Sled dogs have well-known roots in human prehistory. A 12,500-year-old tool found at one Arctic site hints at its possible use on sleds. And archaeological investigations at a well-known site on Zhokov Island in the Siberian Sea uncovered dog bones and sled technology indicating that the dogs may have been the first canines bred for a specific task.
Dr. Sinding and colleagues dug deep into the DNA of one of those dogs, using a jawbone from the site dating to 9,500 years ago. They also sequenced the genomes of a Siberian wolf dating to 33,000 years ago and 10 modern Greenland sled dogs. They relied on other canine genomes archived in databases as well.
They found that the Zhokov dog was closest to modern-day sled dogs, particularly to the Greenland sled dogs, which are a “land race,” bred for a task and sharing a look and behavior but not the sort of breed for which studbooks and records are kept.
The Zhokov dog was not a direct ancestor of modern sled dogs, but it shared a common ancestor with modern sled dogs that was probably about 12,000 years old. This evidence suggested that the sled-dog type, bred for hauling loads in brutal winters, was already established 9,500 years ago.
The researchers also found that sled dogs, ancient and modern, did not show interbreeding with wolves, even though other modern dog breeds do, and dog-wolf matings were known in Greenland in historic times. The results suggest hybrids may not have been much use in pulling sleds.
Then the researchers started looking for genes that were different in sled dogs from both wolves and other dog breeds. They found several that made sense. One is involved in a variety of physiological functions including calcium transport and temperature sensitivity. They don’t know what exactly it does in sled dogs, but they do know that several similar genes are different in mammoths, creatures of the cold, and elephants, animals of more temperate climates, suggesting some kind of adaptation to arctic life.
Another gene that distinguished sled dogs from other dogs is involved in coping with low oxygen conditions. It is also found in a group of humans, sea nomads, who have been diving for thousands of years. It could, Dr. Sinding said, contribute to fitness for the extreme demands of long sled-hauling trips.