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The love affair between humans and dogs has been going on for thousands of years. But when and where dogs first branched off from wolves is a source of scientific debate.
Over the past decade, various groups have posited different locations as the birthplace of the dog, including Europe and the Middle East.
Now, an international group of researchers presents another possibility.
After analyzing the whole genome sequences of 58 wolves and dogs from around the world, they say dogs first split from their wolf ancestors about 33,000 years ago in the southern part of East Asia.
The team also reports dogs began to migrate out of that part of the world across Eurasia 15,000 years ago, eventually making their way to Europe about 10,000 years ago.
The findings were published Tuesday in the journal Cell Research.
Peter Savolainen, an evolutionary geneticist at the Royal Institute of Technology in Solna, Sweden, and co-author of the paper, has spent the past 15 years studying dog DNA, trying to discern the canine's journey from aggressive and fearsome wolf to man's best friend.
The archaeological record is too sparse in many parts of the world to paint a complete picture of this evolution, he said, so DNA analysis may be the best way to sort it out.
In 2002, Savolainen and his colleagues looked at mitochondrial DNA from 654 dogs from around the world. They found dogs from East Asia had more genetic diversity than those from other global regions.
Another study from the same group in 2009 further narrowed this glut of genetic diversity to dogs from the area around southern China, northern Thailand, Vietnam and Laos -- what researchers call "southern East Asia."
It turns out genetic diversity is exactly what you would expect to find in a species' place of origin, Savolainen said. That's because as animals migrate, they take a limited amount of genetic information with them.
For example, if the original dog population started with 10 DNA types, it is unlikely the few individuals who left home would bring all 10 types with them. After all, most of the population likely stays put. More probable is some fraction of the DNA types would travel to Europe, and perhaps another fraction would land in Africa.
In the more recent study, Savolainen and his team examined where canine genetic diversity was highest, but this time they analyzed the whole genome sequence of 46 dogs and 12 grey wolves from across the planet.
Whole genome sequences are much larger and more complex than what is found in mitochondrial DNA. Therefore, the researchers say, it can provide a more holistic approach to understanding the evolution of dogs.
Once again, the data analysis suggested the same place of origin of dogs. Dogs from southern East Asia had more genetic information in common with wolves than with dogs from any other region in the world. They also had the largest genetic diversity.
"We find that dogs from southern East Asia have the same DNA types that are found in dogs all over the world, but also unique types that we don't see anywhere else," Savolainen said. "We saw that in the mitochondrial DNA, and now we see it in the genomic DNA as well."
To determine when dogs first diverged from wolves, the researchers compared the genes of grey wolves and southern East Asian dogs. After calculating how long it takes a certain number of mutations to appear in the genome, they concluded the split happened approximately 33,000 years ago.
That does not mean dogs became domesticated 33,000 years ago, however. And it's possible all dogs descended from a single group of wolves that split from other members of the species at that time.
For the paper, researchers studied dogs that represented historic populations of where they lived. That included breeds long associated with specific geographical locations, such as the Afghan hound (Central Asia), the Sloughi (North Africa), the Alaskan malamute and the Siberian husky (Arctic and Siberia) and the chihuahua (the Americas).
In southern East Asia, researchers looked for dogs in remote regions whose ancestors would have had little opportunity to breed with animals from other parts of the world.
"We think this works pretty well because if we go to the Chinese countryside and sample dogs from there, we find basically the same results in the Chinese chow chow," Savolainen said.
The DNA from these geographically diverse dogs also suggests how our canine companions moved around. For example, dogs that are more genetically similar to the southern East Asian dogs are likely older breeds and have been established in their homeland longer.
Although Savolainen feels confident in the results of his study, he said his team still has more work to do to understand the natural history of dogs.
The group already is working on extensively studying dogs from the southern East Asia region to find the exact birthplace of domesticated canines.
-- Los Angeles Times