From tiny chihuahuas to fluffy Siberian huskies, dogs come in all shapes and sizes. But researchers have revealed there is more to canine diversity than meets the eye.
Scientists have found five distinct groups of dogs were already present at the end of the last ice age, and their legacy lives on in our pets today.
“[If] I walk through Wimbledon Common I am pretty likely to run across dogs that all have a little bit [of a] different history, tracing back as far as 11,000 years ago to different corners of the world,” said Dr. Pontus Skoglund, co-author of the study and group leader of the ancient genomics laboratory at the Francis Crick Institute in London.
Writing in the journal Science, Skoglund and colleagues report how they sequenced 27 ancient dog nuclear genomes from canines found in Europe, the near east, and Siberia, dating from 800 to 11,000 years old.
The results reveal that by the end of the last ice age there were at least five genetically distinct groups of dogs in existence – suggesting the origins of our canine companions stretch back even further. However, all the groups appear to have descended from a single common ancestor, suggesting domestication may have occurred from a single population of ancient wolves.
The researchers made further revelations when they compared their results with DNA from modern dogs, finding that breeds that originated in Europe, such as the German shepherd or Irish terrier, all appear to be descended from a roughly 50/50 mix of two of the ancient groups – those from the Levant and northern Europe.
“Those ancestries came together in Europe, probably when the first farmers came into Europe and they brought their dogs and they met the dogs that were already there,” Skoglund told the Guardian.
“Breeds in Europe today are less genetically distinct than the two in prehistory, in that they have a less deep history that doesn’t stretch back thousands of years,” he added, although he noted artificial selection had led to breeds with particular traits.
The team found that while DNA from modern European dogs has contributed to breeds around the world, traces of the other ice age groups remain – including in chihuahuas, a breed with roots in Mexico.
“During the colonial era [modern European breeds] spread around the world, which is why you see a chihuahua is mostly [of that ancestry],” said Skoglund. But, he added, 4% of chihuahua DNA came from an ice age group from ancient America.
Similarly, the Siberian husky, while carrying DNA from modern European dogs, also contains DNA from an ice age group from Russia, while the Rhodesian ridgeback has some ancestry from another ice age group.
The team also used human and canine genetic data to explore whether dogs kept heeling as people moved across the world.
The results reveal that in many cases, people and their dogs appear to have moved together, but that was not always the case. For example, while both dogs and people moved from the Levant to Europe during the agricultural expansion, only humans retained distinct ancestries in the aftermath.
“The fact that we see sometimes the history doesn’t match, could mean people would move around while leaving their dogs behind, or having preferences for other types of dogs, but it could also be due to dog dynamics,” said Skoglund, noting another possibility was that dogs could have been traded.
Despite the new insights, questions remain, including when and where the first dogs were domesticated. “That’s a huge mystery,” said Skoglund.
Dr. Elaine Ostrander, an expert in canine genetics from the National Human Genome Research Institute in the US, who was not involved in the study, said the work was exciting.
“Perhaps the most compelling conclusions relate to their comparison of human-dog genomes,” she said, adding: “The identification of events where dogs moved between different human groups, or humans dispersed without dogs provides a granularity that we have not previously had in addressing these issues.”