To understand what the dog is about we have to understand from where he came. As a member of the Canidae Canidae family-all of whose members are called family-all of whose members are called canids canids-the domestic dog is distantly related to coyotes and jackals, dingoes and dholes, foxes and wild dogs.*

But he arose from just one ancient Canidae Canidae line, animals most likely resembling the contemporary gray wolf. When I see Pumpernickel delicately spit out a raisin, though, I am not reminded of the stark images of wolves in Wyoming downing a moose and yanking it apart. The existence of an animal who will patiently wait at the kitchen door, and then ponderously consider a carrot stick, seems at first glance irreconcilable with that of an animal whose primary allegiance is to himself, whose affiliations are fraught with tension and maintained by force. line, animals most likely resembling the contemporary gray wolf. When I see Pumpernickel delicately spit out a raisin, though, I am not reminded of the stark images of wolves in Wyoming downing a moose and yanking it apart. The existence of an animal who will patiently wait at the kitchen door, and then ponderously consider a carrot stick, seems at first glance irreconcilable with that of an animal whose primary allegiance is to himself, whose affiliations are fraught with tension and maintained by force.

Carrot-considerers arose out of moose killers through the second source: us. Where nature blindly, uncaringly "selects" traits that lead to the survival of their bearers, ancestral humans have also selected traits-physical features and behaviors-that have led not just to the survival, but to the omnipresence of the modern dog, Canis familiaris, Canis familiaris, among us. The animal's appearance, behavior, preferences; his interest in us and attention to our attention: these are largely the result of domestication. Present-day dog is a well-designed creature. Only much of this design was utterly unintentional. among us. The animal's appearance, behavior, preferences; his interest in us and attention to our attention: these are largely the result of domestication. Present-day dog is a well-designed creature. Only much of this design was utterly unintentional.

HOW TO MAKE A DOG: STEP-BY-STEP INSTRUCTIONS.

So you want to make a dog? There are just a few ingredients. You'll need wolves, humans, a little interaction, mutual tolerance. Mix thoroughly and wait, oh, a few thousand years.

Or, if you're the Russian geneticist Dmitry Belyaev, you simply find a group of captive foxes and start selectively breeding them. In 1959, Belyaev began a project that has greatly informed our best guesses as to what we believe the earliest steps of domestication were. Instead of observing dogs and extrapolating backward, he examined another social canid species and propagated them forward. The silver fox in Siberia in the mid-twentieth century was a small, wild animal that had become popular with the fur trade. Kept in pens, bred for their choice fur coats, particularly long and soft, the fox was not tamed but was captive. What Belyaev made of them, with a much reduced recipe, were not "dogs," but were surprisingly close to dogs.

Though Vulpes vulpes, Vulpes vulpes, the silver fox, is distantly related to wolves and dogs, it had never before been domesticated. Despite their evolutionary relatedness, no canids are fully domesticated other than the dog: domestication doesn't happen spontaneously. What Belyaev showed was that it can happen quickly. Beginning with 130 foxes, he selectively chose and bred those that were the most "tame," as he described it. What he really chose were those foxes that were the least fearful of or aggressive toward people. The foxes were caged, so aggression was minimal. Belyaev approached each cage and invited the fox to eat some food out of his hand. the silver fox, is distantly related to wolves and dogs, it had never before been domesticated. Despite their evolutionary relatedness, no canids are fully domesticated other than the dog: domestication doesn't happen spontaneously. What Belyaev showed was that it can happen quickly. Beginning with 130 foxes, he selectively chose and bred those that were the most "tame," as he described it. What he really chose were those foxes that were the least fearful of or aggressive toward people. The foxes were caged, so aggression was minimal. Belyaev approached each cage and invited the fox to eat some food out of his hand.

Some bit at him; some hid. Some took the food, reluctantly. Others took the food and also let themselves be touched and patted without fleeing or snarling. Still others accepted the food and even wagged and whimpered at the experimenter, inviting rather than discouraging interaction. These were the foxes Belyaev selected. By some normal variation in their genetic code, these animals were naturally calmer around people, even interested in people. None of them had been trained; all had the same, minimal exposure to human caretakers, who fed them and cleaned their bedding for their short lives.

