Biologists, if they weren't victims of the same blindness that afflicts us all, wouldn't hesitate to classify dogs as social parasites. This is the class of manipulative creatures exemplified by the cuckoo, which lays its eggs in the nest of some poor unsuspecting dupe of a bird of another species. The befuddled parents see a big mouth crying out for food and stuff it full of worms at the expense of their own offspring. Every time they turn their backs, the cuckoo hatchling shoves another of their own flesh and blood overboard. The parents never seem to notice.
Dogs have not quite reached that point in their parasitism of human society. Still, it is sobering that the No. 1 behavioral problem that drives dog owners to seek professional help is aggression. And canine aggression is most often directed at children. In 1996 dog attacks cost U.S. insurance companies $250 million in claims paid out, with total costs to society estimated at $1 billion a year. By dog standards, though, a billion is nothing when it comes to diverting the wealth of one's best friends; Americans spend more than $5 billion a year on dog food and $7 billion on canine veterinary care.
Add up all the benefits that dogs provide us and compare that sum with the costs, and it is not a rational bargain on our part. Dogs are extraordinarily beautiful animals; they are extraordinarily interesting animals too, and as a devoted student of animal behavior, if nothing else, I certainly find the rewards of living with dogs worth the cost. But I am also keenly aware that the conventional explanations of where dogs come from, how they ended up in our homes, and why they do what they do for us have to be all wrong.
In the past couple of years new scientific evidence has started to confirm just how weird the relationship between dogs and human beings is—and how different it is from what we tend to think it is. What truly defines the differences between breeds of dogs, what motivates dogs to be protective or helpful to us, what causes aggressive behavior by dogs toward human beings, why dogs started hanging around us in the first place—when it comes to dogs, almost nothing is what it seems.
The starting point for this scientific reconsideration of matters canine is an extremely modest effort, colloquially known as the Dog Genome Project. In scale it is nothing like the Human Genome Project, a $3 billion federally sponsored program to map every gene in the human body. The dog project will cost a few million dollars, with a lot of the funding coming from private breed clubs that want to develop genetic tests for inborn diseases that their particular breeds are susceptible to.
Finding genes that cause this or that ailment is what most people think of when they think about gene mapping and genetic research, and pinpointing the causes of inborn diseases is certainly one of the obvious and direct payoffs that will come from a better understanding of the dog genome. But the genes an individual carries are more than a personal health chart; they are also a logbook of the evolutionary voyage of the species. The dog's journey through the past 100,000 years in the company of man has left distinctive markers in the genes of the dog population. Just as an archaeologist can deduce nonmaterial attributes of a long-vanished civilization—its social hierarchies, superstitious beliefs, trading patterns—from its material remains, so geneticists can deduce much about the history, evolution, and social ecology of a species from the patterns that all those forces have etched into its genes.
Merely getting to the point where scientists can make a serious study of the dog genome has required something of a breakthrough in the culture of science. For years science has maintained a rather aloof stance toward domestic animals in general, and toward dogs in particular. Traditionally, zoologists have considered domestic animals to be uninteresting, and have generally classed them as "degenerates"—unworthy of ecological scrutiny because they have lost their adaptive behaviors. Veterinary medicine aside, it is as if molecular genetics and the other great advances of twentieth-century science had simply bypassed the dog.
And then there is the fact that scientists can be as sentimental and uncritical about dogs as the rest of humanity seems to be. "Most scientists who talk about dogs have their scientist hat and their dumb hat," says Gustavo Aguirre, a veterinary ophthalmologist at Cornell University's Baker Institute for Animal Health. "And whenever they start talking about dogs, they put on their dumb hat. They say things that as scientists they have to know can't possibly be right." The upshot is that scientists know infinitely more about the genome of the mouse or the sheep or the fruit fly than they know about the genome of the dog; they know infinitely more about the social ecology of the ant or even the wolf than they know about the social ecology of the dog.
A few years ago Aguirre and several others decided to put on their scientists' hats and apply the tools of modern biology to the study of the dog genome. Their motivation was to try to understand the genetic roots of the particularly devastating inborn degenerative diseases that cause certain breeds—notably, miniature poodles, Norwegian elkhounds, Irish setters, collies, and cocker spaniels—to go blind. These diseases, characterized by night blindness followed by progressive deterioration of daytime vision, bear a striking similarity to the human condition known as retinitis pigmentosa.
