The scientists travelled hundreds of kilometres along the ancient Chinese rivers, looking for dogs. With 27 million pet pooches in China, finding one wasn't hard.
But the scientists weren't after kennel club champions or paragons of obedience. They wanted dogs with history, the kind hidden in their genes.
On two separate expeditions along the Pearl and Yangtze Rivers, the scientists gathered thousands of canine cheek swabs, searching for animals that might settle one of the most burning questions in science today: Where did people and pooches first learn to co-exist?
Man's best friend has become a scientist's best muse.
The advent of inexpensive and highly accurate DNA sequencing has opened a new window into the past, giving researchers the ability to sift through billions of genetic markers for clues as to the origin of the first domesticated animal.
They have come to wildly disparate conclusions.
In recent years, journals have published papers trumpeting Central Asia, Europe and the Middle East as the birthplace of the domestic dog, the place where the wolf lay down next to a human – and, over the course of many years, got back up as the first domesticated animal.
Now, Chinese researchers are staking their own ground: The dog, they say, originated in what is now China and they're making a massive effort to prove it.
The dogs whose genetics they have sought aren't any proper breed. They are identifiable by their round heads; short and hard hair; Husky-sized bodies; and, usually, light yellow coats. Scientists simply called them "Chinese indigenous dogs," a name that hints at their long history. These animals could be the modern descendants of the first-ever dogs.
That, at least, is the argument by the Chinese scientists, who have recently made their own entries into a field where the stakes are scientific prestige – and a hint of national pride. Last year, Wang Guo-Dong, an associate professor at the Kunming Institute of Zoology, led a group that published research asserting dogs emerged first in what is now China 33,000 years ago, before travelling to the Middle East and Africa, on to Europe and then back, in some instances, to northern China. It is what the paper's authors called "an extraordinary journey that the domestic dog has travelled on earth."
In the past month, Prof. Wang has also led the Chinese effort to parry other theories. After an American-led group of scientists pointed to Central Asia as a likely origination point, Prof. Wang and his group wrote a response paper saying the American "conclusions may require revision" and that "the available data suggest southern China rather than Central Asia or Nepal" as the place where dogs emerged.
The American group, led by Cornell University researcher Laura Shannon, then fired back, suggesting the Chinese researchers had misunderstood the original findings and warning about data sourced from poor techniques that could lead to "spurious conclusions and should be interpreted with great caution."
Couched in the arch scientific language, it was not far from trading punches. At stake is the "pride of the scientist to be the first to find the origin of the dog. That's why there's been so many different claims," said Peter Savolainen, an associate professor at KTH Royal Institute of Technology in Stockholm and a co-author with Prof. Wang.
"Scientists are human, so wishful thinking occurs. And it gives publications in the best scientific journals, which is very good for your career. So, I think many articles have not been entirely objective."
The scholarly fisticuffs have yet to conclude. In the next few weeks, at least two more major papers will be published looking at canine origins. In June, Chinese researchers will hold a conference in which they hope people with records of 10,000 different dog genomes will come together and "a much clearer picture of dog origins" will emerge, Prof. Wang said.
"We will try to solve the problem."
One solution lies in a detailed comparison of the genomes of modern dogs. Scientists are looking for a diversity of genetic markers. The greater the number of such markers, the greater the likelihood that dogs originated from that place.
That's one tool. Another is to find really old dogs, carefully examining the genetics still intact from fossils many millennia old, offering a portal to a time much nearer. In China, that work has yet to begin; Chinese researchers recently travelled to Oxford University for training on the extraction of DNA from fossils.
"In my opinion, one needs to analyze DNA from ancient dogs to resolve this question," Love Dalen, a professor of evolutionary genetics at the Swedish Museum of Natural History, said.
The modern quest to find the first dog owes everything to technology. Ten years ago, it cost scientists a few dollars to sample a single genetic base pair. Today, they pay $10 to sample 200 entire genomes, with three billion base pairs each – and they are routinely sequencing genomes from dogs 5,000 years old. Vast quantities of new information are suddenly emerging.
"If you had said we could do this even five years ago I would not have believed you," said Greger Larson, who directs the Palaeogenomics & Bio-Archaeology Research Network at the University of Oxford, and who has spent years working on a "deciphering dog domestication" project.
People love dogs and tend to be curious about what they love.
But there are other reasons to pursue the history of the dog – an animal many scientists believe effectively domesticated itself, with friendly wolves adapting to humans in such a way that, over generations, a new tame species was born. "Knowing where and when dog were domesticated could offer considerable insights" into the actors and locations involved in "a process that may have been pivotal for setting the stage for the advancement of human civilizations in the Neolithic [age]," Adam Boyko, who is part of the Cornell University dog research team, said.
The story of the dog, too, reflects the story of humans. The two species have even evolved together. The same gene believed responsible for high-altitude adaptation among Tibetan people is present among Tibetan mastiffs.
But as the first animal to be domesticated, the dog also helped to change the course of history. The wolf's path to household companion blazed a trail for the domestication of other animals and fundamentally altered human connection with the natural world. Because the domestication of the dog was not merely the advent of the first pet. It created a new recognition that what was wild could become tame. "Which means, several thousand years later, we can now go out and intentionally domesticate something," Prof. Larson said.
But there's another question, too. Wolves appear to have become dogs about 15,000 years ago. That "just doesn't make any sense," Prof. Larson said, when you consider that humans and wolves co-existed for hundreds of thousands of years.
Then something happened: "A weird thing. Why is that happening? Where is that happening? What does that tell us?"
Sorting out those questions may take time. Prof. Larson speculates it could relate to humans moving into more northerly latitudes, placing more people in wolf territory.
As for the origin of the dog, his research suggests there may have been two domestication events, one in Europe, another in southeast Asia. Whatever the case, he does not expect that question to linger long. So many people are now chasing a question with such remarkable technology, he said, that a settled answer should emerge soon. "My hope right now," he said, "is that within a year, we'll know this stuff."
With a report from Yu Mei