For decades, geneticists, archaeologists, and evolutionary biologists have been trying to trace the history of Canis lupus familiaris (dogs), with conflicting results. Genetic studies have proven challenging because the explosion in canine breeds over the last couple of centuries has obscured the dogs’ evolutionary history. “You don’t get a picture of what went on 20,000 years ago,” about the time dogs may have been domesticated, says Adam Boyko, a geneticist at Cornell University.
So Boyko decided to look at dogs that live in isolated places and that are typically left alone to mate as they see fit. He and his brother traveled around the world sampling DNA
from about 549 “village” dogs—animals that often don’t really belong to anyone but hang around people anyway—from 38 countries. Boyko and his Cornell postdoc Laura Shannon then compared these dogs’ genomes, as well as the genomes of more than 4500 purebreds from 161 breeds, at almost 189,000 spots along their chromosomes.
“It’s a really comprehensive work including all kinds of markers, and a fairly good geographical coverage,” says Peter Savolainen, an evolutionary geneticist at the Royal Institute of Technology, Stockholm, who has also sampled dogs from around the world to determine their evolutionary birthplace. “So, it gives a good picture of the overall genetic relations among today’s dogs.”
Village dogs had a much wider variety of genetic differences than purebred dogs and thus are better sources of historical data, Shannon, Boyko, and their colleagues report online today in the Proceedings of the National Academy of Sciences. These dogs had experienced different degrees of infiltration from European canines: African dogs have relatively few European dogs in their past, whereas dogs in the South Pacific came almost exclusively from European stock, they discovered. Such a strong European influence also obscures the historical signal, so Boyko’s team focused on data from indigenous dogs with little modern European influence.
In this subset, the team homed in on the number of differences at spots located close to one another along their genomes. This indicated how far back in time these dogs descended from a common ancestor—and where this happened. The analysis pointed toward central Asia as the place where dogs likely transitioned from wolves. It also indicated that dogs then moved into east Asia and elsewhere. They were not able to pin down a date for this transition.
Boyko suspects that between 50,000 and 10,000 years ago, grey wolves and humans were hunting large mammals like elk in central Asia. But increasing human density, climate change, or other factors may have resulted in scarcities in these prey, such that wolves began scavenging to survive. Hanging around human encampments led to smaller, tamer animals that may have begun to cooperate with people, kicking off domestication.
Not everyone agrees with the team’s findings. Boyko’s sample didn’t include animals from south or central China, and if they had “it might possibly have indicated these regions instead,” says Savolainen, whose work suggests just that. Robert Wayne, an evolutionary biologist and dog domestication expert at the University of California, Los Angeles, is also skeptical: One lesson learned from genetic studies of dog domestication is that looking at dogs living today “are a poor guide to domestication events which may have occurred more than 27,000 years ago.” To get around that problem, Wayne, Savolainen, and Larson are now looking at fossil DNA as well as modern DNA. However, the new study will be of great help for this work, Larson says. “Once we have the ancient data, we can compare it against [Boyko’s] to really get to grips with where and when dogs were domesticated.”