Studying the causes of canine genetic diseases remains a central aim of their work, but over time the project acquired a broader objective: to construct a rough but comprehensive map of the entire dog genome, and with that to begin to understand what makes a dog be what it is and do what it does.
Aguirre likes to show visitors to his lab the "kennel." This consists of four large stainless-steel chests containing row upon row of frozen blood samples chilled to -80 degrees Celsius. For the genome map the researchers collected samples from 212 dogs representing three generations, all the products of crosses between dogs about as different as possible—poodles, Doberman pinschers, Irish setters, Norwegian elkhounds, and beagles. Fortunately for Aguirre and others in the field, dogs are particularly good for genetic studies. Unlike human beings, who tend to intermarry widely, dog breeds have been kept separate through inbreeding. Norwegian elkhounds, for example, are very different from beagles not only in the way they look and in the inborn diseases they get (beagles almost never suffer from degenerative blindness, for instance) but also in the many random bits of "junk" DNA that are found on every one of their chromosomes. Genes are the sequences of DNA on a chromosome that actually direct the body to do something. But long stretches of DNA between genes have simply accumulated over the course of evolution. Mutations in parts of the genome that do something important are often harmful, and tend to get weeded out of the population quickly, whereas mutations in the junk DNA just pile up, in random variations that can be used to distinguish one family line from another. As far as researchers are concerned, junk DNA sequences have another useful property: they tend to possess distinctive patterns that make it easy to construct a molecular "probe" that zeroes in on them.
What all this means is that researchers can use junk DNA sequences as flags or markers to help them find their way around the genome. If a beagle is crossed with an elkhound and then their offspring are crossed, some of those dogs will suffer from retinal degeneration and some won't. They will also almost certainly have many differences in the easy-to-measure genetic markers they carry. If all disease carriers have marker A at a particular spot on a chromosome whereas no noncarriers do, the disease gene must be close by.
Using this technique, Aguirre's lab and a group led by Elaine Ostrander, at the Fred Hutchinson Cancer Research Center, in Seattle, created the first "linkage" map of the dog genome, which was published in late 1997. The map is made up of about 150 mileposts along the dog genome; each milepost consists of a bit of junk DNA anchored to a gene that remains constant. The gene allows researchers to know where on the genome they are; the variable bits allow them to search for genetic differences between individuals, and so to tie a disease or other physical characteristic to a specific marker.
Another thing that dogs have going for them in terms of genetic mapping is that they produce a lot of offspring—litters of ten are not uncommon. Standard statistical calculations reveal that diseases that are all but impossible to map in human families can readily be mapped in the typical canine family. Already several genes responsible for canine disorders have been pinpointed, and screening tests have been developed for them. The Irish Setter Club of America,which was one of the first to support genetic research on its breed's problems, now has a blood test that it requires for all purebred Irish setters to determine if they are carrying a gene for retinal degeneration.
More-conventional sponsors of scientific research, such as the National Institutes of Health and the American Cancer Society, have begun to fund the study of canine genetics, because dog disease and human disease are turning out to be closely linked. More than twenty inborn diseases in dogs have been traced to specific defective genes; in every case the same defective gene has been found in human beings. Dogs even carry the brca 1gene, which was identified a few years ago as causing a significantly increased risk of breast cancer in women. Probably 90 to 95 percent of the dog genome and the human genome are identical.
From the start dog-genome researchers realized that along the way they might also discover a lot about the history of dogs and their innate behavior—the sorts of things that people who like dogs have always wondered about. No one expects to find a gene for loyalty, but maybe there are genes for herding behavior or retrieving or guarding. And although there is almost certainly not agene, or even a handful of genes, that accounts for the transformation from the wolf to the dog, a study of the population genetics of the two species could potentially speak volumes about the origin and history of domestication.
The standard myth about the origin of the dog is that man found him to be a useful companion and so took him in. Dogs were sentinels or shepherds or they helped in the hunt. The oldest archaeological evidence of dogs with a morphology distinct from that of wolves is from about 12,000 years ago in the Middle East, suggesting an evolution coinciding with the rise of the first agricultural settlements and permanent villages, and pre-dating the domestication of other animals, including sheep and goats, by a few thousand years.
