A new comparison of DNA from modern canines and ancient fossils suggests that today's pets are descended from now-extinct populations of wolves in Europe.
They likely scavenged bones from scrap piles left behind by hunter-gatherers, say researchers in today's issue of the journal Science.
And the bolder the animals got, the more food they took, and the more loyal they became to humans, they say, adding this process of domestication likely began as many as 19,000 to 32,000 years ago.
"All modern dogs have a very close relationship to ancient dogs or wolves from Europe," says lead author Dr Olaf Thalmann, from the University of Turku in Finland.
The team analysed the mitochondrial DNA of 18 prehistoric canines -- eight dogs and 10 wolves -- and compared this to DNA from a comprehensive panel of 49 wolves and 77 dogs, including Basenji and Dingo, three recently published Chinese indigenous dogs and four coyotes.
The ancient samples came from Russia, Ukraine, Central Europe, the United States and Argentina, says Thalmann. Some were more than 30,000 years old. The modern DNA from dogs and wolves spanned the globe, from Israel to China, Sweden to Mexico.
They researchers found that the modern dogs' DNA was most closely related to either ancient European canines or modern European wolves.
"The oldest domesticated dog material came from Europe," says co-author Robert Wayne, a professor in the department of ecology and evolutionary biology at the University of California Los Angeles.
"It was an inescapable conclusion."
However, other researchers say the matter of who tamed dogs first and where it happened is far from settled.
A separate team of researchers published a study in Science in 2002, saying that modern dogs came from southern China.
"Our data points to origins in China and I am still pretty sure that is the place," says Dr Peter Savolainen, an associate professor at the Royal Institute of Technology in Sweden.
Savolainen says the study by Thalmann and colleagues lacks samples from important parts of the world -- namely the Middle East and China.
"If you are looking for the origins of dogs and you only have samples from Europe, then of course it must be Europe," he says.
Savolainen says that much like the "Out of Africa" theory that says humans originated in Africa and migrated elsewhere, dog history follows an "Out of south China" scheme.
"You see several branches that are unique among dogs in south China and you don't see them anywhere else," he says.
Asked about the criticism from China theorists, Thalmann countered that his team used more complete DNA sequencing and older samples that show Europe was indeed the place where it all began.
Still, the matter is far from settled, says Thalmann. More research in the years to come may reveal more on the topic, perhaps through the discovery of more fossils, or a more complete look at the genetic data.
In the meantime, most experts agree that early dogs became a part of human life long before the development of agriculture and farming societies.
Little is known about the people who domesticated them, or how they did it.
But Savolainen believes that wolves took the lead when it came to befriending humans, at least initially.
"They approached human camps and ate from the scrap heaps and those who dared come closer would get most of the food and they would have an evolutionary advantage," he says.
"So with each generation they would sort of tame themselves to get accustomed to humans. That is everybody's favorite theory, and I think it is a nice theory as well."
As some wolves relied less on killing prey and more on eating scraps, their snouts gradually grew shorter. They likely followed human groups whenever they picked up and moved camps.
Then, about 10,000 to 15,000 years ago, the closer friendship truly began.
"At some point, people and wolves really started interacting and humans took over the rest of the domestication process," says Savolainen.
Thalmann says his team's evidence suggests dogs likely accompanied European explorers to the New World.
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