Where do dogs come from?
Grey wolves are their ancestors. Scientists are pretty consistent about that. And researchers have suggested that dogs' origins can be traced to Europe, Western Asia, Siberia and South China.
Central Asia is the newest and best candidate, according to a large study of dogs from around the world.
Cornell University scientists Laura Shannon and Adam Boyko, and an international group of other scientists, studied not only pure-bred dogs but also street or village dogs - the free-ranging scavengers that make up about 75 per cent of the planet's one billion dogs.
The most recent common ancestor of today's dogs lived in Central Asia, said Cornell University scientist Adam Boyko, although he added that he cannot rule out the possibility that some dogs could have been domesticated elsewhere, and died out.
Dr Shannon analysed three kinds of DNA drawn from more than 4,500 dogs of 161 breeds and 549 village dogs from 38 countries, Dr Boyko said - the first time this has been done for such a large and diverse group of dogs,
That allowed the researchers to determine which geographic groups of modern dogs were closest to ancestral populations genetically. And that led them to Central Asia as the place of origin for dogs, in much the same way that genetic studies have located the origin of modern humans in East Africa.
The analysis, Dr Boyko said, pointed to Central Asia, including Mongolia and Nepal, as the place where "all the dogs alive today" come from.
The data did not allow precise dating of the origin, he said, but showed it occurred at least 15,000 years ago.
They reported their findings on Monday at the Proceedings of the National Academy of Sciences.
Dr Greger Larson, from Oxford University, who is leading an international effort to analyse ancient DNA from fossilised bones, said he was impressed by the scope of the study.
"It's really great to see not just the sheer number of street dogs, but also the geographic breadth and the number of remote locations where the dogs were sampled," he said.
He also praised the sampling of different kinds of DNA and the analytic methods.
But in the world of dog studies, very little is definitive.
The most recent common ancestor of today's dogs lived in Central Asia, Dr Boyko said, although he added that he cannot rule out the possibility that some dogs could have been domesticated elsewhere, and died out.
Or dogs domesticated elsewhere could have gone to Central Asia from somewhere else, and then diversified into all the canines alive today, he said.
Dr Larson, who was not involved in the study, said he thought the Central Asia finding required further testing. He said he suspected that the origins of modern dogs were "extremely messy" and that no amount of sampling of living populations would be definitive. He also said a combination of studies of modern and ancient DNA was necessary.
Dr Boyko said the research for the first time studied three sources of DNA from pure-bred and village dogs worldwide. The team analysed DNA from all the chromosomes in the cell nucleus - from the Y chromosome specifically, found only in males - and from mitochondria, cellular energy machines outside the nucleus that are inherited from the mother.
Dr Boyko travelled to a number of the locations where blood was drawn from village dogs.
He said: "The great thing about working with dogs is that if you show up with food, you don't usually have trouble recruiting subjects. Usually.
"We showed up in Puerto Rico at a fishing village, and the dogs turned up their noses at roast beef sandwiches. They were used to eating fish entrails."
NEW YORK TIMES