When, where and how often were dogs domesticated? Despite many years of research, these questions have not yet been fully clarified. Now researchers have added another piece of the puzzle. They analyzed 72 ancient wolf genomes spanning 100,000 years. The result: the ancestors of today’s dogs go back to at least two different wolf populations. The four-legged friends were therefore either domesticated at least twice independently of one another, or already domesticated dog ancestors mixed with wild wolves.
Dogs have been man’s best friend for at least 15,000 years. However, when and where exactly their ancestors, the wolves, were domesticated is still unclear. Many researchers have worked on the basis of archaeological finds and DNA analyzes to narrow down the time and place of domestication more precisely. Some studies place the cradle of the modern dog in Europe, others in Central Asia. However, comparisons of modern genomes only allow limited conclusions to be drawn.
Dual Lineage of Dogs
In order to get closer to the answer to the question of the origin of dogs, a team led by Anders Bergström from the Francis Crick Institute in London has now analyzed 72 ancient wolf genomes from Europe, Siberia and North America, dating back 100,000 years. “Through this project, we have greatly increased the number of ancient wolf genomes that have been sequenced, which allows us to build a detailed picture of the ancestry of wolves over time, including the time when dogs arose,” says Bergström.
The scientists found that traces of the genome of Ice Age wolves from Asia can be found in all modern-day dogs. For early dogs from Northeast Europe, Siberia, East Asia and America, this eastern wolf population appears to be the sole ancestor. “However, for dogs in the Middle East and Africa, we found that up to half of their ancestry traces back to a population related to modern southwestern Eurasian wolves,” the researchers report.
Domestication Scenarios
There are two possible explanations for this finding: On the one hand, it could be that wolves in both eastern and western Eurasia were independently domesticated and began to accompany humans. These initially separate populations of early dogs may later have intermingled. On the other hand, it is conceivable that domestication took place only once in Asia and that the dogs later, after migrating to Europe together with human settlers, mixed with wild wolves native there. Which of these two scenarios took place cannot be determined on the basis of the current state of research.
“None of the ancient wolf genomes we examined directly match any of these canine ancestors, meaning the exact ancestor populations have not yet been found,” the researchers write. While it was previously assumed that the direct ancestors of dogs are now extinct, Bergström and his team consider it plausible on the basis of the genome analyzes that wolves alive today could have emerged from the ancestor population of dogs, albeit through ongoing genetic changes far removed from the dogs that they can no longer be recognized as direct relatives.
Watch evolution in real time
Because the 72 ancient wolf genomes span around 30,000 generations, it was possible to create a timeline of changes in wolf DNA and thus track natural selection. In several cases, the researchers observed mutations spreading throughout the Eurasian wolf population. “This was possible because the species were closely associated across large distances. This connectivity may be one reason why wolves survived the Ice Age while many other large carnivores disappeared,” says Bergström’s colleague Pontus Skoglund.
For example, one of these mutations affected a gene involved in the development of the bones of the skull and jaw. Within 10,000 years, this initially very rare variant spread to all wolves in the population – possibly because changes in prey during the Ice Age gave wolves with a specific jaw shape advantages. “This is the first time that scientists have directly tracked natural selection in a large animal over a 100,000-year period, allowing them to observe evolution in real time rather than trying to reconstruct it using modern-day DNA,” Skoglund said.
Source: Anders Bergström (Francis Crick Institute, London) et al., Nature, doi: 10.1038/s41586-022-04824-9