Man's best friend gained that title in Europe, according to a new study that pinpoints the origin of dog domestication to between 18,800 and 32,100 years ago.
The study places the origin of dogs before the rise of agriculture, suggesting that human hunter-gatherers tamed the wolf. Whereas previous genetic studies had placed the origin of dogs in the Middle East or Asia, this research is the first to focus on the genetics of ancient dogs, rather than looking at modern dogs and trying to extrapolate back.
"All modern dogs analyzed in our study were closely related to either ancient dogs and wolves from Europe or modern wolves from there," study scientist Olaf Thalmann, a postdoctoral researcher at the University of Turku in Finland, told LiveScience in an email.
The beginning of dogs
Dogs are the only large carnivores that humans have ever domesticated, but when and where dangerous wolves became lovable pups has been hard to pin down.
That's because, genetically speaking, dogs are a mess. They've been moved around the world for centuries, mixing their genomes indiscriminately at far-flung ports of call, and even — early in their evolution — mating with their wild counterpart, the wolf. Adding to the confusion is the intensive period of selective dog breeding that started in the late 1880s and gave humans the wide variety of dog breeds known today. [What Your Dog's Breed Says About You]
Archaeologists have found definite evidence of domestication in the form of dogs and humans buried together at least 14,000 years ago. Some have suggested domestication occurred earlier than that, perhaps as long as 33,000 years ago, based on some doglike skulls found in Belgium and in Siberia.
Original genetic analyses put dog domestication much earlier, with researchers writing in a 1997 paper in the journal Science suggesting that dogs diverged from wolves more than 100,000 years ago.
Those studies compared modern dogs with modern wolves, however, the analysis was muddied by dogs' weird breeding history. In the new study, published Friday (Nov. 15) in the journal Science, scientists analyzed ancient DNA from prehistoric dog fossils found in Europe and the New World.
The researchers sequenced mitochondrial DNA from these fossils. Mitochondria are tiny organs inside cells that generate the energy that cells need to run. The genes that control the mitochondria are passed down the maternal line.
Comparing the ancient mitochondrial DNA with the mitochondrial DNA of modern dog breeds and wolves revealed a common link to Europe, the researchers found.
"Dogs seem to have been domesticated or first evolved from a population of ancient wolves living in Europe," said study researcher Robert Wayne, a professor of ecology and evolutionary biology at the University of California, Los Angeles. "That ancient wolf population is now extinct."
"We've kind of made mistakes [in previous studies] assuming that ancient wolves and modern wolves are direct ancestors and descendants," Wayne told LiveScience.
The finding suggests that wolves first started hanging around humans during a time when people hunted large animals like mammoth. The remains of mammoth and other megafauna carcasses would have been good eating, and friendlier wolves may have gradually started interacting with the human hunter-gatherers. [The 10 Most Popular Dog Breeds]
The study researchers also examined some of the most controversial prehistoric canid fossils, including one found in a cave in the Altai Mountains of Siberia and others discovered in Belgium. These remains date as far back as 36,000 years ago. The new study finds that the Siberian and Belgian pooches were not direct ancestors to modern dogs. It seems they may have been an unknown species of doglike wolf, or they may have been an "aborted domestication event," Wayne said.
A European story
Genetics is a tricky way to try to establish the timing of dogs' emergence, said Clive Wynne, a dog cognition researcher at Arizona State University who was not involved in the study. Many of the genetic techniques used were developed to trace the divergence of species over millions of years. Dog domestication happened much more quickly, and a few thousand years makes a big difference in whether dogs were originally the pets of hunter-gatherers or more sedentary farmers, Wynne told LiveScience.
Most researchers already agreed that the rise of dogs occurred before the rise of agriculture, said Greger Larson, an archaeologist and geneticist at Durham University in the U.K. who was not involved in the study. But the new geographical information linking dogs to prehistoric Europe is "a really big step in the right direction," Larson told LiveScience.
"What it absolutely establishes is that there are canids in Europe that are contributing DNA to modern dogs and that Europe is, without question, part of the story," Larson said. "Zooarchaeologists and archaeologists have known that for a long time, but the genetic data has not backed that up."
The next step is to delve into the nuclear DNA of ancient dogs, Wayne and Thalmann said. The DNA in a cell's nucleus is passed down from both parents, and thus holds information the maternal mitochondrial DNA doesn't. It was nuclear DNA studies that revealed Neanderthals and modern humans interbred, for example. New genetic techniques should make similar studies possible in dogs, Larson said.
"That'll be a game-changer," he said.
Genetic research is also revealing the changes necessary to turn a dog into a wolf. A study published in January in the journal Nature found that, unlike wolves, dogs have evolved the ability to eat starchy food — a talent that may have given them a paw up in surviving off human trash.