Domestication of the Dog, Part II, The

Phi Kappa Phi Forum, Winter 2005 by Tiffany-Castiglioni, Evelyn

In my previous column (Summer 2004) I discussed how all modern domestic dogs can trace their origins from ancestral Eurasian wolves fifteen-thousand years ago. I also discussed the farm-fox experiment, which was a reenactment of how domestication may have taken place. In the fox experiment, researchers showed how wild silver foxes, selectively bred over thirty-five generations and forty years for the sole trait of friendliness to humans, became more dog-like animals. These so-called "domestic elite" foxes are not only friendly to humans and seek human attention, but some of them also have new physical traits that have appeared in parallel with the selection for tameness, even though the physical traits were not selected for per se. These traits include spotted or black-and-white coats, floppy ears, tails that curl over their backs, and earlier sexual maturity. In this column I shall discuss a speculative view on how humans and the wolves that became proto-dogs may have interacted at the dawn of domestication, how domestication has been taken one step further through the creation of breeds, and how purebred dogs are not just attractive and intelligent (many of them) but are golden right down to their very genes.

CLEVER ANCESTORS, HUMAN AND CANINE

Fifteen thousand years ago dog domestication was probably not so concentrated or focused an endeavor as the farm-fox experiment, but humans had to have been ready for it. The people who domesticated dogs must have had a society in which a long-term project of this kind could be supported and passed on to ensuing generations, even without the advantage of written records. They must have had some understanding that traits are inherited and must have been able to keep wild wolves from breeding with their proto-dogs. They also must have placed great value in the dog to invest their time and resources into its breeding.

Possibly they had some partially tame wolves to work with, such as self-selected wolves that found an ecological niche as scavengers on the outskirts of settlements. According to Dr. Raymond Coppinger (Hampshire College, Massachusetts), such wolves may have been less fearful of humans than most wild wolves, and this trait must have been inheritable, making these wolves more amenable to domestication. The wolves hypothetically separated into two populations, the village-oriented scavengers and the packs of hunters. The next steps have not been defined, but selective pressure must have been present to sustain the divergence of these populations. At some point, conditions under which social bonds could form between pups and humans, perhaps while the pups were still of nursing age, must have developed. That is an uncomfortable number of "must-haves," but research has not yet shed further light on this aspect of our remarkable pre-history.

The wolf-as-camp-follower hypothesis is unfortunately difficult to test and is supported primarily by observations that in some parts of the world, dogs live as locally adapted village scavengers. However, it may be of value to study other urbanized canids, such as urban coyotes that have become increasingly present as scavengers in Los Angeles and Vancouver for two or three decades. Anecdotal observations indicate that these animals are less fearful of humans than are coyotes remaining in the wild. Is this an example of individual adaptation, or are populations of animals undergoing genetic selection for tolerance to humans? Do they pass these traits on to their offspring? I have been unable to locate any research in this area. What an intriguing project for an evolutionary genomicist, an animal behaviorist, and an ecologist.

The fact remains that our human forebears and dogs' wolf forebears were both resourceful organisms who established a commensal relationship that has endured over millennia. The relationship is still evolving, and with recent revelations from canine genomics, it is evolving in unexpected ways. Not content with the basic dog, humans took to artificial selection for creating races or breeds of dogs with specific appearances, behaviors, and dispositions. More than four hundred breeds, one hundred and fifty of which are recognized by the American Kennel Club, have been created by generations of tightly regulated breeding to a breed standard, mostly in the last one hundred to five hundred years. No other animal seems to have been subject to as much intentional selection as the dog. While purebred dogs were initially bred for specific working behaviors, they are now more commonly bred for desired appearance and temperament, and the job title held by most purebred dogs is "companion and pet." However, their service to humans may expand after the publication in May 2004 of the first detailed genetic comparison of purebred dogs. A serendipitous offshoot of creating dog breeds seems to be new models for human hereditary diseases.

ADDING TO THE DOG'S RÉSUMÉ

Dr. Elaine A. Ostrander and Dr. Leonid Kruglyak (Science, Vol. 304, p. 1160; 2004) at the Fred Hutchinson Cancer Research Center in Seattle found that by comparing genetic information among eighty-five dog breeds, they could discover the genetic and evolutionary relationships among breeds. Breeds are revealed to have the same genes but with variants in DNA sequence that are breed-specific. In this respect, dog breeds are even more distinct than are human populations that have evolved on different continents. Surprisingly, the dogs with the closest genetic relationship to ancestral wolves are several ancient Asian breeds, including the unlikely Sharpei, a medium-sized, broad-muzzled dog that looks like it is wearing a much larger dog's skin. In contrast, the Pharoah Hound and Ibizan Hound, which resemble pictures on ancient Egyptian tomb walls, turn out to be modern recreations of the body type from other breeds. Dr. Ostrander's larger message, however, is the usefulness of purebred dogs in the study of hereditary diseases. Various breeds have distinct hereditary health problems. Breeding records have been kept on many breeds for decades. Therefore, purebred-dog populations may be useful for identifying specific genes associated with diseases that affect both dogs and humans, such as cancer, epilepsy, and heart disease.