What the evolutionary history of the dog tells us about another animal: ourselves. From a cave in France, a new picture has emerged of canines as our prehistoric soulmates.
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Ross MacDonald
Chauvet Cave in southern France houses the oldest representational paintings ever discovered. Created some 32,000 years ago, the 400-plus images of large grazing animals and the predators who hunted them form a multi-chambered Paleolithic bestiary. Many scholars believe that these paintings mark the emergence of a recognizably modern human consciousness. We feel that we know their creators, even though they are from a time and place as alien as another planet.
Dog historian Mark Derr discusses the story of how man's best friend came to be and how new scientific findings are changing our preconceived notions of the domesticated dog. He speaks with WSJ's Christina Tsuei.
What most intrigues many people about the cave, however, is not the artwork but a set of markings at once more human and more mysterious: the bare footprints of an 8- to 10-year-old torch-bearing boy left in the mud of a back chamber some 26,000 years ago—and, alongside one of them, the paw print of his traveling companion, variously identified as a wolf or a large dog.
Attributing that paw print to a dog or even to a socialized wolf has been controversial since it was first proposed a decade ago. It would push back by some 12,000 years the oldest dog on record. More than that: Along with a cascade of other new scientific findings, it could totally rewrite the story of man and dog and what they mean to each other.
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Getty Images Wolf
For decades, the story told by science has been that today's dogs are the offspring of scavenger wolves who wandered into the villages established by early humans at the end of the last ice age, about 15,000 years ago. This view emphasizes simple biological drive—to feed on human garbage, the scavenging wolf had to behave in a docile fashion toward humans. And—being human—we responded in kind, seeking out dogs for their obsequiousness and unconditional devotion.
As the story goes, these tame wolves bred with other tame wolves and became juvenilized. Think of them as wolves-lite, diminished in strength, stamina and brains. They resembled young wolves, with piebald coats, floppy ears and shorter, weaker jaws. Pleading whiners, they drowned their human marks in slavish devotion and unconditional love. Along the way, they lost their ability to kill and consume their prey.
But it was never clear, in this old account, just how we got from the scavenging wolf to the remarkable spectrum of dogs who have existed over time, from fell beasts trained to terrorize and kill people to creatures so timid that they flee their own shadows. The standard explanation was that once the dump-diver became a dog, humans took charge of its evolution through selective breeding, choosing those with desired traits and culling those who came up short.
Getty Images German Shepard
This account is now falling apart in the face of new genetic analyses and recently discovered fossils. The emerging story sees humans and proto-dogs evolving together: We chose them, to be sure, but they chose us too, and our shared characteristics may well account for our seemingly unshakable mutual intimacy.
Dogs and humans are social beings who depend on cooperation for their survival and have an uncanny ability to understand each other in order to work together. Both wolves and humans brought unique, complementary talents to a relationship that was based not on subservience and intimidation but on mutual respect.
It seems that wolves and humans met on the trail of the large grazing animals that they both hunted, and the most social members of both species gravitated toward each other. Several scholars have even suggested that humans learned to hunt from wolves. At the least, camps with wolf sentinels had a competitive advantage over those without. And people whose socialized wolves would carry packs had an even greater advantage, since they could transport more supplies. Wolves benefited as well by gaining some relief from pup rearing, protection for themselves and their offspring, and a steadier food supply.
The relationship between dogs and humans has been so mutually beneficial and enduring that some scholars have suggested that we—dog and human—influenced each other's evolution.
The Chauvet Cave "dogwolf"—the term I use for a doglike, or highly socialized, wolf who kept company with humans—is controversial, but it cannot easily be dismissed. Over the past three years, it has been grouped convincingly with a number of similar animals that have been identified in Belgium, the Czech Republic, Ukraine and the Altai Mountains in Southern Siberia, dating from 33,000 to 16,000 years ago.
Identification of these early dogs, combined with recent genetic evidence and a growing understanding of animals not as stimulus-response machines but as sentient beings, has broken the consensus model of dog domestication—leaving intact little more than the recognition of the grey wolf, Canis lupus, as progenitor of the dog. Everything else, it seems, is up for grabs.
Getty Images Border Collie
According to the old view, the dog arose around 15,000 years ago in the Middle East. (Or in China, south of the Yangtze River, an alternate possible origin point added in the last decade in an attempt to reconcile archaeological evidence with emerging DNA evidence.)
The first major challenge to the consensus came in 1997, when an international team of biologists published a paper in the journal Science placing the origin of the dog as early as 135,000 years ago. Their date was based on analysis of mitochondrial DNA, which is passed on to offspring through females and is believed to change little from generation to generation; it allows scientists to calculate the time when populations or species separated genetically. This analysis suggested that wolves could have become dogs wherever in Eurasia they associated closely with early humans, and that even after the split was made, dogs and wolves continued to interbreed.
In short, because of their natural affinities, wherever and whenever wolves and humans met on the trail, some of them began to keep company. Often, when socialized wolves died, there were no others immediately available to replace them. But sometimes several socialized wolves would mate or a socialized female would mate with a "wild" wolf and then have her litter near the human camp. The pups would stay or go, according to their natures. This kind of arrangement could have continued for a considerable period. Any number of them could ultimately have produced dogwolves or dogs. Most of those lines would have vanished over time.
