When and where did humans make prehistoric wolves a favorite pet? An international group of biologists and archaeologists comes up with a new hypothesis:dogs were domesticated twice before the advent of agriculture, once in Asia and separately also in Europe. The study appeared this week in Science .
Due to domestication, wolves turned into dogs twice, once in Asia and once in Europe. That is the new hypothesis of a large group of scientists about the origin of our four-legged friend. Evidence from ancient and modern canine DNA and archaeological remains tell a new story of the dog's pet history. The study is featured this week in Science.
Contradictory reconstructions
The evolutionary history of the domestic dog—where and when the beast was domesticated—is a controversial mishmash. Archeology and genetics tell different stories. For example, it has been suggested that the animal first appeared on the scene 30,000 years ago. Remains, on the other hand, clearly indicate that the dog emerged in the late Stone Age, 15,000 years ago in Europe and 12,500 years back in East Asia. Genetic studies, in turn, showed that dogs were domesticated once, but there is debate as to where that happened next.
Split
The researchers from the United Kingdom, Ireland, France and Germany, among others, looked at pieces of DNA from dozens of ancient dogs (14,000-3,000 years old) and the complete genome of a 4,800-year-old dog. They compared those ancient DNA samples with DNA samples from two and a half thousand modern dogs.
Tens of thousands of specific positions in the DNA of each sample were checked to see which letter was there. In this way, each sample is given a unique genetic signature. Based on the differences between these 'signatures', the researchers made an evolutionary family tree, which shows to what extent the different DNA samples are related to each other.
The tree clearly showed a genetic division between modern East Asian and modern European dogs. What is striking is the timing of the split:it happened after the first dogs appeared in Europe, which according to the archaeological evidence was 15,000 years ago. This indicates that dogs have been domesticated independently in both Europe and East Asia from different wolf populations.
"The fact that until now there has been no consensus about where dogs are domesticated may be because everyone was somewhat right," said study leader Greger Larson of Oxford University in a press release.
DNA in the mix
A scenario in which dogs originated in one place and spread soon after, the team considers unlikely. No remains of dogs older than 8,000 years have ever been found in Eurasia, the region between East Asia and Europe. This observation also points to the fact that two different groups of dogs lived on the Eurasian continent in the Stone Age.
The authors think that the eastern dogs spread westward, along with humans. Once there, they partially replaced the original population of European dogs. The DNA of modern European dogs is very different from the DNA of prehistoric European dogs. It probably changed a lot when the eastern neighbors arrived.
Revised history
Hannes Schroeder, assistant professor at the Natural History Museum of Copenhagen and senior researcher at Leiden University, thinks the evidence for this hypothesis is strong. He was not involved in the research, but specializes in ancient DNA.
“The strength of this study is that the researchers base themselves on multiple data sets. They bring all the evidence together and unite the different theories into one story,” said Schroeder. “Maybe the theory will change a bit as new remains emerge, but it will be a refinement and not a drastic change.”
Is it possible that dogs have been domesticated more than twice, three or even four times? Schroeder does not see why not, although there is currently no indication of this. “But it will be very difficult to ever prove that.”