Science & History
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That the dog is descended from the wolf—or more precisely, the wolf who stayed—is by now an accepted fact of evolution and history. But that fact is about all that is agreed to among the people who attempt to answer fundamental questions about the origins of the dog—specifically, the who, where, when, how and why of domestication.
Dates range from the dog’s earliest appearance in the archaeological record around 14,000 years ago to the earliest estimated time for its genetic sidestep from wolves around 135,000 years ago. Did the dog emerge in Central Europe, as the archaeological record suggests, or in East Asia, where the genetic evidence points? Were they tame wolves whose offspring over time became homebodies, or scavenging wolves whose love of human waste made them increasingly tame and submissive enough to insinuate themselves into human hearts? Or did humans learn to follow, herd and hunt big game from wolves and in so doing, enter into a complex dance of co-evolution?
Despite the adamancy of adherents to specific positions, the data are too incomplete, too subject to wildly different interpretations; some of the theories themselves too vague; and the physical evidence too sparse to say with certainty what happened. Nonetheless, some models—and not necessarily the most popular and current ones—more clearly fit what is known about dogs and wolves and humans than others. It is a field in high flux, due in no small measure to the full sequencing of the dog genome. But were I a bettor, I would wager that the winning view, the more-or-less historically correct one, shows that the dog is the result of the interaction of wolves and ancient humans rather than a self-invention by wolves or a “conquest” by humans.
Our views of the dog are integrally bound to the answers to these questions, and, for better or worse, those views help shape the way we approach our own and other dogs. It is difficult, for example, to treat as a valued companion a “social parasite” or, literally, a “shit-eater.” To argue that different breeds or types of dogs represent arrested stages of wolf development both physically and behaviorally is not only to confuse, biologically, description with prescription but also to overlook the dog’s unique behavioral adaptations to life with humans. Thus, according to some studies, the dog has developed barking, a little-used wolf talent, into a fairly sophisticated form of communication, but a person who finds barking the noise of a neotenic wolf is unlikely to hear what is being conveyed. “The dog is everywhere what society makes him,” Charles Dudley Warner wrote in Harper’s New Monthly Magazine in 1896. His words still hold true.
Since the dog is both a cultural and a biological creation, it is worth noting here that these opposing views of the dog’s origin echo the old theory that the sniveling, slinking pariah dogs and their like—“southern breeds”—derived from jackals, while “northern breeds”—Spitz-like dogs and Huskies—descended directly from the wolf. Darwin thought as much, so did the pioneering ethologist Konrad Lorenz until late in his life, when he accepted that the wolf was the sole progenitor of the dog. In the theories of Raymond Coppinger and others—and I think this transference is unconscious—the scavenging jackal becomes a camp-following, offal-eating, self-domesticating weenie of a tame wolf. In turn, those wolves become the ur-dog, still manifest in the pariahs of India and Asia, from which the dog we know is said to have emerged. It’s a tidy, convenient, unprovable story that has an element of truth—dogs are accomplished scavengers—but beyond that, it is the jackal theory with a tattered new coat. In dropping humans from the process, the scavenging, self-domesticating wolf theory ignores the archaeological record and other crucial facts that undercut it.
Fossils found at Zhoukoudian, China, have suggested to archaeologists such as Stanley Olsen, author of Origins of the Domestic Dog, that wolves and Homo erectus were at least working the same terrain as early as 500,000 years ago. The remains of wolves and Homo erectus dating to around 300,000 years ago have also been found in association with each other at Boxgrove in Kent, England, and from 150,000 years ago at Lauzerte in the south of France. It seems more likely that this omnivorous biped, with its tools and weapons, lived and hunted in proximity to that consummate social hunter, the wolf, through much of Eurasia, than that their bones simply fell into select caves together. Who scavenged from whom, we cannot say.
Wolves were far more numerous then than now, and they adapted to a wide range of habitats and prey. On the Eurasian steppes, wolves learned to follow herds of ungulates—in effect, to herd them. Meriwether Lewis observed the same behavior during his journey across North America in the opening years of the 19th century; he referred to wolves that watched over herds of bison on the Plains as the bisons’ “shepherds.” Of course, those “shepherds” liked it when human hunters attacked a herd because they killed many more animals than the wolves, and although the humans carried off the prime cuts, they left plenty behind.
Ethologists Wolfgang M. Schleidt and Michael D. Shalter refer to wolves as the first pastoralists in “Co-evolution of Humans and Canids,” their 2003 paper in the journal Cognition and Evolution. Early humans, they argue, learned to hunt and herd big game from those wolves; thus, the dog emerged from mutual cooperation between wolves and early humans, possibly including Neanderthal. There is no evidence yet of Neanderthal having tame wolves, much less dogs, but the larger point is that when modern humans arrived on the scene, they found wolves already tending their herds, and they immediately began to learn from them. That was long before humans began, in some parts of the world, to settle into more permanent villages, some 12,000 to 20,000 or 25,000 years ago.
