|(Photo courtesy of the Center for American Archeology/Del Baston) Koster, Illinois, ancient dog skeleton|
The fate of the indigenous dogs of the New World in the aftermath of European colonization has long piqued the interest of both academics and dog lovers. Some modern breeds, such as Catahoulas and Mexican and Peruvian hairless, are widely thought to have ancestors who lived before Columbus' arrival. Geneticists have recently investigated how much ancient DNA these and other breeds actually carry. Now, a large-scale study conducted by an international multidisciplinary team suggests that they have little, if any, indigenous American ancestry.
According to this study, modern American dogs are nearly entirely descended from European dogs that arrived 500 years ago. "The indigenous American dogs appear to have been almost completely wiped out," says Angela Perri, a zooarchaeologist at Durham University in England who took part in the research. This new discovery contradicts other genetic studies that suggest some dogs still carry indigenous DNA.
Perri and her colleagues examined complete genomes recovered from the remains of seven ancient dogs from Siberia and North America, as well as those of over 5,000 modern dogs. They also looked at 71 mitochondrial DNA samples from ancient dogs. Mitochondria are organelles that generate energy within living cells. They have their own genomes, which they inherited from their mothers. According to the team's findings, dogs were brought to the Americas in four migrations.
The first dogs would have arrived from Asia 9,900 years ago, thousands of years after the first humans. The second group of dogs may have been introduced to the Arctic by the Thule people, the Inuit's ancestors, around 1,000 years ago. The third migration began 500 years ago with the establishment of European colonies, and the last occurred around 1900 when huskies were brought to Alaska from Siberia during the Gold Rush. The team believes that the last two migrations resulted in the near-complete extinction of the Americas' indigenous dogs.
According to Perri, there could be several reasons for this. "Things like canine distemper or rabies may have arrived with European dogs and impacted native dog populations," she says. Perri also cites historical documents that describe Spanish explorers eating native dogs and notes that English colonists freely slaughtered native dogs and prevented them from breeding with European dogs.
Peter Savolainen, an evolutionary geneticist at the Royal Institute of Technology in Stockholm, led another recent study of American dog DNA. His team examined mitochondrial DNA in 2,000 modern dogs and discovered evidence of widespread replacement of indigenous dogs, as well as traces of ancient DNA in the modern samples.
According to Savolainen, "there is still a small percentage of ancient American ancestry in modern American dogs." His team's analysis revealed that Chihuahuas are related to Mexico's indigenous dogs and that the Carolina Dog, a free-roaming breed from the southeastern United States, has approximately 30% American ancestry. They discovered no European ancestry in Inuit dogs.
Several factors could account for the disparity between the teams' findings. Savolainen admits that his study would only have detected ancestry in female dogs because he did not examine entire genomes like Perri's team did. This may have skewed the results. Furthermore, Perri speculates that Savolainen's team may not have distinguished between modern Arctic dog ancestry and precontact dog ancestry because both carry similar types of mitochondrial DNA. Nonetheless, Perri admits that her team's study was unable to collect DNA from every dog population in the Americas. "It's likely that there are isolated populations of dogs in South and Central America that are descendants of the precontact group of dogs," she says.