More than 3,000 years ago, in what is now Kazakhstan, six dogs were carefully buried in the ground. Were they favorite pets? Sacrifice, since they seem to be ritually arranged? No one can say for sure. But for scientists studying how dogs entered human history, such archaeological finds are very valuable. They provide a glimpse into the DNA of dogs, to see how they jumped from one group of people to another, making their own migrations across continents.
Advances in ancient DNA sequencing have shown that, over thousands of years, people moved into new regions in successive waves, sometimes mixing with local populations and sometimes replacing them entirely. The researchers, curious whether the same was true for other creatures living around them, turned to the DNA of 17 dogs that lived over the past 10,000 years in Eurasia, including one buried in Kazakhstan. In a study published Nov. 13 in the journal Sciencethey show that dogs traveled with their people to new lands, and sometimes, even if the newly arrived people did not stay here, the dogs did.
Dogs have been around people for much longer than you might imagine: they were with us before there were cities, even before there were farms, says Laurent Franz, a professor at the Ludwig Maximilian University of Munich and author of the paper. Chickens, horses, pigs, sheep, goats and cows appeared in the human menagerie later than dogs. And these dogs seem to have traveled a lot, even thousands of years ago; previous Job Franz and his colleagues suggest that dogs that lived in North America before the arrival of European colonists originally came from Eurasia, like humans.
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But finding their remains among the vast amount of other animal bones left behind by humans can be surprisingly difficult. “I travel a lot with a colleague who works with horses,” says Franz. “We search the boxes together, trying to find material coming from these places, and we find sheep, sheep, sheep, sheep.” But dogs, he said, more often than other animals were buried on purpose, in their own graves, with a certain amount of care.
For my article in ScienceFranz and his collaborators were interested in a turning point in Asian history: the appearance of bronze in China. Metal technology spread from the western part of the continent to the east around 5,000 to 4,000 years ago and “completely changed society,” he said. The people who brought the bronze seem to have come with horses, cattle and sheep. Did they also bring new types of dogs?
Using previously unanalyzed DNA from dogs that lived in Eurasia over the past 10,000 years, the team pieced together an intriguing picture. At first, before the Bronze Age, dogs in Western and Eastern Eurasia were separate populations. In between, at a place called Botai in Kazakhstan, there were even dogs whose ancestors came from the Arctic, perhaps reflecting the cold local climate or the special needs of the Botai people.
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But as the human migration associated with the spread of Bronze moved east, genetics suggest that Botai's inhabitants largely disappeared, absorbed by newcomers. “In some ways it feels like the end of the world,” Franz says. “Their way of life is gone, and much of their genetics is disappearing as well.” The same thing happened with Botai's dogs.
When the bronze reached East Asia, something different happened: the locals adopted the bronze technology of the aliens and their dogs, but did not adopt their genes. “What’s really interesting about dogs,” says Franz, “is that they are more like technology than people.”
“It's a good comparison,” says Audrey Lin, a paleogeneticist at the American Museum of Natural History who was not involved in the current study. “They are technology,” she says.
While it is impossible to know from DNA what dogs did to humans many years ago, they were most likely used for hunting, herding, or perhaps as some sort of alarm system when humans went to bed. Therefore, it is quite logical that they could be sold.
Franz wants to know how dogs spread throughout Southeast Asia, all the way to Australia. And he's also curious not just about the anthropological questions dogs can answer, but also about how they shaped themselves to live for so long in tandem with humans. They traveled with hunter-gatherers, were bred by the Romans, and lived on the remote islands of Siberia – all long before there was easy trade between these parts of the world.
“We have a lot of questions,” he says, “about the dogs themselves.”