Schleidt and Shalter based their model on wolf behavior and on genetic studies that have consistently shown that dogs and wolves diverged between 40,000 and 135,000 years ago. The first of those studies emerged from the lab of Robert K. Wayne, an evolutionary biologist at the University of California at Los Angeles who had already made headlines by showing definitively that the dog descended from the wolf alone. In a paper appearing in the June 13, 1997, issue of Science, Wayne and his collaborators said that dogs could have originated around 135,000 years ago in as many as four different places. They also argued that genetic exchanges between wolves and dogs continued—as they do to this day, albeit in an age during which dogs have become ubiquitous and wolves imperiled.
Since that paper appeared, the dog genome has been fully sequenced and provides a time frame for domestication of 9,000 generations, which the authors of a paper on the sequencing in the December 8, 2005, issue of Nature pegged at 27,000 years. But except for that, subsequent studies of mitochondrial DNA, which is most commonly used to date species divergence, have pointed to a time frame of 40,000 to 135,000, with 40,000 to 50,000 years ago looking like the consensus date.
Most of this work has been conducted in Wayne’s lab; in the Uppsala University lab of Carles Vilà, his former student and the lead researcher on the 1997 paper; and in the lab of Peter Savolainen of the Royal Institute of Technology, Stockholm, another collaborator on the original paper.
A signal problem with the early date is that it doesn’t appear to match the archaeological record. The dog is not only behaviorally but also morphologically different from the wolf, and such an animal first appears in the fossil record around 14,000 years ago in Bonn-Oberkassel, Germany. Archaeologists nearly universally peg the origin of the dog to that time.
Wayne, Vilà and their supporters have suggested from the start that behavioral change could predate morphological change, which would have occurred when humans began to create permanent settlements, thereby cutting—or at least reducing—their wolf-dogs’ contact with wild wolves. People might also have begun attempting to influence the appearance of their dogs at this point.
But those Germans get in the way again. Bonn-Oberkassel, site of the consensus first fossil dog, is not a permanent settlement.
Trying to square genetic and archaeological dates, Peter Savolainen resurveyed the mitochondrial DNA of dogs and wolves, recalibrated the molecular clock and proposed in a paper in Science, November 22, 2002, that the dog originated in East Asia 15,000 to 40,000 years ago. It was a good try, but now it appears that his “40,000 years ago” date was more accurate. Also, the earliest known dog appears in Germany, not East Asia, a region to which other genetic evidence points as well.
In many ways, the dispute over dates and places is just a precursor for the debate over how that happened. Archaeologists and evolutionary biologists who want the first dogs to look like dogs have tended to argue that the transition is a result of a biological phenomenon called “paedomorphosis.” That basically means that the animal’s physical development is delayed relative to its sexual maturation. It produces dogs with more domed heads; shorter, broader muzzles; and overall reduced size and slighter build than a wolf. Accelerated physical development relative to sexual maturation (hypermorphosis), on the other hand, produces dogs larger than the progenitor wolf.
When maturation is stopped early enough, the resulting animal is said to resemble a “neotenic,” or perpetually juvenilized, wolf. Coppinger and others have carried the argument further to argue that behaviorally, the dog resembles a neotenic wolf, with some breeds being more immature or less developed than others. There is general agreement that, beginning in the late 19th century when the dog began to move into the city as a pet, breeders sought to soften and humanize the appearance of some breeds to make them look like perpetual puppies. But beyond that, it is more correct to view the dog as an entity different from the wolf.
Currently, many researchers like to invoke an experiment in domestication launched in 1959 at the Institute of Cytology and Genetics in Novosibirsk, Siberia, by Dmitry Belyaev and continued after his death by Lyudmila Trut and her colleagues. Belyaev selectively bred foxes for “tameness” alone, defined as their level of friendliness toward people. He ended up with foxes that resembled dogs. A number of them had floppy ears, piebald coats, curly tails and a habit of submissively seeking attention from their human handlers with whines, whimpers and licks. (I wouldn’t want such a dog.)
Anthropologist Brian Hare tested the tame foxes in 2004 and found that they, like dogs, had the capacity to follow a human’s gaze, something wolves and wild foxes, not to mention chimpanzees, won’t do.