These "tame" foxes were allowed to mate, and their young were tested the same way. The tamest of those were mated, when they were old enough; and their young; and their young. Belyaev continued the work until his death, and the program has continued since. After forty years, three-quarters of the population of foxes were of a cla.s.s the researchers called "domesticated elite": not just accepting contact with people, but drawn to it, "whimpering to attract attention and sniffing and licking"... as dogs do. He had created a domesticated fox.

Later genomic mapping has revealed that forty genes now differ between Belyaev's tame foxes and the wild silver fox. Incredibly, by selecting for one behavioral trait, the genome of the animal was changed in a half century. And with that genetic change came a number of surprisingly familiar physical changes: some of the later-generation foxes have multicolored, piebald coats, recognizable in dog mutts everywhere. They have floppy ears and tails that curl up and over their backs. Their heads are wider and their snouts are shorter. They are improbably cute.

All these physical characteristics came along for the ride, once a particular behavior was chosen and picked out. The behavior is not what affects the body; instead, both are the common result of a gene or set of genes. Single behaviors aren't dictated by genes, but they are made more or less likely by them. If someone's genetic makeup leads to having very high levels of a stress hormone, for instance, it doesn't mean that they will be stressed all the time. But it may mean that they have a lowered threshold for having the cla.s.sic stress response-a raised heart rate and breathing rate, increased sweating, and so on-in some contexts where someone else doesn't have a stress response. Let's say this low-threshold character screams at her dog for barreling into her at the dog park. Her screaming at the poor pup certainly is not genetically obliged-genes don't know from dog parks, or even pups-but her neurochemistry, created from her genes, facilitated it happening when a situation presented itself.

So, too, with the doglike foxes. Given what genes do,* even a small change in a gene-turning on slightly later than it otherwise might, say-could change the likelihood of both certain behaviors and certain forms of physical appearance. Belyaev's foxes show that a few simple developmental differences can have a wide-ranging effect: for instance, his foxes open their eyes earlier and show their first fear responses later, more like dogs than wild foxes. This gives them a longer early window for bonding with a caretaker-such as a human experimenter in Siberia. They play with each other even when they reach adulthood, perhaps allowing for longer and more complex socialization. It is worth noting that foxes diverged from wolves some ten to twelve million years ago; yet in forty years' of selection they look domesticated. The same perhaps could happen with other carnivores we take under our wing and inside our houses. The genetic changes nudge them into being doggy.

HOW WOLVES BECAME DOGS.

Though we tend not to think much about it, the history of dogs, well before you got your dog, bears more on what your dog is like than the particulars of his parentage. Their history begins with wolves.

Wolves are dogs before the accoutrements. The coat of domestication makes dogs quite different creatures, however.* While a pet dog gone missing may not survive even a handful of days on his own, the anatomy, instinctual drive, and sociality of the wolf combine to make it very adaptable. These canids can be found in diverse environments: in deserts, forests, and on ice. For the most part, wolves live in packs, with one mating pair and from four up to forty younger, usually related wolves. The pack works cooperatively, sharing tasks. Older wolves may help raise the youngest pups, and the whole group works together when hunting large prey. They are very territorial and spend a good amount of time demarcating and defending their borders.

Inside some of these borders, tens of thousands of years ago, human beings began to appear. h.o.m.o sapiens, h.o.m.o sapiens, having outgrown his having outgrown his habilis habilis and and erectus erectus forms, was becoming less nomadic and beginning to create settlements. Even before agriculture began, interactions between humans and wolves began. Just how those interactions played out is the source of speculation. One idea is that the humans' relatively fixed communities produced a large amount of waste, including food waste. Wolves, who will scavenge as well as hunt, would have quickly discovered this food source. The most brazen among them may have overcome any fear of these new, naked human animals and begun feasting on the sc.r.a.ps pile. In this way, an accidental natural selection of wolves who are less fearful of humans would have begun. forms, was becoming less nomadic and beginning to create settlements. Even before agriculture began, interactions between humans and wolves began. Just how those interactions played out is the source of speculation. One idea is that the humans' relatively fixed communities produced a large amount of waste, including food waste. Wolves, who will scavenge as well as hunt, would have quickly discovered this food source. The most brazen among them may have overcome any fear of these new, naked human animals and begun feasting on the sc.r.a.ps pile. In this way, an accidental natural selection of wolves who are less fearful of humans would have begun.