The view that dogs came along at about the same time as human beings settled down is so widespread and so often repeated in standard texts that it is more than a bit surprising to find genetic evidence flatly contradicting it. The evidence comes from a study by Robert Wayne, an evolutionary biologist at the University of California at Los Angeles, who has applied the modern tools of genetic fingerprinting to dogs, coyotes, wolves, and jackals. He and his colleagues collected blood, tissue, or hair samples from 140 dogs of sixty-seven breeds and 162 wolves from three continents. To gauge how closely related these various canines were and when they might have diverged from a common ancestor, the scientists measured differences in their mitochondrial DNA. Mitochondria are like small cells within the cells of animals; they convert stored food into energy with the assistance of oxygen, and they also have the peculiarity—much cherished by geneticists—of reproducing asexually, independent of the rest of the cell. The regular DNA of an animal cell derives equally from both parents. Mitochondrial DNA, however, comes entirely from the mitochondrial DNA of the mother. In normal sexual reproduction genetic change from one generation to the next is very rapid, as the parental genes are mixed and remixed in new combinations. Mitochondrial DNA, in contrast, can change only by mutation, which takes place quite slowly—at a rate of around one or two percent every 100,000 years.
That means that mitochondrial DNA can be used as an evolutionary chronometer. Wolves and coyotes differ by about six percent in their mitochondrial DNA, and, according to fossil evidence, separated from a common ancestor about a million years ago. Wolves and dogs differ by about one percent; using the wolf-coyote time scale, this suggests that they parted company about 135,000 years ago—a lot earlier than the date implied by the first distinctly non-wolflike dog fossil.
Wayne's study also definitively laid to rest an assertion made by both Charles Darwin and Konrad Lorenz—that more than one wild canid species had to have made an appearance in the dog's recent family tree, given the diversity of physical types and behaviors exhibited across the range of modern dog breeds. In fact, long sequences of dog mitochondrial DNA are similar or identical to those in gray wolves, and analysis of the highly variable markers in the regular DNA of dogs and wolves shows a considerable overlap there as well. Jackals and coyotes, though they can interbreed with dogs and produce fertile offspring, possess quite distinct groups of mitochondrial DNA sequences.
The evolutionary chronometer is a measure of ancient origins—it cannot pick up divergence into separate breeding lines that has occurred in the past few hundred years. The most striking discovery Wayne's team made was that there is almost no correlation between a dog's breed and the mitochondrial DNA sequences it carries. In eight German shepherds the scientists found five distinct sequences; in six golden retrievers they found four. And the same sequences repeatedly showed up in many different, and apparently quite unrelated, breeds. The Mexican hairless, or Xolo, a breed known from historical and archaeological records to have existed more than 2,500 years ago in Aztec Mexico—and which presumably separated from Old World breeds some 12,000 years ago, when the Bering land bridge disappeared—contained representatives of all the major mitochondrial DNA sequences found in dogs throughout the world. (The Xolo sequences also resembled those of Old World wolves much more closely than those of New World wolves.)
The point is, then, that if dogs were indeed domesticated more than 100,000 years ago, as Wayne's data suggest, there wasn't much selective breeding going on for most of those 100,000 years. Rather than diverging into separate lines, the dog gene pool remained a well-mixed soup in a bowl of global dimensions. There was considerable gene flow throughout the population, which would not have been the case had early human beings been trying to direct the breeding of their dogs or to develop special lines with certain selected characteristics. Wayne's study also suggests that for a long time the genetic difference between a dog and a wolf was too small to cause any striking morphological change that would show up in the fossil record.
Even if the step from wolf to dog was a small one, it apparently didn't happen very often. Wayne found that the dog mitochondrial DNA sequences fell into four major groups. If there had been a continual influx of new wolf blood into the dog population (that is, if the dog had been reinvented again and again from wild populations at different times), such distinct grouping would not have occurred. Wayne's conclusion is that the earliest dogs "must have been integrated somehow into human society" to keep them genetically isolated from the surrounding population of wild wolves, and also that the domestication of dogs from wild populations must have been "a rare event"—something that happened only a few times in history.
That it happened at a time when "humans were barely human," as Gregory Acland—a veterinarian who works with Aguirre at Cornell's Center for Canine Genetics and Reproduction—puts it, raises an interesting possibility. It suggests that early man may not have sought to domesticate dogs at all. Rather, proto-dog found it in his interest to hang around people, and somehow persuaded them not to throw rocks at him or eat him.
