Though dogs are humanity's oldest and most consistent animal friend, scientists have long struggled to figure out just how Canis familiaris came to be. Though researchers agree dogs are descended from wild wolves, they aren’t sure when and where domestication occurred. And as Tina Hesman Saey at Science News reports, a new study has revived the debate, suggesting that dogs were domesticated one time between 20,000 and 40,000 years ago.
Dog domestication has gotten a lot of attention in recent years. In 2016, researchers looked at the mitochondrial DNA of modern and ancient dog species, determining that dogs come from two different wolf populations, one found in Europe and one found in Asia. That means that wolves would have been domesticated in two different places, with the two lineages eventually mixing in modern dogs.
But this latest research contradicts the double-domestication hypothesis. According to Ben Guarino at the Washington Post, researchers looked at the well-preserved DNA of two ancient dogs found in Germany, one 7,000 years old and one 4,700 years old, as well as the complete genomes of 100 modern dogs and snippets of DNA from 5,600 other wolves and dogs.
They traced the rate of mutations in the over time in the dog genomes. This technique, which creates a “molecular clock,” indicates that dogs diverged from wolves 36,900 years ago to 41,500 years ago in a single domestication event. But they can't determine exactly where the split occurred. About 20,000 years later, the molecular clock indicates dogs split into European and Asian groups. They published their results in the journal Nature Communications.
Not everyone is convinced by the study. Greger Larson, Oxford evolutionary biologist and author of the earlier domestication study, tells Guarino that the latest research does not explain the “ridiculously deep split” between the genetics of ancient European and Asian dogs. He also points out that while ancient dog bones have been found in far eastern Asia and western Europe, the middle of Eurasia seems to be empty of dog bones, suggesting that there were two ancient populations, separated by vast distances.
Krishna Veeramah, a palaeogeneticist at Stony Brook University and author of the new study says he doesn’t anticipate that the paper will put the issue to rest. “More ancient dog DNA from genomes will ultimately solve the problem,” he tells Rachael Lallensack at Nature. Researchers are hoping to find more geographically diverse DNA from dogs as well as samples from different time periods.
Whether it happened once or twice, how and why did domestication occur?
As Veeramah tells Helen Briggs at the BBC that it’s likely dogs evolved from wolves that began hanging around human camps, scavenging their scraps. ''Those wolves that were tamer and less aggressive would have been more successful at this," he says. “While the humans did not initially gain any kind of benefit from this process, over time they would have developed some kind of symbiotic relationship with these animals, eventually evolving into the dogs we see today.”
One early benefit of domesticated dogs may have been that they could help transport meat from carcasses or hunt dangerous game like cave bears and cave lions, Saey writes in an earlier Science News article.
For now, however, exactly when and where Fido first approached humans will remain a mastiff question.