Over time, humans would tolerate the wolves, maybe taking a few pups in as pets, or, in leaner times, as meat. Generation by generation, the calmer wolves would have more success living on the edge of human society. Eventually, people would begin intentionally breeding those animals they particularly liked. This is the first step of domestication, a remaking of animals to our liking. With all species, this process typically occurs through a gradual a.s.sociation with humans, whereby successive generations become more and more tame and finally become distinct in behavior and body from their wild ancestors. Domestication is thus preceded by a kind of inadvertent selection of animals who are nearby, useful, or pleasing, allowing them to loiter on the edges of human society. The next step in the process involves more intention. Those animals who are less useful or liked are abandoned, destroyed, or deterred from hanging about with us. In this way, we select those animals who more easily submit to our breeding of them. Finally, and most familiar, domestication involves breeding animals for specific characteristics.

Archeological evidence dates the first domesticated wolf-c.u.m-dog at ten thousand to fourteen thousand years ago. Dog remains have been found in trash heaps (suggesting their use as food or property) and in grave sites, their skeletons curled up aside human skeletons. Most researchers think dogs began to a.s.sociate with us even earlier, maybe many tens of thousands of years ago. There is genetic evidence, in the form of mitochondrial DNA samples,* of a subtle split as long as 145,000 years ago between pure wolves and those that were to become dogs. We could call the latter wolves protodomesticators, since they had themselves changed behaviorally in ways that would later encourage humans' interest (or merely tolerance) of them. By the time humans came along, they might have been ripe for domesticating. The wolves taken up by humans were probably less hunters than scavengers, less dominant and smaller than alpha wolves, and tamer. In sum, less wolfy. Thus, early in the development of ancient civilizations, thousands of years before domesticating any other animal, humans took this one animal with them inside the walls of their fledgling villages.

These vanguard dogs would not be mistaken as members of one of the hundreds of currently recognized dog breeds. The short stature of the dachshund, the flattened nose of the pug-these are the results of selective breeding by humans much later. Most dog breeds we recognize today have only been developed in the last few hundred years. But these early dogs would have inherited the social skills and curiosity of their wolf ancestors, and would then have applied them toward cooperating with and appeasing humans as much as toward each other. They lost some of their tendency toward pack behavior: scavengers don't need the proclivity to hunt together. Nor is any hierarchy relevant when you might live and eat on your own. They were sociable but not in a social hierarchy.

The change from wolf to dog was striking in its speed. Humans took nearly two million years to morph from h.o.m.o habilis h.o.m.o habilis to to h.o.m.o sapiens, h.o.m.o sapiens, but the wolf leapfrogged into dogness in a fraction of the time. Domestication mirrors what nature, through natural selection, does over hundreds of generations: a kind of artificial selection that hurries up the clock. Dogs were the first domesticated animals, and in some ways the most surprising. Most domestic animals are not predators. A predator seems like an unwise choice to take into one's home: not only would it be difficult to find provisions for a meat eater, one risks being seen as meat oneself. And though this might make them (and has made them) good hunting pals, their main role in the last hundred years has been to be a friend and nonjudgmental confidant, not a worker. but the wolf leapfrogged into dogness in a fraction of the time. Domestication mirrors what nature, through natural selection, does over hundreds of generations: a kind of artificial selection that hurries up the clock. Dogs were the first domesticated animals, and in some ways the most surprising. Most domestic animals are not predators. A predator seems like an unwise choice to take into one's home: not only would it be difficult to find provisions for a meat eater, one risks being seen as meat oneself. And though this might make them (and has made them) good hunting pals, their main role in the last hundred years has been to be a friend and nonjudgmental confidant, not a worker.