A number of researchers have embraced these tame foxes as a template for dog domestication. While they doubtless cast insight on the problem, I doubt that they will answer all questions. Arguments by analogy are suspect science and should be even more so in this case, since the selection criteria for these foxes were also against aggression—hardly the case for dogs—and foxes clearly are not wolves.
That said, the experiment does appear to confirm that selective breeding for behavior alone can also produce morphological changes similar to what the wolf experienced in becoming a dog.
Coppinger has invoked the fox experiment to support his theory that wolves that became dogs self-domesticated. As humans in some areas moved into permanent settlements, their refuse heaps became feeding grounds for wolves who were tame enough—or least-frightened enough—to feed near humans. Subsequent generations became more tame, and people began to allow them to wander their camps, eating feces, hunting rodents. From that group, people took some animals for food. Then, when the animals were thoroughly self-tamed, people began to train them to more wolfish behaviors, like hunting.
What he and others overlook in citing the fox experiment is that those animals were subjected to intense artificial selection by people. They also ignore the fact that the first dog appears in a seasonal camp, not a permanent settlement.
In their book, Dogs, Coppinger and his wife, Lorna, argue that these early protodogs would have resembled the ownerless dogs of Pemba Island, a remote part of the Zanzibar archipelago. As a model, Pemba suffers numerous problems, as does Coppinger’s theory. It is an Islamic island, and Islam has scarce place for dogs, believing them filthy, largely because they scavenge and eat excrement.
Beyond that, Pemba was a wealthy island in the 18th and 19th centuries due to its clove plantations, which were worked by African slaves and overseen by Arabs. The plantations have long since fallen into disrepair, on an island populated by the descendants of free slaves, where poverty is the rule. Attempting to read the past by looking at the present is a well recognized form of historical fallacy. It can’t be done, especially in a place where there is no strong cultural tradition.
Elsewhere in the developing world, free-ranging dogs are often more than scavengers or food. Some are fed; they protect territories or vendors’ carts. A few might be taken in, but, again, these dogs must be studied and understood in their current context and then placed in a broader historical context, if possible.
Moreover, Coppinger ignores the entire tradition of dogs and people in Europe, Japan and Korea—wherever dogs were employed from an apparently early date for a purpose, including companionship and ritual. Archaeologist Darcy F. Morey clearly demonstrated in the February 2006 issue of The Journal of Archaeological Science that people have been burying dogs and treating them with reverence and respect from the beginning, hardly the fate of scavengers.
People will argue, but I think the question of whether the dog is a juvenilized wolf is best answered with this observation: The dog follows human gaze, according to Hare, and is so attentive to people that it can imitate them, according to Vilmos Csányi, and it does so from an early age. No wolf of any age can replicate that basic behavior. It is far better to look at the dog as a differently developed wolf than as a developmentally retarded wolf.
Similarly, until shown otherwise, it seems more accurate to view domestication as a dynamic process involving wolves and people. At a time when the boundaries between human and wild were much more porous than now, people doubtless took in animals, especially young animals of all kinds, especially wolf pups, since in many places, they were hunting the same game and perhaps scavenging from each other.
As those pups matured, they returned to the wild to breed, with the naturally tamest among them denning close to the camp where they had been raised and, yes, could scavenge. Over the past year, researchers have shown that the area of the brain known as the amygdala is quite active when “fear of the other” begins to develop. In 2004, a team of researchers from Uppsala University, including Vilà, reported in the journal Molecular Brain Research on changes they had found in gene expression in the frontal lobe, hypothalamus and amygdala of wolves, coyotes and dogs. More than 40 years ago, J.P. Scott and John L. Fuller showed that the dog pup had a lengthened socialization period before fear of the other set in, compared with the wolf pup.
No one knows how fast the change happened, but in some places, tame wolves—dogs—resulted from this process. They provided territorial defense, helped with hunting (which they do well), scavenged, and were valued for companionship and utility. Some could be trained to carry packs. That early dog probably remained nearly indistinguishable from the wolf except in places where their gene pool became limited by virtue of some isolating event. The smaller gene pool forced inbreeding that, along with changing environmental conditions, somehow “destabilized” the genome.
Vilà and two colleagues suggested in an article published online on June 29, 2006, in Genome Research, that domestication relaxed “selective constraint” on the dog’s mitochondrial genome, and if that relaxation extended to the whole genome, as it appeared to, “it could have facilitated the generation of novel functional genetic diversity.”
European and North American breeders have taken full advantage of that or some other mechanism to create the most morphologically diverse mammal around. But other cultures did not follow that path.
There are other theories afloat in what is an exciting time for people who study dogs. But the one that succeeds will reflect the dynamic relationship between human and dog.
Illustration by Amadeo Bachar