That is a teleological statement, of course; if this scenario is correct, there was no conscious intent on the part of the dogs. But there was arguably little or no conscious intent on the part of the people, either. The wonder and beauty of natural selection is that it is creative; it crafts solutions that for all intents and purposes seem to reflect intelligence—"unthinking" intelligence, as the philosopher Daniel Dennett aptly put it. The evolutionarily correct way to state all this is that human beings, with their campfires and garbage heaps and hunting practices, but above all with their social interactions, represented an ecological niche ripe for exploitation by wolves. Or at least by those wolves that through some chance modification in their genetic makeup were able to exploit that niche and then prospered to pass on those traits to their offspring. Although wolves today are the most widespread wild land mammal in the world—with a range that extends from North America to Europe to Asia, encompassing everything from semi-desert to tundra to subtropical forest—their total population probably numbers no more than 150,000. In the United States there are about 50 million owned dogs and millions more unowned—eloquent evolutionary testimony to the wisdom of mooching off people rather than fighting it out in the wild.
What is so exploitable about human society? And how do dogs manage to exploit it? We are, as the animal behaviorist John S. Kennedy called us, "compulsive" anthropomorphizers—always on the lookout for behaviors that mimic, even superficially, human social phenomena such as loyalty, betrayal, reciprocity. These are useful things to look out for when one is a group-dwelling animal whose survival is threatened less by ravenous wild beasts than by back-stabbing fellow group dwellers. Our cognitive ability to ascribe motives to others is a large part of what makes us human. But it truly is compulsive. Human beings do it so instinctively that they are forever ascribing malignant or benignant motives even to inanimate forces such as the weather, volcanoes, and internal-combustion engines. Our very cleverness is the start of our undoing when we're up against an evolutionary sharpshooter like the dog. We are primed to seize on what are, in truth, fundamental, programmed behaviors in dogs and read into them extravagant tales of love and fidelity. Often dogs need do no more than be their simple selves to amaze and beguile us.
Take the protectiveness that dog owners almost universally impute to their pets. "Protectiveness" is almost certainly nothing of the kind; it is not a sign of a dog's loyalty to and concern for us but an example of what behaviorists call "facilitated aggression." Rather than protecting us, the dog feels protected byus; he is emboldened to react to any threat that appears on his radar screen. Such behavior is observed regularly in wolves: aggression by a dominant member of the pack toward another wolf will trigger an attack by other members.
Or consider the countless stories about dogs that have "saved" people. In fact dogs have no particular instinct to save people and no particular understanding that that is what they are doing even when they do it. Search-and-rescue dogs are trained by exploiting the instinct to retrieve thrown objects. They are trained to fetch. And they are trained to fetch one toy only. Once they master that, they are ready for the next step: A person takes the toy and hides; the dog is encouraged to find—well, his toy. When he finds the "victim," the dog is rewarded by getting his toy. At actual disaster scenes trainers get someone to go and hide with the dog's toy several times a day, so that the dog can score a few successes and not become frustrated.
This takes nothing away from dogs' amazing sense of smell or trainability or utility to humankind in such situations. It does say that what is going on here may be simpler than we are ready to believe. As Gregory Acland points out, "All you're doing is taking a behavior that's there and subverting it." Other "rescuing" behavior in dogs is an even simpler matter. Newfoundlands and other water retrievers will bring anything they can out of the water. Often Newfoundland owners cannot swim with their dogs, because the dogs keep pulling them to shore.
The degree to which seemingly complex behaviors are rigidly and genetically programmed is quite frightening at times—frightening for what it suggests about motivation and free will, at least. Pregnant dogs will often pick up stuffed animals and try to "nurse" them. A cardinal in the wild was once observed feeding goldfish for several weeks; a fish would rise to the surface of the pond and open its mouth, and the cardinal would stuff it full of regurgitated insects. That, of course, is what birds do to feed their young, and apparently all it takes to trigger that behavior is the sight of a gaping mouth.
An early part of Elaine Ostrander's work in the Dog Genome Project was an attempt to locate genes responsible for such complex canine instincts as herding behavior in border collies and the affinity for water in Newfoundlands. The grandpuppies of crosses between border collies and Newfies showed a rich assortment of the two behaviors, enough to make it clear that they were under genetic control—but also enough to show that perhaps a dozen or more genes were involved, and that to accomplish any sort of mapping of those genes, one would need to start with several hundred dogs.