But wolves do have features that made them terrific candidates for artificial selection. The process favors a social animal who is behaviorally flexible, able to adjust its behavior in different settings. Wolves are born into a pack, but only stay until they are a few years old: then they leave and find a mate, create a new pack, or join an already existing pack. This kind of flexibility to changing status and roles is well suited to dealing with the new social unit that includes humans. Within a pack or moving between packs, wolves would need to be attentive to the behavior of packmates-just as dogs will need to be attentive to their keepers and sensitive to their behavior. Those early wolf-dogs meeting early human settlers would not have benefited the humans much, so they must have been valued for some other reason-say, for their companionship. The openness of these canids allowed them to adjust to a new pack: one that would include animals of an entirely different species.

UNWOLFY.

And so some wolflike ancestor of both wolves and dogs took the plunge, loitered among human loiterers, and was eventually adopted and then molded by humans instead of solely by the caprice of nature. This makes present-day wolves an interesting comparison species to dogs: they likely share many traits. The present-day wolf is not the ancestor of the dog; though wolves and dogs share a common ancestor. Even the modern wolf is likely quite different than the ancestral wolves. What is different between dogs and wolves is probably due to what made some protodogs likely to be taken in, plus whatever humans have done in breeding them since.

And there are many differences. Some are developmental: for instance, dogs' eyes don't open for two or more weeks, whereas wolf pups open their eyes at ten days old. This slight difference can have a cascading effect. Generally, dogs are slower to develop physically and behaviorally. The big developmental milestones-walking, carrying objects in the mouth, when they first engage in biting games-come generally later for dogs than for wolves.* This small difference blossoms into a large difference: it means that the window for socialization is different in dogs and wolves. Dogs have more leisure to learn about others and to become accustomed to objects in their environment. If dogs are exposed to non-dogs-humans or monkeys or rabbits or cats-in the first few months of development, they form an attachment to and preference for these species over others, often trumping any predatory or fearful drive we might expect them to feel. This so-called sensitive sensitive or or critical critical period of social learning is the time during which dogs will learn who is a dog, an ally, or a stranger. They are most susceptible to learning who their peers are, how to behave, and a.s.sociations between events. Wolves have a smaller window during which to determine who is familiar and who is foe. period of social learning is the time during which dogs will learn who is a dog, an ally, or a stranger. They are most susceptible to learning who their peers are, how to behave, and a.s.sociations between events. Wolves have a smaller window during which to determine who is familiar and who is foe.

There are differences in social organization: dogs do not form true packs; rather, they scavenge or hunt small prey individually or in parallel.* Though they don't hunt cooperatively, they are cooperative: bird dogs and a.s.sistance dogs, for instance, learn to act in synchrony with their owners. For dogs, socialization among humans is natural; not so for wolves, who learn to avoid humans naturally. The dog is a member of a human social group; its natural environment, among people and other dogs. Dogs show what is called with human infants "attachment": preference for the primary caregiver over others. They have anxiety at separation from the caregiver, and greet her specially on her return. Though wolves greet other members of the pack when they reunite after being apart, they don't seem to show attachment to particular figures. For an animal who is going to be around humans, specific attachments make sense; for an animal who lives in a pack, it is less applicable.

Physically, dogs and wolves differ. While still quadrupedal omnivores, the range of body types and sizes among dogs is extraordinary. No other canid, or other species, shows the same diversity of body types within a species, from the four-pound papillon to the two-hundred-pound Newfoundland; from slender dogs with long snouts and whiplike tails to pudgy dogs with foreshortened noses and stubs of tails. Limbs, ears, eyes, nose, tail, fur, haunches, and belly are all dimensions along which dogs can be reconfigured and still be dogs. Wolves' sizes, by contrast, are, like most wild animals, fairly reliably uniform in a particular environment. But even the "average" dog-something resembling a prototypical mutt-is distinguishable from the wolf. The dog's skin is thicker than wolves'; while both have the same number and kind of teeth, the dog's are smaller. And the whole head is smaller on a dog than on a wolf: about 20 percent smaller. In other words, between a dog and a wolf of similar body size, the dog has the much smaller skull-and, correspondingly, a smaller brain.

