Domesticated dogs first appeared in East Asia, spread across Asia and Europe, and then accompanied their two-legged companions into the Americas some 12,000 to 14,000 years ago, according to research published in the US-based Science magazine last Friday.
That is the scenario pieced together by researchers from China and Sweden, who traced the genetic origins of dogs living on both sides of the Pacific.
Humans may have domesticated dogs from wolves as recently as 15,000 years ago, according to the study by Peter Savolainen of the Royal Institute of Technology in Stockholm, who performed the research in collaboration with his Chinese partners.
Under a joint research program, the Chinese and Swedish scientists analyzed DNA samples taken from 654 dogs in Asia, Europe, Africa, and North America over the past two years.
They found that, while most dogs share a common gene pool, genetic diversity is the highest in East Asia, suggesting dogs have been domesticated there the longest.
Previously, researchers generally looked to the Middle East as the setting for the first domestication of plants and animals.
Zhang Yaping, a researcher with the program at the Kunming Institute of Zoology under the Chinese Academy of Sciences, said the hypothesis that dogs were first domesticated in East Asia has long been advanced based on anatomical studies but had not been confirmed by genetics until the publishing of this research.
The body structures of dogs may change greatly due to cross-breeding, but the genetic information stored in their DNA, that links them with their ancestors, remains stable over a significantly long period of time, Zhang said.
Over the past decade, genetic studies of the origins of life on earth have provided more insight into animals and plants and have sometimes even overturned previous research results.
But the study of the dogs' genetic origins had not gained momentum until Savolainen hit upon the idea when he was doing other research two years ago.
Savolainen started studying dog genetics to help police analyze hairs. "I've been to a lot of dog shows here, snatching hairs from the dogs," he was quoted as saying by the magazine.
As he assembled a large collection of dog hairs and attached cells, he began to wonder whether he could expand his study and find the cradle of the domestic dog.
He and Zhang's team focused on stretches of DNA from the cells' mitochondria, which function like power houses and pass from mother to pup.
Based on similarities in that genetic material, 95 percent of the dogs that the researchers sampled had come from just three lineages that seem to have arisen in East Asia.
"This finding corresponds well with the previous hypothesis based on observations of anatomy," Savolainen said.
A second international research team investigated whether dogs in America were domesticated from wolves there, independently from Old World dogs, or whether the two groups were related.
Jennifer Leonard and her colleagues at the University of California in Los Angeles compared the DNA sequences of New and Old World dogs, including some Latin-American and Alaskan dogs that pre-dated the first European explorers in the Americas.
The DNA sequences were derived from remains up to 1,400 years old. Thirty-seven came from archaeological sites in Peru, Bolivia and Mexico, and 11 from modern gold mines in the Alaskan permafrost.
The similarities among the DNA sequences of New and Old World dogs indicate that all the dogs share a common ancestor.
A certain cluster of sequences from the ancient Latin-American dogs did not match any from modern dogs, indicating that European colonists probably did not use Native-American dogs to create the breeds that we know today, according to the researchers.
The researchers constructed a family tree including modern dogs and wolves that suggests the ancient New World dogs were much closer to Old World dogs than to New World wolves.
The two new studies agree with suggestions from older work: Dogs were domesticated in the Old World, and the earliest migrants brought them to the New World through land bridge across the Berling Strait, Zhang said.
He also said they are now in the process of identifying the origins of domesticated pigs, chickens, yak and cattle using the same approach.
(China Daily November 27, 2002)