A former postdoctoral research fellow with Ostrander, Melissa Fleming, has developed an assay that attempts to quantify certain innate breed-specific behavioral differences. Fleming found, for example, that border collies would stare at a moving remote-controlled toy car for the duration of a 120-second test. Newfoundlands, in contrast, not only would fail to stare at the car but would not even react to it unless it ran directly into them.
Other studies have turned up some remarkably narrow and distinctive behavioral lineages that further demonstrate the extent to which canine behavior is genetically determined. Certain strains of Siberian huskies and pointers have developed a strongly inherited shyness or aversion to human beings; when kept under identical conditions in identical kennels, the shy dogs will stay back (or, in the case of the pointers, actually freeze and quiver when people approach), while the normal dogs come up to be petted. Breeders have succeeded in producing lines of bloodhounds that bark or do not bark while trailing a scent; of Dalmatians that do or do not take up the proper "coaching" position, trotting under the front axle of a carriage, very close to the heels of the horses; and even of miniature poodles that do or do not "shake hands."
There is probably no "deflecting aggression," or submission, gene, but much of what enables dogs to get away with everything up to and sometimes even including murder in human society is an innate part of wolf social behavior. Dogs are social animals, and so are we. Dog society consists of a strong dominance hierarchy in which submission to and appeasement of higher-ranking animals is necessary to survival. Dominance hierarchies avoid violence for the most part, but the threat of violence is ever present. Thus reading social cues adeptly, down to such details of body language as a flick of the ear or the angle of a tail, is the most basic of canine instincts. "That's what dogs do for a living," Gregory Acland says. "They figure out what's expected of them in a social situation and do it."
Even people who are very bad animal trainers can usually make themselves understood to dogs. If you shout at a dog, it cringes. Does this mean the dog feels sorry for peeing on your Oriental rug? The fact is that it doesn't matter, as far as the dog is concerned, whether he feels sorry or not. The cringe is a successful technique for deflecting aggression. Millions of years of wolf evolution have selected such behaviors because they are socially effective; thousands of years of dog evolution have fine-tuned such behaviors so that they are socially effective on people. Just as we are genetically programmed to seek signs of love and loyalty, dogs are genetically programmed to exploit this foible of ours.
So why are there so many canine misfits around these days? If dogs domesticated themselves, if they have evolved their way into a cozy place in human society by instinctively ingratiating themselves, if they have learned behaviors that elicit a friendly response and play on our preprogrammed sympathies, then why are the veterinary journals full of case reports like this one?
An 18-month-old male Irish Setter was owned by a young childless couple. The husband was often threatened by the dog and had been bitten several times. The dog would growl whenever the husband entered the room. This usually occured if the wife and the dog were in the room before the husband entered. The dog would willingly go for walks with the husband, but only the wife could be in the kitchen when the dog was eating. The dog was most likely to attack the man when he tried to enter his bedroom if the wife was already there.
It is impossible to say for sure if such problems are getting worse, though there is no doubt that aggression in dogs is a widespread phenomenon. In Baltimore, a city of 80,000 to 100,000 dogs, there were 7,000 attacks on people in one year, according to a classic 1973 study. According to the Centers for Disease Control and Prevention, each year in the United States 800,000 people are injured seriously enough by dogs to require medical attention, 6,000 are hospitalized by dog attacks, and about fifteen, mostly children, are killed.
And of course some dog behavioral problems are owner problems. Because dogs are so good at picking up on social signals, our psychological failings readily affect the way our pets act. A survey of cocker-spaniel owners in Britain found that less-assertive owners had more-aggressive dogs. There has been a distinct upsurge in the "yuppie-puppy syndrome," as young working couples buy dogs and leave them alone at home all day to ruin the house—and then spoil them out of guilt for neglecting them. There is also a marked tendency, noted by dog breeders and veterinarians alike, for expectations and realities to clash, because members of an increasingly urban society do not always know what they are getting themselves into when they bring a high-energy herding or hunting dog into their lives.
But there are several reasons to think that canine aggression and other behavioral problems as they exist today are not a "normal" part of the evolved relationship. Nor are they merely the result of individual owners' personality traits. Over the course of 100,000 years there should have been a considerable amount of selection (even if it was largely unwitting) against aggressive dogs. And most people who seek help for behavioral problems with their dogs, Houpt says, have "done all the right things." Feral dogs, significantly, are not very aggressive. Studies of urban dogs found that strays were only a third as likely as owned dogs to exhibit aggression toward people when approached. Most wolves are not really aggressive either. There is only one "alpha," or dominant, male in a pack. Most wolves, and most dogs, are not alpha in the natural scheme of things.
