Dogs (Canis lupus familiaris) arrived in the Americas only about 10,000 years ago, thousands of years after the first human migrants crossed the Bering land bridge, according to a new study published in the Journal of Human Evolution.
Scientists analyzed DNA from ancient dog remains from more than a dozen sites in North and South America. This illustration shows a Canadian Eskimo Dog by John James Audubon and John Bachman (1845-1848).
The study looked at the genetic characteristics of 84 individual dogs from more than a dozen sites in North and South America, and is the largest analysis so far of ancient dogs in the Americas.
Unlike their wild wolf predecessors, ancient dogs learned to tolerate human company and generally benefited from the association: they gained access to new food sources, enjoyed the safety of human encampments and, eventually, traveled the world with their two-legged masters.
Dogs also were pressed into service as beasts of burden, and sometimes were served as food, particularly on special occasions.
“Their 11,000 to 16,000-year association with humans makes dogs a promising subject for the study of ancient human behavior, including migratory behavior,” said Kelsey Witt of the University of Illinois, who is the lead author on the study.
“Human remains are not always available for study because living populations who are very connected to their ancestors in some cases may be opposed to the destructive nature of genetic analysis.
“Analysis of ancient dog remains is often permitted when analysis of human remains is not.”
Previous studies of ancient dogs in the Americas focused on the dogs’ mitochondrial DNA, which is easier to obtain from ancient remains than nuclear DNA and, unlike nuclear DNA, is inherited only from the mother. This means mitochondrial DNA offers researchers an unbroken line of inheritance back to the past.
The new study also focused on mitochondrial DNA, but included 42 pre-Columbian dogs from three sites located in Illinois, coastal British Columbia, and Colorado – a much larger sample than had been analyzed before.
A site in southern Illinois known as Janey B. Goode is located near the ancient city Cahokia, the largest and first known metropolitan area in North America. Its occupation occurred between 1,400 and 1,000 years ago, while Cahokia was active from about 1,000 to 700 years ago.
Dozens of dogs were ceremonially buried at Janey B. Goode, suggesting that people there had a special reverence for dogs. While most of the dogs were buried individually, some were placed back-to-back in pairs.
In Cahokia, dog remains, sometimes burned, are occasionally found with food debris, suggesting that dogs were present and sometimes were consumed. Dog burials during this time period are uncommon.
As previous studies had done, Kelsey Witt and her collaborators analyzed genetic signals of diversity and relatedness in a special region of the mitochondrial genome of ancient dogs from the Americas.
They found four never-before-seen genetic signatures in the new samples, suggesting greater ancient dog diversity in the Americas than previously thought.
They also found unusually low genetic diversity in some dog populations, suggesting that humans in those regions may have engaged in dog breeding.
In some samples, the group found significant genetic similarities with American wolves, indicating that some of the dogs interbred with or were domesticated anew from American wolves.
But the most surprising finding had to do with the dogs’ arrival in the Americas.
“Dog genetic diversity in the Americas may date back to only about 10,000 years ago,” Kelsey Witt said.
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Kelsey E. Witt et al. DNA analysis of ancient dogs of the Americas: Identifying possible founding haplotypes and reconstructing population histories. Journal of Human Evolution, published online December 18, 2014; doi: 10.1016/j.jhevol.2014.10.012
