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There are about 90 million dogs living in North America, but where did they all come from?
A groundbreaking study has traced the genetic history of dogs on the continent, and found evidence that the animals have been living there for at least 10,000 years, and potentially earlier - ever since the first humans arrived.
An international team of scientists, including geneticists from the Museum, have sequenced the genomes of 71 dogs from North America and Siberia.
They found that the ancient American dog population was largely replaced when European colonists arrived on the continent.
Modern dogs are all descended from grey wolves. But modern American dogs were not domesticated from native wolves as has been thought, but instead were imported to the continent from Europe and Asia.
Scientists hope combined archaeological and genetic approaches, such as this study, will contribute to a clearer understanding of the history of human migration into the Americas and human movement within the continents.
Dr. Angela Perri of Durham University was the lead archaeologist on the project.
She says, 'The combined approach of using archaeology and genetics together allows us a much clearer window into the past.’
'By analysing the ancient DNA of dog remains from archaeological sites we can get a better understanding of where these dogs come from, when they arrived into the Americas, and their relationship to other dog populations in different parts of the world.
'This knowledge may help us to better understand the movement of people into the Americas, using dogs as a proxy for human migration.'
Helped by the Museum's ancient DNA lab, the team sequenced 71 mitochondrial genomes (those passed from a mother to a puppy) and seven nuclear genomes. They compared that data to the genes of modern dogs.
Their findings suggest that the most ancient dogs in America have left almost no genetic trace in modern populations, having been virtually wiped out over thousands of years.
There have been four waves of dogs into the Americas, and researchers have demonstrated that their arrivals coincided with the early migration of humans there.
The first wave was between 17,500 and 13,000 years ago, when the first Palaeolithic human hunter-gatherers arrived from Siberia. Early humans probably relied on their canine companions for survival, using them for sledging, a source of food and warmth, protection, alarms and keeping predators away.
The second wave was about 1,000 years ago, when Artic dogs were brought by the Thule people to Alaska, northern Canada and into Greenland. These animals are the ancestors of modern Alaskan malamutes, Alaskan huskies and Greenland sledge dogs.
European settlers brought the third introduction of dogs with them from 1492, and the last wave was in the nineteenth century, when Siberian huskies were introduced to the American Arctic during the Alaskan gold rush.
Nothing remains of that first wave of ancient American dogs. The population was almost completely replaced by subsequent arrivals – perhaps through a human preference for specific breeds, or perhaps because a disease killed off earlier populations.
Now all modern dogs in America have a Eurasian origin and are related to those that arrived with European settlers, although a few older Arctic dogs do still remain. The oldest lineages are huskies and Greenland dogs.
Although the ancient dogs of America are now lost, their genes do survive in one peculiar form.
The closest surviving genetic trace is in a contagious form of cancer called Canine transmissible venereal tumour, or CTVT. It spreads between dogs by the transfer of living cancer cells during mating.
It first originated from the cells of an individual dog that lived up to 8,000 years ago, and the cancer still carries the genome of that dog. It can now be found in dogs all over the world.