Many people explain the persistence of canine aggression by pointing to deliberate efforts within certain human subcultures to breed aggressive dogs as status symbols or for protection. But even this cannot completely explain what is going on. Notoriously aggressive breeds like Dobermans and German shepherds do show up on lists of problem dogs; but according to Houpt's research, so do springer spaniels and cocker spaniels—and aggression among these, which hardly rank as notoriously aggressive breeds, may be a phenomenon of the past several decades. Among owners of springer spaniels the phenomenon is widely recognized; they call it "springer rage," only slightly tongue-in-cheek. According to a survey by Houpt, 27 percent of springer spaniels had bitten a person—at least twice the average rate for dogs.
Such streaks of aggression may seem odd, and they are odd. They seem to be traceable quite directly to the way dogs have been bred for the past century. By now nearly everyone has heard about the evils of inbreeding in dogs, and hip dysplasia and other hereditary diseases are forever being cited by animal-rights activists in their campaigns against pet ownership in general and dog breeders in particular. Such defects are often presented as the inevitable consequence of any attempt by humankind to manipulate or direct the evolution of a species toward characteristics it happens to fancy.
But genetic markers imply that up until a century or so ago people did successfully develop many highly distinctive varieties of dogs—everything from lap dogs to attack dogs, bird dogs to sled dogs—without a loss of overall genetic diversity, and without a rise in physical or behavioral abnormalities. The evidence also suggests that the problems that have arisen are less a direct consequence of deliberate breeding practice—as is usually alleged—than a largely avoidable side effect of it.
Historically, dogs were mostly categorized by general type. There were sheep dogs, foxhounds, spaniels, pointers, retrievers. But pointers were just pointers—they weren't German short-haired pointers or Vizslas or Weimaraners. As Wayne's genetic data show, interbreeding and a flow of genes on a worldwide scale was continuing even as this segregation into types was taking place. The types were distinct in both physical appearance and behavior; they clearly had been selected with specific human aims in mind. But the crucial point is that these dogs were defined by form and function rather than by parentage. They were what livestock breeders would today call "open" or "grade" breeds.
Beginning around 1870, however, with the establishment of kennel clubs in Britain and the United States, closed breeding books were introduced in the name of developing and maintaining "purebred" animals. A dog could be registered as a Vizsla only if both of its parents were registered as Vizslas. There was more than a little racist thinking behind all of this; writings about animal breeding from the late 1800s and early 1900s are full of exhortations to eliminate "weaklings" and to invigorate the race by maintaining the "purity" of its "blood lines." Look up any bibliography of dog books and the name Leon Fradley Whitney is sure to appear. Whitney was the author of many standard works, including The Complete Book of Dog Care (still in print), This Is the Cocker Spaniel, Bloodhounds and How to Train Them, and How to Breed Dogs.What you won't find in a dog bibliography is some other Whitney works, including The Case for Sterilization, a paean to eugenics published in 1934. It was such a definitive treatment that the author received a letter of appreciation from no less an authority on the subject than Adolf Hitler. (Whitney in turn publicly hailed Hitler's "great statesmanship" in ordering the sterilization of the feeble-minded and the insane. In an unpublished autobiography written four decades later Whitney still defended his stance, maintaining that "no ruler ever before had had the courage or the knowledge to put sterilization to work." He allowed, however, that in the 1930s he had not been aware "what a vile human being" Hitler was.)
