More than 3,000 years ago, in what is now Kazakhstan, six dogs were laid carefully in the ground. Were they beloved pets? Sacrifices, since they seem to have ritually arranged? No one can say for sure. But for scientists studying how dogs threaded themselves into human history, archaeological finds like these are precious. They provide a chance to peek into the DNA of dogs, to see just how they leapt from one group of humans to another, making their own migrations across continents.
Advances in sequencing ancient DNA have revealed that over millenia, people have moved into new regions in successive waves, sometimes intermingling with local folk, sometimes replacing them entirely. Researchers curious if the same was true for other creatures living alongside them turned to DNA from 17 dogs that lived in the last 10,000 years in Eurasia, including one from the burial in Kazakhstan. In a study published Nov. 13 in the journal Science, they reveal that dogs traveled with their humans into new lands, and sometimes, even if the human newcomers didn’t stick around, the dogs did.
Dogs have lived among humans for far longer than you might realize—before there were cities, before there were even farms, they were with us, says Laurent Frantz, a professor at the Ludwig Maximilian University of Munich and an author of the paper. Chickens, horses, pigs, sheep, goats, and cows are all more recent additions to humans’ menagerie than dogs. And these pooches seem to have been well-traveled, even millennia ago; previous work by Frantz and collaborators suggests dogs living in North America before the arrival of European colonists originally came from Eurasia, as humans did.
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But it can be surprisingly tricky to find their remains among the vast numbers of other animal bones humans leave behind. “I travel a lot with a colleague of mine that works on horses,” Frantz says. “We go together through boxes trying to find material coming from these sites, and we find sheep, sheep, sheep, sheep.” But dogs are more likely than other animals to have been buried specially, he says, in their own graves, with some care.
For their paper in Science, Frantz and his collaborators were curious about a pivotal moment in Asian history: the arrival of bronze in China. The technology to make the metal traveled from the western part of the continent to the east about 5,000 to 4,000 years ago, he says, and “it completely transformed society.” The people who brought bronze seem to have come with horses, cattle, and sheep. Did they also bring new types of dogs?
Using never-before-analyzed DNA from dogs living in Eurasia over the last 10,000 years, the team pieced together an intriguing picture. At first, before the Bronze Age, dogs in western and eastern Eurasia were distinct populations. Between the two, in a place called Botai in Kazakhstan, there were even dogs whose ancestors came from the Arctic, perhaps reflecting the cold local climate or the specific needs of the Botai people.
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But as the human migration linked to the spread of bronze crept eastward, genetics suggests the people of Botai mostly disappeared, subsumed by the newcomers. “It’s like the end of the world, in a way,” Frantz says. “Their way of life is gone, and a lot of their genetics also disappear.” The same was true of Botai’s dogs.
When bronze reached East Asia, something different happened: The locals picked up the newcomers’ bronze technology and their dogs, but they didn’t pick up their genes. “What’s really interesting with the dogs,” says Frantz, “is they seem to flow more like the technology than the people.”
That’s an apt comparison, says Audrey Lin, a paleogeneticist at the American Museum of Natural History who was not involved in the current study. “They are a technology,” she says.
While it’s impossible to know from DNA what dogs were up to with humans all those years ago, they were likely used for hunting, herding, or perhaps as a kind of alarm system once humans had turned in for the night. So it makes sense that they might have been traded.
Frantz is eager to explore how dogs spread through Southeast Asia, down into Australia. And he is curious, too, not just about the anthropological questions dogs can answer, but how they shaped themselves to live so long in tandem with humans. They traveled with hunter-gatherers, they were bred by the Romans, they lived on remote islands in Siberia—all long before there was easy exchange between these parts of the world.
“There are lots of questions that we have,” he says, “about dogs themselves.”
