Tuesday, December 20, 2011

The Dog Is from Where?

An intellectual battle rages between researchers centered around the UCLA lab of evolutionary biologist Robert K. Wayne and the Royal Institute of Biology, Stockholm lab of Pier Savolainen for pinpointing in time and space the origin of the dog.  Savolainen and his colleagues place the first dogs in the ‘area south of the Yangtze River” not before 16,000 years ago.  Their findings are based on mitochondrial DNA studies, and the last few times out, they have engaged in all manner of mental contortions to keep their first dogs from breaking free of their geographic isolation. 
Wayne and his colleagues end up looking at the Middle East wolf with significant contributions from European and Chinese wolves, going back 40,000 or more years.  Their estimates are based on scans of the entire genome, especially of the nuclear DNA (from both parents, whereas mitochondrial DNA comes from the mother and the Y chromosome from the father.  
Now comes in PLoS One a study of the Y chromosome in wolves and dogs, including village dogs from the Middle East and the Area South of the Yangtze.   Sarah K. Brown of the University of California, Davis, author of the study, says the evidence points to three major patrilineal clades--in Africa, the Middle East, and the area south of the Yangtze, with the latter being the primary center of domestication, based on its higher levels of diversity.    Furthermore, she says that all European and modern North American breeds fall within that clade.  
A persistent bias in all these genetical analyses assumes that the highest genetic diversity is found at a point of origin; indeed, the statistical analysis the researchers use is based on that assumption.  Another built-in bias assumes that an expanding population radiated out evenly from the place of origin.
Both assumptions have been shown to be inaccurate, but they persist in part because statistically they must and in part because the results are what the researchers want to prove their point.    They do not.  
For all we currently know the founding dog population--or its descendants--could have been decimated by war, disease, or the influx of a few favored dogs--or masses of dogs.    Mitochondrial diversity can be increased by preferential keeping of breeding females for food production, as was apparently done in the Area South of the Yangtze River.  It can also increase through expansion of the dog population in an environment where it is relatively isolated from large-scale infusions of fresh blood that might overwhelm the native stock.  
If the dog was born on the move, we would initially expect a smallish population formed by inbreeding and outcrossing to other dogwolves and wild wolves--in other words breeding with what was available.  In How the Dog Became the Dog, I suggest that the important regions for that kind of mixing and matching were where various game and migration routes met, like the area of the Black and Caspian Seas and the Caucasus Mountains and the region of the Altai Mountains and Amur River headwaters.  A population of Middle Eastern dogwolves on the move with Homo sapiens from the area that is now the Persian Gulf passed through, even lingered in the former on its way to residence in the latter in the neighborhood of 30,000 to 40,000 years ago.    
As the ice sheets of the last glacial advance retreated the descendants of these people were on the move again--east, south and back to the west.  At least one of those movements would have brought dogs to the Area South of the Yangtze sometime after 16,000 years ago and probably closer to less than 10,000 years ago.  Impossible?  
A signal problem with the Area South of the Yangtze River is an apparent dearth of wolves and people, two essential ingredients in formation of the dog, until the dog appears 7,000 to 8,000 years ago, and it’s not for a lack of digging.  Another questions involves how dogs would exit the region in time to catch the great migration into the America’s beginning by many current estimates before 16,000 years ago, not to mention the rest of Asia and Europe.  
For now, it would be nice to see some village dog samples from northern China and Mongolia and more from the Carpathian Mountains and the Caspian and Caucasus region.

Read an excellent analysis at The Retriever, Dog, & Wildlife.