Today, when an unscientific embrace of "biodiversity" is almost as common as the unscientific embrace of "racial purity" was a century ago, inbreeding is often portrayed as an unmitigated evil. But that is almost as much an oversimplification as the uncritical embrace of purity for purity's sake was. Inbreeding has in fact been a vital technique in the development of virtually every strain of plant and animal useful to agriculture, and it is the only way to rapidly develop a line that will consistently produce certain desirable characteristics. This is at heart a consequence of the biological fact that chromosomes come in pairs; one is inherited from each parent. Closely related individuals—brothers and sisters, parents and offspring—are more likely to carry the same genes. So a mating between two closely related individuals increases the likelihood that the offspring will wind up with the same gene for a given trait on both chromosomes—a state called homozygosity. An organism that is heterozygous for a given trait—that is, has different versions of the gene on each chromosome—may look the same as one that is homozygous, but it will not pass that trait to its offspring as consistently. In the classic human example, both a homozygous individual and a heterozygous one can have brown eyes, though the latter has one gene for brown eyes and one for blue eyes. Brown is "dominant" in this case. But the "recessive" (blue) genes carried by two heterozygous individuals may combine in reproduction to produce offspring who are homozygous for the recessive trait and who will thus be different in appearance—a person with two blue genes has blue eyes. With a homozygous mating, though, what you see is what you get. No matter which of each parent's pair of chromosomes gets passed on to the offspring, the result is the same. In other words, homozygotes breed "true to type" for the traits they have been selected for.
But since closely related individuals have a lot of other genes in common too, inbreeding also increases the chances that any genes for undesirable recessive traits carried at other sites on the genome will combine to produce trouble. Inbred faults in domestic animals tend to be recessive because genetic diseases caused by dominant traits are quickly weeded out in a breeding program: eliminate from the breeding population all the animals that manifest such a disease, and you eliminate the genes for that disease from the entire breeding population. (It takes but a single dominant gene to cause a dominant disease, so there are no "silent" carriers of such genes.) But genetic diseases that show up only in an animal homozygous for a recessive trait can be carried silently for generations. Only when two carriers happen to mate will the disease appear.
Genetic data confirm that the past century of dog breeding has produced some extremely inbred animals. Surveys using gene markers show that the chance that two members of a typical human family will have a different combination of genes at a given site is about 71 percent. In crossbred dogs it is 57 percent, in most purebred dogs 22 percent, and in some rare breeds four percent. Even crossbred dogs are more inbred than the most inbred human populations (the Amish, for example, or families in India in which uncle-niece marriages take place).
This degree of uniformity means that when a bad trait does get locked in by chance, it tends to stay as long as breeding is confined within the group. And a raft of genetic diseases have been turning up in a variety of dog breeds. Some of them are truly bizarre: epilepsy in poodles, sudden muscle rigidity in Scottish terriers ("Scottie cramp"), chronic fever in Shar-Peis, tumors in flat-coated retrievers, congestive heart failure in boxers.
The dog-show world—the American Kennel Club in particular—is often blamed for having created these genetic diseases through an obsessive preoccupation with physical appearance in breed definitions. But that criticism misses most of the point. Selecting for one thing (such as looks) doesn't mean you can't also select for other things (such as herding behavior and good health) at the same time. Breeders can narrowly select for traits that suit their fancy and still not unlock recessive diseases or lose desirable behaviors—if they start from a large founding population and make sure that they keep a broad representation of the founders' gene pool in all subsequent generations. Working foxhounds are intensely scrutinized for body conformation at competitions; they are also meticulously selected for their ability to follow a fox's trail and to work together as a pack, and their readiness to speak when they find scent. Border collies are selected for herding ability; they almost all happen to have white collars and white tips on their tails as well.
The real source of genetic trouble in many breeds is not so much that dogs are being bred for looks or to meet other narrow criteria as that the breed has relatively few founders. Many breeds suffer from the "popular sire effect" as well, and here criticism of the breeding world is more justifiable. A stud dog that wins a blue ribbon at a major show may father hundreds of litters, swamping the gene pool with his virtues—and defects—and crowding out some other ancestral lines altogether. The problem is worse in breeds that have gone through a genetic bottleneck. A number of breeds that exhibit strange recessive ailments, including Irish wolfhounds, flat-coated retrievers, Portuguese water dogs, and Shar-Peis, almost disappeared at some point during this century and were reconstituted from very small populations.
Streaks of aggressiveness in a breed like the springer spaniel could likewise be the result of recessive traits being inadvertently locked in to a closed population with a relatively small founder base. But selection may play a role too, and this is another instance in which the show ring may be to blame. Dogs that carry their heads and tails erect catch the attention of judges, and thus tend to win shows. Those are also the marks of a dominant, hence aggressive, dog. Some show-dog breeders don't actually live with their dogs (the dogs stay in kennels), and so are willing to put up with bad traits in a single-minded pursuit of the perfect coat or the half-pricked ear.
