Exactly where did man's best friend come from? Researchers disagree.
Every dog has its day, and now it’s a European wolf's turn.
A paper published in the journal Science on Thursday has offered a new answer to the much-tussled-over question about where dogs originated. The latest proposal – the third in just a decade – is that dogs emerged in Europe, out of a now-extinct line of gray wolves.
“We have to reconsider the origin of modern dogs,” says Olaf Thalmann, a geneticist at the University of Turku, in Finland, and a lead author on the paper, “and need to include Europe into the scenario.”
There is little disagreement that dogs are the descendants of gray wolves that befriended – or perhaps were befriended by – humans. That tale has been illustrated in world folklore centuries old. But just when and where that almost mythical pact between man and soon-to-be dogs happened is anything but agreed on.
And there are good reasons for that. The morphological data is not telling: early dogs resembled wolves; some modern dogs still do. And dogs, like humans, are adroit travellers; tracing them is difficult.
“Wolves and dogs are mobile and widespread,” said Carlos Driscoll, a researcher at the US National Cancer Institute who has published on cat domestication and who was not involved in the latest paper, in an email to the Monitor. “This makes assigning a geographic origin problematic because the 'source' population might not be living today where it did 10,000 years ago.”
Genetic data is also liable to tell different stories. In 2002, Peter Savolainen, of the Royal Institute of Technology in Sweden, reported in the journal Science that dog domestication had occurred in southern China about 15,000 years ago. His analysis of portions of mitochondrial DNA from modern dogs showed that the greatest genetic diversity in dogs was found in the region, suggesting that dogs had emerged there first.
Mitochondrial DNA, found outside the cell’s nucleus and in its mitochondria, is passed from a mother to both her male and female children. It is often used to trace maternal lineage in human populations, as well as in other animal species.
For years, sleeping dogs were let lie: the question appeared to be answered. But in 2010, Robert Wayne, of the University of California, Los Angeles, and his team reported in Nature that dogs had arisen first not in Asia, but in the Near East. The problem with the previous paper was that genetic diversity, while a reliable indicator of human origins in Africa, was less meaningful when applied to dogs, says Dr. Wayne, who is also a lead author on the newest paper. Too much migration, trade, and breeding had muddled the tale of how which genes got where and when, he says.
“There’s a lot of mixing by trade, and that kind of add mixture affects genetic diversity,” says Wayne.
Instead, Wayne and colleagues investigated how much the genetic signatures in the mitochondrial genomes of modern dogs matched those of modern wolves. The team discovered that dogs were a closest match to Israeli, Iranian, and Saudi Arabian wolves, a find that put the domestication of the dog at the same location as that of the cat: felines self-domesticated in the Near East about 12,000 years ago, as natural selection favored cats that warmed to humans and were rewarded for it with food.
But that conclusion soon went to the dogs. Subsequent research has shown that dogs and wolves have interbred in the Near East, making their close relationship a red herring in the hunt for dog origins, says Wayne. More research has also shown that dogs are related not to modern wolves, but to ancient, extinct ones, he says. Altogether, that means that modern wolf and dog genomes will not provide the answer to dog origins, he says.
“It was a little bit of a disappointment,” says Wayne.
So, Wayne partnered with Dr. Thalmann and others and returned to the question using not just modern genomes, but also ancient ones. The team analyzed the mitochondrial genomes of 18 prehistoric canids, including both wolflike dogs and doglike wolves, from Eurasia and the Americas and dating to about 36,000 to 1,000 years ago. These sequences were then compared to complete mitochondrial genome sequences from 49 modern wolves, 77 modern dogs, and four coyotes.
Next, all of the species were assembled into an evolutionary tree. That map showed that ancient European canids were grouped in each of the four clusters of modern dogs, suggesting that what we now call pets originated from extinct wolves in long ago Europe. The team then used molecular dating to put the point at which that happened sometime between 18,800 and 32,100 years ago.
The findings are consistent with the fossil record, since the oldest known dog specimens are from Stone Age Belgium and Russia, Wayne said.
“This places dogs firmly in hunter-gatherer culture,” says Wayne. “Those first proto-dogs began following humans around, taking advantage of human waste.”
The researchers have yet to analyze the DNA inside the nucleus from the ancient species but plan to investigate how well that genetic data confirms their results, says Thalmann.
“We were only able to draw conclusions using the mitochondrial genome,” he said, in an email to The Monitor. “It still is just the story of one locus. So investigating nuclear data from these fossils and perhaps other specimens would be a logical next step.”
Matthew Webster, a researcher at the Uppsala University, in Sweden who has published on dog evolution and who was not involved with this latest research, said that the paper makes a valuable contribution to the debate in including ancient specimens in the analysis.
Research “suggests that modern dog and wolf samples are not informative regarding dog origins and that we need to look at ancient canid samples,” he said. “This paper is a first step in that direction.”
Still, the paper’s findings are inconclusive without more data – namely, data from the Middle East and China, says Dr. Webster. Since the team could not retrieve genetic data from Middle Eastern samples, and could not obtain samples from East Asia, the research relies just on samples from Eurasia and the Americas to make its case for European dog origins, he said.
“There is still a possibility that additional samples from other proposed centres of origin (Middle East and China) could show a greater affinity with dogs than some of the European samples presented here,” he said, in an email to the Monitor.
That, says Dr. Savolainen, is the biggest problem with the new paper.
“This new research is problematic in design,” he says. “If you don’t have a sample from the correct region, you will get a false answer. You get the answer to the question you ask.”
His team is continuing their research to provide more evidence that southern China is, in fact, the original dog’s cradle, he said. His paper published this summer in Proceedings of the Royal Society B had buttressed his 2002 results, finding that some American dogs shared no genetic signatures with European dogs but did with Asian dogs.
“Southern China is still the strong candidate,” he says.