in humans. Completing the identification of the defective genes that cause these diseases will be possible after the canine genome sequencing project is completed. The Massachusetts Institute of Technology (MIT) is engaged in this project, where the genome sequencing of the New York boxer dog "Tasha" is about to be completed. In July 2000, as I recall, the sequencing of the human genetic code was completed. The dog is the third mammal after man and the laboratory mouse to have its genetic code sequenced. After locating the defective genes in the pure breeds, all that is required is to reveal the corresponding DNA sequences in humans.