This latter fact has continued to be promulgated, perhaps an indication of the ongoing appeal of the claim (now debunked) that brain size determines intellect. While erroneous, the smoothness of the shift from talking about brain size size to brain to brain quality quality trumped evidence to the contrary. Comparative studies with wolves and dogs on problem-solving tasks initially seemed to confirm dogs' cognitive inferiority. Hand-raised wolves tested on their ability to learn a task-to pull three ropes from an array of ropes in a particular order-well outperformed the dogs tested. The wolves more quickly learned to pull any rope to begin and then proceeded to be more successful at learning the order in which the ropes were to be pulled. (They also tore more ropes to pieces than the dogs did, although the researchers are silent about what this indicates about their cognition.) Wolves are also great at escaping from enclosed cages; dogs are not. Most canid researchers agree that wolves pay more attention than dogs do to physical objects and handle these objects more capably. trumped evidence to the contrary. Comparative studies with wolves and dogs on problem-solving tasks initially seemed to confirm dogs' cognitive inferiority. Hand-raised wolves tested on their ability to learn a task-to pull three ropes from an array of ropes in a particular order-well outperformed the dogs tested. The wolves more quickly learned to pull any rope to begin and then proceeded to be more successful at learning the order in which the ropes were to be pulled. (They also tore more ropes to pieces than the dogs did, although the researchers are silent about what this indicates about their cognition.) Wolves are also great at escaping from enclosed cages; dogs are not. Most canid researchers agree that wolves pay more attention than dogs do to physical objects and handle these objects more capably.

From results like these comes the notion that there is a cognitive difference between wolves and dogs: usually, that wolves are insightful problem solvers, and dogs simpletons. In actual fact, historically theories have oscillated between claiming dogs to be more intelligent, or wolves to be the smarter of the two. Science is often contingent on the culture in which it is practiced, and these theories reflect the then-prevailing ideas about animal minds. The acc.u.mulated data of dog and wolf behavior, though, leads to a more nuanced position. Wolves seem to be better at solving certain kinds of physical physical puzzles. Some of this skill is explainable by looking at their natural behavior. Why did wolves readily learn the rope-pulling task? Well, they do a lot of grabbing and pulling on things (like prey) in their natural environment. Some of the difference can be traced to dogs' more limited requirements for living. Having been folded into the world of humans, dogs no longer need some of the skills that they would to survive on their own. As we'll see, what dogs lack in physical skills, they make up for in people skills. puzzles. Some of this skill is explainable by looking at their natural behavior. Why did wolves readily learn the rope-pulling task? Well, they do a lot of grabbing and pulling on things (like prey) in their natural environment. Some of the difference can be traced to dogs' more limited requirements for living. Having been folded into the world of humans, dogs no longer need some of the skills that they would to survive on their own. As we'll see, what dogs lack in physical skills, they make up for in people skills.

AND THEN OUR EYES MET ...

There is a final, seemingly minor difference between the two species. This one small behavioral variation between wolves and dogs has remarkable consequences. The difference is this: dogs look at our eyes.

Dogs make eye contact and look to us for information-about the location of food, about our emotions, about what is happening. Wolves avoid eye contact. In both species, eye contact can be a threat: to stare is to a.s.sert authority. So too is it with humans. In one of my undergraduate psychology cla.s.ses, I have my students do a simple field experiment wherein they try to make and hold eye contact with everyone they pa.s.s on campus.

