In an intriguing reassessment of man's best friend, researchers at UCLA have determined that the partnership between human beings and dogs began more than 100,000 years ago--long before the advent of the household cat or any other domesticated animal, before the dawn of civilization itself.
Indeed, based on this most recent finding, it could be said that humanity's first civilized act on the road to modernity was to get a dog.
A sophisticated genetic analysis of 67 dog breeds from around the world made public Thursday also shows that all of today's many kinds of canines--the schnauzers, pugs, shepherds, hyperactive poodles, housebroken otter hounds and lap dogs of millions of homes--are essentially domesticated wolves.
They all evolved directly from only one ancient canine forebear--the wolf--with no ancestors among coyotes, jackals, dingoes or other similar species. The research is being published today in Science.
"The origin of dogs is very old--perhaps 100,000 years ago or more," said Robert K. Wayne, a UCLA evolutionary biologist who led the international study. "That contradicts the archeological date," which suggests that dogs first appeared 14,000 years ago.
"While many people think that a high level of sophistication was required to domesticate wild mammals, our data imply that very primitive societies may have had domestic animals," he said.
Wayne collaborated on the research with UCLA biologists Carles Vila, Jesus E. Maldonado and Isabel R. Amorim, Keith Crandall at Brigham Young University and researchers from the Royal Institute of Technology in Stockholm.
At least one expert on the evolution of dogs, however, did not find the date credible. "I don't believe the evidence for that early date is conclusive," said Stanley J. Olsen, a senior vertebrate paleontologist at the University of Arizona. He says there is no fossil evidence to support it.
However skeptical some biologists are of the date, they were impressed by the scope of the canine study, which is believed to be the largest of its kind. Stephen O'Brien, chief of the Laboratory of Genomic Diversity at the National Cancer Institute in Maryland, said the study was "absolutely great. It's first rate."
The physical evidence of fossilized bones and skulls suggests that dogs as they are known today first appeared about 14,000 years ago. Domestic cats appeared as recently as 7,000 years ago. Most modern dog breeds are at most a few centuries old.
Most researchers therefore deduced that animals were first tamed and domesticated between 10,000 and 14,000 years ago, about the time humans started building walled cities, planting crops and mastering irrigation.
But the techniques of molecular genetics, which can reconstruct and time the biological descent of animals alive today, tell a different shaggy dog story.
Wayne and his colleagues studied the regular clocklike evolution of genetic material contained in the cell's energy-producing complexes called mitochondria, which are inherited through maternal ancestors.
Mitochrondrial DNA changes at a relatively constant rate, and the number of changes increases with time.
The UCLA team analyzed the genetic lineage of 162 wolves drawn from 27 places around the world and of 140 dogs belonging to 67 breeds, including golden retrievers, German shepherds, collies, fox terriers, St. Bernards, poodles, bulldogs, Rottweilers, sheep dogs and chow chows. They also analyzed five coyotes and 12 jackals.
To determine how long ago dogs emerged, the researchers looked at the DNA sequences from a control region of the mitochondrial genome that has a very high mutation rate--the same molecular clock used by other scientists to trace the descent of human beings to early African ancestors.
The scientists were surprised by the enormous diversity of the genetic sequences they found in dogs--far more than could have evolved in a mere 14,000 years, Wayne said.
Based on differing estimates of how quickly those mutations could accumulate, the researchers concluded that dogs could have originated as long as 135,000 years ago or as recently as 60,000 years ago.
Wayne suggested that the reason there are no fossils of dogs from that period may be because the first dogs physically resembled wolves for much of their early history and were not bred by their human masters for different characteristics until relatively recently.
What primitive hunter would dare domesticate a wolf? There is considerable evidence that wolves and early humans lived in the same areas. Bones of wolves have been found in the same area as remains of early human species up to 400,000 years ago.
Wayne said the genetic evidence suggests that humans may have tamed members of that progenitor species at least twice, but that it was a nonetheless rare event.