One strikingly counterintuitive conclusion of modern genetic studies is that the worst way to correct these mistakes of the past is to weed the carriers of genetic diseases out of the breeding population. The central fallacy of the racist view of eugenics was embodied in the claim that purity is genetically invigorating. In fact just the opposite is true—genetic diversity is invigorating (thus "hybrid vigor," well known to agricultural breeders), because it helps to ensure that breeding for homozygosity in desirable traits doesn't at the same time breed for homozygosity in undesirable traits at other sites on the genome. Even disease carriers have a valuable contribution to make in preserving heterozygosity: a dog that carries an epilepsy gene, for example, could also very well carry a gene that protects against cancer. That is a point that Deborah Lynch, of the AKC Canine Health Foundation (which spends about $1 million annually on academic research into canine diseases, about half of that in genetics), emphasizes.
The key is not to cull the carriers (that is, animals that possess just one defective gene and so don't exhibit the ailment) but, rather, never to breed two carriers. "The first thing a novice breeder will do is say, 'Oh, my gosh, there's a problem in my line, I'm going to get rid of everything and start over,'" Lynch says. "Well, all you're doing with that is starting over with someone else's problems." The solution is to keep parentage as diverse as possible while correcting the problem—and correcting it will become easier and easier as more genetic probes for specific canine ailments are developed.
Clearly, dog breeders are becoming far more sophisticated in their understanding of genetics and more forthright in facing up to inbred problems that just a few years ago they tended to disregard. But old habits die hard, and amid the eclat of new genetic research one can occasionally make out strains of Leon F. Whitney's old tune. A number of breeders are seeking genetic probes not to detect disease but rather to measure "genetic purity"—to test, for example, if a Vizsla really is a Vizsla, or if (horrors) tainted blood has crept in. But breeding for the purity of the breed is like hiring a storyteller not on the basis of how well he tells stories but after looking at how many generations of Irishmen he has in his background. The fact is that any genetic markers that happen to be associated with a given breed are just a matter of chance. Yes, it is possible, owing to the high degree of inbreeding in dogs, to find some (usually junk) DNA that is unique to one breed. But that is a matter of genetic chance, not genetic necessity, and a breeder who set out to foil the system could easily do so. A dog might be bred deliberately to pass the Vizsla genetic-purity test while looking like a cross between a Pekingese and a coyote. A more sensible strategy would be to breed dogs for chosen characteristics and for the maintenance of genetic diversity. From a scientific point of view, it is perfectly possible to do this while satisfying the desires of dog breeders to maintain distinctive breeds. Zoo keepers go to great lengths to ensure that subsequent generations of the rare species in their care—considered as a worldwide population—will reflect the total range of existing genetic diversity within the species. Zoos are continually swapping breeding animals or frozen semen.
Individual dog breeders do not have the same incentive to act in concert; the short-term rewards still go to those who can offer puppies that were sired by a champion dog. In the long run, however, the increased availability of genetic tests will make it obvious which breeders have sacrificed good genes in their quest for puppies with flashy pedigrees. Already there are genetic probes available to detect carriers of cystinuria in Newfoundland dogs; Von Willebrand's disease, a bleeding disorder, in poodles and Manchester terriers; and copper toxicosis in Bedlington terriers. Many breed clubs are requiring, or providing strong incentives for, the use of such tests as they become available.
The sheer diversity of dog breeds, and the fact that up until a hundred years ago—a blink of an eye in terms of evolutionary time scales—genes flowed freely throughout the global dog population, together imply that we still have ample genetic reserves that can be drawn on to undo any damage recently done. Taken as a whole, the genetic diversity of the dog remains as great as that of its wild ancestors.
We can take some reassurance, too, from the fact that mutts, owned and unowned, will always be with us. Despite the efforts of neo-eugenicists to ostracize them, mutts constitute a vibrant reservoir of canine genetic diversity. Mutts tend to be healthy dogs, because of hybrid vigor. They also tend to be good dogs. And in a very real sense mutts today embody the evolutionary heritage of the True Dog—that animal that evolved with us, that adapted to and exploited our society, and did so largely on his own terms. Defiant of human fashion and whim, selected only in accordance with the ancient evolutionary dictate that demands nothing more than an ability to get along with rather gullible human beings, mutts are really what dogs are about. If worst comes to worst, perhaps they will set us straight, just as their ancestors so ably did—at least for 99,900 of the past 100,000 years.