Evolutionary biologists have long debated where the first wolf-to-dogs transition occurred and whether a second such transition occurred in the New World. They are hampered by a sparse and confusing fossil record. So Jennifer Leonard, now an evolutionary biologist at the Smithsonian National Museum of Natural History in Washington, D.C., and her colleagues turned to DNA preserved in fossil bones.

Working with Robert Wayne of the University of California, Los Angeles, Leonard studied DNA from 37 dog bones found at pre-Columbian archaeological sites in Mexico, Peru, and Bolivia, as well as 11 DNA samples from dog remains deposited in Alaska before the arrival of the first European settlers. The ancient DNA was just like modern Eurasian dog DNA, the team reports in the 22 November issue of Science, indicating that these ancient dogs were close kin to their Old World counterparts. The American gray wolf proved to be just a distant cousin. It appears that “dogs accompanied humans into the New World” and sired New World canines, says David Hillis, an evolutionary biologist at the University of Texas, Austin.

These Old World dogs first appeared in East Asia, most likely China, according to work by Peter Savolainen of the Royal Institute of Technology in Sweden and his colleagues. Savolainen's DNA studies involved some 500 samples from modern dogs and about 40 from wolves. As they report in the same issue of Science, the DNA sequences were similar enough to suggest that the ancestors of all these animals came from the same place. He and his colleagues determined that dogs from East Asia had the most ancient pedigrees and were likely the source of the rest of the world's canines.

"It was very excited to read these articles," says John Olsen, an archaeologist at the University of Arizona, Tucson. "The evidence is bringing us closer to a resolution [of these questions]."

--ELIZABETH PENNISI