The DNA evidence remained controversial for years, even as most major studies placed the genetic separation of wolf and dog at earlier dates than those favored by archaeologists. Hard proof was slow to appear. The Chauvet Cave paw print once provided the only physical evidence for the existence of dogs before 15,000 years ago—and it was, at best, an indirect piece of support.
Then in 2008, Mietje Germonpré, a paleontologist at the Royal Belgian Institute of Natural Science and the leader of an international team of scientists, re-examined fossil material excavated from Goyet Cave in Belgium in the late 19th century and announced the identification of a 31,700-year-old dog, a large and powerful animal who ate reindeer, musk oxen and horses. The dogwolf from Goyet Cave was a creature of the Aurignacian culture that had produced the art in Chauvet Cave.
Last July, another international team identified the remains of a 33,000-year-old "incipient dog" from the Altai Mountains in southern Siberia. This month, Ms. Germonpré confirmed another find, this one in the Czech Republic, of the remains of a 26,000- to 27,000-year-old dog that had been buried with a bone in its mouth—perhaps to fuel it as it accompanied its human companion to the afterlife.
While the old consensus model held that the first dogs were small, these and other recently identified early dogs are large animals, often with shorter noses and broader faces than today's wolves. These early dogs appear in the camps of hunters of horses, reindeer, mammoths and other big game. From all appearances, they were pack animals, guards, hunters and companions. They are perhaps best viewed as the offspring of highly socialized wolves who had begun breeding in or near human camps.
Our view of domestication as a process has also begun to change, with recent research showing that, in dogs, alterations in only a small number of genes can have large effects in terms of size, shape and behavior. Far from being a product of the process of domestication, the mutations that separated early dogs from wolves may have arisen naturally in one or more small populations; the mutations were then perpetuated by humans through directed breeding. Geneticists have identified, for instance, a mutation in a single gene that appears to be responsible for smallness in dogs, and they have shown that the gene itself probably came from Middle Eastern wolves.
All of this suggests that it was common for highly socialized wolves and people to form alliances. It also leads logically to the conclusion that the first dogs were born on the move with bands of hunter-gatherers—not around semi-permanent pre-agricultural settlements. This may explain why it has proven so difficult to identify a time and place of domestication.
Taken together, these recent discoveries have led some scientists to conclude that the dog became an evolutionary inevitability as soon as humans met wolves. Highly social wolves and highly social humans started walking, playing and hunting together and never stopped. The dog is literally the wolf who stayed, who traded wolf society for human society.
Humans did wield a significant influence over dogs, of course, by using breeding to perpetuate mutations affecting their shape, size and physical abilities. Recent studies suggest that the dog has unique abilities among animals to follow human directions and that its capacity for understanding words can approach that of a two-year-old child. To various degrees, humans appear to have concentrated those and other characteristics and traits through selective breeding.
Since the advent of scientific breeding in the late 18th century, humans have altered the look and temperament of the dog more than they had over thousands of preceding years. A team of gene-sequencers at the Broad Institute of Harvard and the Massachusetts Institute of Technology estimated that the dog lost 4% of its genetic diversity during its initial separation from the wolf. Much greater losses have occurred as a result of modern breed formation, one result of which is the more than 400 inheritable diseases to which purebreds are uniquely vulnerable.
Recent genetic evidence has confirmed that certain basic types—pariah dogs, sight hounds, mastiffs, spitz-type dogs and small dogs—arose very early in the transformation of wolf to dog. These dogs adapted to their homelands and often had special talents as hunters, guards and eventually herders. These characteristics were often perpetuated over time.
Scientific breeders believed they could improve on nature by consolidating several similar types into one breed or isolating a few prize specimens from a larger population. In both cases, they relied on inbreeding to create and perpetuate the look and talents they wanted. With the advent of kennel clubs in the mid-19th century, the pace of breed creation picked up.
Breeders began to create dogs to fit the needs of the wealthy—from sporting dogs that could point and retrieve fowl, to little puppy-like lap dogs. The dog proved to be a wonderful animal for testing the skill of breeders, since it could be stretched in size from two to 200 pounds.
Purebred dogs were expensive commodities until after World War II, when they became symbols of arrival in the middle class. Increased demand led to increased breeding, often in puppy mills. The resulting dogs had health and behavior problems from bad breeding and the poor care of pregnant females and newborn puppies.
In some cases, the traits that breeders desire are inherited along with unwanted, debilitating conditions—such as when blindness and epilepsy accompany particular coat styles and eye colors. In many regards, the original, naturally occurring breeds were healthier and better at their appointed tasks than their purebred heirs.
But this is just the most recent chapter of a long tale. The tableau in the mud of Chauvet Cave is a stark reminder that dogs and humans have traveled together for tens of thousands of years, from ancient hunting camps to farms, ranches cities and suburbs—from the tropics to the poles. The relationship has endured not because dogs are juvenilized wolves but because they are dogs—our faithful companions.
—Mr. Derr's most recent book is "How the Dog Became the Dog: From Wolves to Our Best Friends."
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的重要動力。她有先知的勇氣與觸角。她是一位非凡的女性!
