Dogs have ancient origins, dating back perhaps 100,000 yearsor more -- much older than scientists had thought, UCLA scientists andcolleagues found.
While many scientists believed, based on archaeologicalrecords, that domestic dogs dated back only 14,000 years, molecular genetictechniques reported in the June 13 issue of the journal Science show that man'sbest friend is much older. The newresearch also confirms that dogs evolved from wolves.
"Our data show that the origin of dogs seems to be much moreancient than indicated in the archaeological record," said Robert K. Wayne,UCLA associate professor of biology."The origin of dogs dates well before the development of agriculturalpopulation centers that occurred approximately 10,000-14,000 years ago, andgoes back to hunter-gatherer societies.While many people think a high level of sophistication was required todomesticate wild mammals, our data imply that very primitive societies may havehad domestic animals."
Scientists believe from archaeological records that manydomestic animals, including cats and cattle, originated within the last 14,000years. Cats may have been domesticatedas recently as 7,000 years ago, Wayne said.
Wayne noted that his techniques do not enable exact dates tobe determined for dogs. "Because of theextrapolation involved in the calculations, it's possible that the first dog
dates back 60,000 years, or perhaps more than 100,000years," he said.
For the research, Wayne and his colleagues studied DNAsequences from 140 dogs representing 67 breeds -- including golden retrievers,German shepherds, collies, St. Bernards, poodles, bulldogs, Irish setters,rottweilers, English sheepdogs, fox terriers and chow chows. They also analyzed 162 wolves from the UnitedStates, Canada, Mexico, Russia, China, India, Italy, Portugal, Spain, France,Sweden, Saudi Arabia, Israel and other countries, as well as jackals andcoyotes.
The scientists analyzed DNA sequences from the controlregion of the mitochondrial genome -- a region with a high mutation rate. They were surprised by the great diversity ofDNA sequences they found within dogs.
"We expected to find DNA sequences in dogs that were closelyrelated to those in wolves, perhaps even indistinguishable from those inwolves," Wayne said. "We expected tofind a few different sequences in dogs; instead we found 26.
"We initially suspected the amount of genetic diversity inthe marker we analyzed would be very low because the only way that diversityaccumulates is through DNA mutations over time, and 14,000 years is not enoughtime for many mutations to appear.
"We have found that the origin of dogs is much older thanpreviously believed because the genetic diversity within dogs is much greaterthan one would find if their origin were as recent as 14,000 years ago," Wayneadded. "Given the amount of geneticdiversity that we found, we can calculate how long it should have taken toachieve this diversity if mutations alone were driving the process. Our calculations suggest the first domesticdog might be as old as 100,000 years or older."
While some scientists thought that dogs evolved from jackalsor coyotes, Wayne and his colleagues found no evidence to support this theory.
"Dogs clearly evolved from wolves," Wayne said. "We found dog sequences whose closestrelatives are wolves, which implies infrequent inter-breeding between dogs andwolves. We studied sequences of jackalsand coyotes, and found no resemblance to any sequences in dogs."
Most modern breeds of dogs are very recent in origin --within the last few hundred years, due to modern breeding practices, Waynenoted. In the Middle Ages, there wereonly a few types of dogs, he said.
The scientists on the study also include Carles Vila, apostdoctoral scholar in Wayne's lab; Jesus Maldonado and Isabel Amorim, UCLAgraduate students in Wayne's lab; Rodney Honeycutt, a faculty member at TexasA&M University; John E. Rice, a graduate student in Honeycutt's lab; JoakimLundeberg at the Royal Institute of Technology in Stockholm, Sweden; PeterSavolainen, a research assistant in Lundeberg's lab; and Keith A. Crandall,assistant professor of zoology at Brigham Young University.
The research was funded by the National Science Foundation.