Wednesday, 23 May 2012

The origin of domestic dogs.

Dogs are our oldest domestic animal, and the only one which predates the adoption of agriculture. This has led to a great deal of study of the origin of domestic dogs over the years. Despite this we are still not entirely sure where dogs were first domesticated. We are now confident that domestic dogs are descended from a single species of wild canid, the Grey Wolf (Canis lupus), and that domestic dogs were widespread across Eurasia by 12 000 years ago. The earliest dogs in the archaeological record are debatable; archaeological sites in Europe and Siberia contain several purported examples of domestic dogs dating back as far as 33 000 years ago, but it is hard to be confident that these were truly domesticated dogs and not just wolves foraging around human occupation sites. The widespread human habit of ritually burying dogs is generally taken as evidence of domestication; the oldest known ritual burial of a dog is from a site in the Czech Republic thought to be at least 26 000 years old. Attempts to date the domestication of dogs using molecular clocks (measuring the rate of DNA mutation and comparing it to the nearest known relative) have been inconclusive. One such study suggested dogs may have divered from wolves 135 000 years ago, but this is widely disputed.

Fossil dog skull from the Czech Republic, thought to be at least 26 000 years old. A mammoth bone has been placed in the dog's mouth, suggesting a ritual burial. Mietje Germonpr√©/Discovery News.

In a paper published in the Proceedings of the National Academy of Sciences on 21 May 2012, a team of scientists led by Greger Larson of the Department of Archaeology at the University of Durham publish the results of a new genetic study of the domestication of dogs, combined with a review of our current understanding of the subject.

The team studied the genetics of six dog breeds widely considered to be ancient, the Akita, the Basenj, the Eurasier, the Finnish Spitz, the Saluki and the Shar-Pei, and also looked at data from studies of ten other breeds considered ancient; the Afghan Hound, the Alaskan Malamute, the American Eskimo, the Canaan, the Chow Chow, the Dingo, the New Guinea Singing Dog, the Samoyed, the Shiba Inu and the Siberian Husky. 

Two of these dogs (the Eurasier and the American Eskimo are known to be twentieth century attempts to recreate ancient dogs; they should not show any notable differentiation from the general dog population. In the event the Eurasier did appear superficially to be ancient, but it is known to have been created by the hybridization of three ancient breeds, the Chow Chow, the Keeshond and the Samoyed, so this is not greatly surprising. 

The (African) Basenji, the Dingo and the New Guinea Singing Dog all originate from outside the range of the Grey Wolf, so these are highly unlikely to be ancient breeds, though they should show signs of long isolation from other breeds. In the event the Basenji did appear to be distinctive from other dogs, appearing ancient, whereas the Dingo and the New Guinea Singing Dogs appeared to have interbred with European dogs extensively in the recent past.

The Basenji; a dog breed from Central Africa which has largely escaped hybridization with European dogs. Dog Family.

The Alaskan Marmalute is the only other breed from outside Eurasia, being descended from ancient sled dogs used by Alaskan nomads, but this dog is known to have nearly become extinct in the twentieth century and been recreated by breeders. Unsurprisingly these did not appear to be ancient in the study.

The dogs that did appear to be ancient in origin were the Chinese Shar-Pei, the Japanese Akita, the Basenj, the North African Saluki, the Afghan Hound, the Eurasier and the Finnish Spitz. The Finnish Spitz is known to have nearly gone extinct in the 1880s, but to have been saved by the efforts of a breeder, Hugo Roos, who travelled to remote villages seeking out individuals that had not been hybridized with other dogs. All the other breeds are non-European, and appear to have had some degree of protection from hybridization with European dogs. None of them are from areas associated with ancient dog burials.

Interestingly several other Asian breeds, including the Tibetan Terrier and the Pekingese, appeared to be nearly as ancient, judged by their genetic isolation from other breeds. Larson et al. suggest that this may help to explain these results. Until the mid-nineteenth century European dog-breeders were little concerned with bloodline purity, so dogs from different breeds often hybridized. During this period Europeans expanded aggressively around the world, taking their dogs with them. Dogs are most likely to have first been domesticated in Europe or an adjacent area of Western Asia, but dogs from these areas have never been reproductively isolated. Genetic studies looking for 'ancient' breeds of dog are in fact looking for breeds that have been reproductively isolated for long periods of time, but the breeds this have achieved that are not particularly likely to be any closer to the original domestic dogs than those which have repeatedly hybridized with other breeds.

The Pekingese; not thought to be an ancient breed, but reproductively isolated for a long time. Dog Breed Info Center.

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