Man's best friends may have started off as European gray wolves, according to scientists whose research is challenging earlier thinking around where and why dogs became domestic animals.
The finding, detailed in this week’s issue of the journal Science, challenges past research that had placed dog domestication in East Asia or the Middle East and that had linked the phenomena to the rise of agriculture.
“Other wild species were domesticated in association with the development of agriculture and then needed to exist in close proximity to humans. This would be a difficult position for a large, aggressive predator,” study co-author Robert Wayne, an evolutionary biologist at the University of California, Los Angeles, said in a statement.
In the new research, a team led by evolutionary geneticist Olaf Thalmann of Finland's University of Turku used DNA analysis techniques to determine the origins of the first tamed wolves.
The scientists collected DNA from 18 mostly European ancient canid samples, eight of which were classified as doglike and ten that were wolflike. They compared the ancient DNA to samples gathered from 77 dogs from a wide variety of breeds; 49 modern wolves from Europe, Asia, and elsewhere; and four coyotes.
From Scavenger to Protector
The researchers found that the DNA of modern dogs most closely matched that of ancient wolves from Europe, indicating that dog domestication began there. They also concluded that dogs are descended from a population of ancient European wolves that are now extinct.
"We found that instead of recent wolves being closest to domestic dogs, ancient European wolves were directly related to them," Wayne said.
"This brings the genetic record into agreement with the archaeological record. Europe is where the oldest dogs are found."
The dog fossils used in the study are dated to 19,000 to 32,000 years ago, around the time that hunter-gatherers were living in Europe.
Initially, wolves could have scavenged off the carcasses of wooly mammoths and other large megafauna that the human hunter-gatherers killed, Wayne told National Geographic.
As they became domesticated, Wayne says, tamed wolves could have returned the favor by protecting their masters against dangerous predators, or by helping with the hunt.
Once or Multiple Times?
Brian Hare, director of the Canine Cognition Center at Duke University, said the findings make sense based on what scientists know about early human migration. (Related: "Opinion: We Didn’t Domesticate Dogs. They Domesticated Us.")
"Humans and wolves would have first interacted as modern humans left Africa around 40–50,000 years ago and entered the Middle East and Europe," said Hare, who was not involved in the research.
Searching for Ancient DNA
It's unclear from the new study whether dog domestication began in one group of European hunter-gatherers and then spread or happened in multiple groups simultaneously.
"Both scenarios seem plausible," Thalmann said.
Adam Boyko, a computational biologist at Cornell University who has studied genetic diversity in dogs, said scientific evidence suggests that dogs were domesticated in a single part of the world, as opposed to it happening separately on various continents.
He said the new study makes a good case for that origin being in or near Europe.
Boyko added, however, that he is waiting to see if follow-up studies that use other genetic markers, particularly nuclear DNA, reach the same conclusion.
The study by Thalmann's group compared the mitochondrial DNA of the animals, which is abundant in ancient remains. Unlike nuclear DNA, which is found in the cell nucleus and inherited from both parents, mitochondrial DNA is passed down only through the maternal line, from mother to offspring.
UCLA’s Wayne said his team has tried and failed to gather nuclear DNA from ancient canine, but they are not giving up: “It is something we will do in the future.”
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