By Christine Mlot
As ecologist at the Savannah River Site near Aiken, SC, I. Lehr Brisbin, Jr. keeps close tabs on the wildlife in the 300-square-mile spread surrounding the Department of Energy’s nuclear facility. Beginning in the 1970s. in the course of routine monitoring of animals for radioactive contaminants, he occasionally came across wild dogs roaming the wild savannsa or nosing around the dumpsters.
The dogs all seemed to be of a certain
type: slightly shy with a medium build, foxlike face, large upright ears,
and crook tail. With their tawny coats, the dogs could have stood in for
Old Yeller, the quintessential canine of the rural South.
He also thinks there is something even more unusual about the dogs. They bear a strong resemblance to the dingo, the wild and ancient dog of Australian aborigines. Dingos and certain other Asian canines share with the Carolina Dog the ginger-colored coat, which Brisbin says is a hallmark of a very ancient lineage. They also share an enthusiasm for scavenging.
The Carolina Dogs, Brisbin suspects, may be North America’s most primitive dog, representative of, if not closely related to, the domesticated canines that accompanied nomads across the Bering Strait into North America 8,000 years ago.
Brisbin, who writes about primitive dogs and the importance of understanding the dog’s origins in the April 15, 1997 Journal Of The American Veterinary Medical Association, cautious that his interpretation is a hypothesis. The Carolina Dogs could simply be a more recently isolated population of European descent or other canine stock. Genetic analyses are under way to help clarify how distinctive the animals are and how they fit into the worldwide story of people and dogs.
People have long wondered about the circumstances
that led prehistoric dogs to come, sit, and permanently stay, thus creating
the first human-animal bond. Researchers have generally based their
interpretation of the origins of the domesticated dog on archaeological
records. In the past decade, however, molecular biologists have started
to study canine DNA to trace the complex ancestry of the more than 400
dog breeds and related canine species.
That conclusion has raised some hackles.
“I’m flabbergasted.” says Brisbin.
“It’s bound to be controversial because it’s such an earlier date.” says Marion Schwartz of Yale University. Schwartz’s book, A History of Dogs in the Early Americas (Yale University Press), was released this month.
Other researchers find the result convincing, however surprising. The report “has really very compelling data.” says Elaine Ostrander, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle who is collaborating on a study of the dog genome. “It’s a fascinating and exciting story.
Even the fossil record has triggered
crashes of opinion. Fossil bones of dogs have been found along with
human remains in caves around the world. Arguments have been made
that clogs first became domesticated in the Middle East, Europe, or various
sites in Southeast Asia.
Many researchers supposed that these
early dogs were descendants of tamed wolves, which interbred and evolved
into a domesticated species. Other scientist suspect that jackals or coyotes
contributed to the dog’s ancestry.
The team collected either blood samples or hairs from all of the animals, then extracted DNA from those samples. DNA mutates over generations, and researchers use these changes to gauge the amount of time during which a lineage has evolved separately. The more similar two related sequences are, the less time the DNA molecules have had to mutate and the more recently the two species diverged.
Wayne and his colleagues looked at a segment of the cells’ mitochondrial DNA, which is separate from the main chromosomal DNA. Mitochondrial DNA mutates rapidly, making it useful for timing the evolutionary divergence of closely related species like dogs and wolves.
Based on the DNA sequences, most of the dogs could be assigned to one of four groups. The largest and most diverse group contains sequences found in the ancient dog breeds, including the dingo and the New Guinea singing dog, along with many modern breeds, such as the collie and retriever.
Other groups contained sequences taken from the elkhound and German shepherd, for example-that were more closely related to certain wolf sequences than to those of the main dog group, bolstering the notion that dogs may have been domesticated from wolves several times. It’s also possible, says Vila, that domestication happened once, after which domesticated dogs bred with wolves from time to time. What seems impossible, says Vila, is that all the DNA variability evolved in the time frame usually assigned to domestication. “We have found so many differences in the DNA that the [dog’s] origin cannot be 14,000 years ago,” one of the commonly assigned dates for domestication. That assumes, however, that the evolution of the small segment of DNA gauges accurately what was happening to the species overall. Such molecular clocks have been controversial says Vila.
The researchers do have an explanation
for the older time frame that makes good sense. Ostrander says.
Although the fossil record for dogs becomes obscure beyond about 14.000
years ago, there are fossils of wolf bones in association with early humans
from well beyond 100.000 years ago.
Once people settled and started to farm,
they might have begun selectively breeding their wolf-dogs into herders,
guards, and different kinds of hunters.
The little-known Carolina dog was not included in the large analysis by Wayne’s group. The genetic analysis that’s been done on the breed so far hasn’t clarified its pedigree. William F. Gergits of Therion Corp. in Troy, NY, has found that at least one genetic marker present in dingos and other primitive dogs is missing in the Carolina dog.
Schwartz says that the dogs probably aren’t direct descendants but are “very similar to types of dogs Native Americans would have had in that part of the country.’ She adds, ‘they do seem to be more primitive-what I think of as a basic dog.’ The primitive dog that hung around Native Americans all but disappeared through interbreeding with European arrivals, says Schwartz, and probably with wolves and coyotes.
Still, the basic dog lurks in the gene pool of today’s highly bred pet, as compelling to people in postmortem times as it was in the Pleistocene.