Both they and those on the receiving end of their stares behave remarkably consistently: everyone can't wait to break eye contact. It's stressful for the students, a great number of whom suddenly claim to be shy: they report that their hearts begin to race and they start sweating when simply holding someone's gaze for a few seconds. They concoct elaborate stories on the spot to explain why someone looked away, or held their gaze for a half second longer. For the most part, their staring is met with deflected gazes from those they eyeball. In a related experiment, they test gaze in a second way, verifying our species' tendency to follow the gaze of others to its focal point. A student approaches any publicly visible and shared object-a building, tree, spot on the sidewalk-and looks fixedly at one point on it. Her partner, another student, stands nearby and surrept.i.tiously records the reactions of pa.s.sersby. If it's not rush hour and raining, they report finding that at least some people stop in their tracks to follow their gaze and stare curiously at that fascinating sidewalk spot: surely there must be something. something.

If this behavior is unsurprising, it is because it is so human: we look. Dogs look, too. Though they have inherited some aversion to staring too long at eyes, dogs seem to be predisposed to inspect our faces for information, for rea.s.surance, for guidance. Not only is this pleasing to us-there is a certain satisfaction in gazing deep into a dog's eyes gazing back at you-it is also perfectly suited to getting along with humans. As we will see later in this book, it also serves as a foundation for their skill at social cognition. We not only avoid eye contact with strangers, we rely on eye contact with intimates. There is information in a furtive glance; a gaze mutually held feels profound. Eye contact between people is essential to normal communication.

Hence a dog's ability to find and gaze at our eyes may have been one of the first steps in the domestication of dogs: we chose those that looked at us. What we then did with dogs is peculiar. We began designing them.

FANCY DOGS.

The label on her cage said "Lab mix." Every dog in the shelter was a Lab mix. But surely Pump was born of a spaniel: her black, silky hair fell against her slender frame; her velvet ears framed her face. In sleep she was a perfect bear cub. Soon her tail hairs grew longer and feathery: so she's a golden retriever. Then the gentle curls on her underbelly tightened; her jowls filled a bit: okay, she's a water dog. As she ages her belly grows until she has a solid, barrel-like shape-she's a Lab after all; her tail becomes a flag needing tr.i.m.m.i.n.g-a Lab/golden mix; she could be still one moment and sprinting the next-a poodle. She is curly and round-bellied: clearly the product of a sheepdog who'd snuck into the bushes with a pretty sheep. She's her own dog.

The original dogs were mongrels, in the sense that they didn't come from a controlled lineage. But many of the dogs we keep, mutts or not, emerged from hundreds of years of strictly controlled breeding. The consequence of this breeding is the creation of what are nearly subspecies, varying in shape, size, lifetime, temperament,* and skills. The outgoing Norwich terrier, ten inches high and ten pounds strong, is but the weight of the calm, sweet, enormous Newfoundland's head. Ask some dogs to retrieve a ball and you get a puzzled look; but a border collie doesn't need to be asked twice.

The familiar differences between modern breeds aren't always the result of intentional selection. Some behaviors and physical features are selected for-retrieving prey, smallness, a tightly curled tail-and some just come along for the ride. The biological reality of breeding is that the genes for traits and behaviors come in cl.u.s.ters. Mate a few generations of dogs with particularly long ears and you might find that they all share other characteristics: a strong neck, downcast eyes, fine jowls. Coursing dogs, bred to gallop swiftly or long, are leggy-their leg length matches (in the husky) or surpa.s.ses (in the greyhound) the depth of their chests. By contrast, dogs who track on the ground (as the dachshund) wound up with legs much shorter than their chest is deep. Similarly, selecting for one particular behavior inadvertently selects for accompanying behaviors. Breed dogs who are very sensitive to motion-who probably have an overabundance of rod photoreceptors in their retinae-and you may also get a dog whose acute sensitivity to motion leads to their being temperamentally high-strung. Their appearance might change, too: they may have large, globular eyes for seeing at night. Sometimes what comes to be desirable in a breed is a trait that first appeared inadvertently.

There is evidence of distinct dog breeds as early as five thousand years ago. In drawings from ancient Egypt, at least two kinds of dogs are depicted: mastiff-looking dogs, big of head and body, and slim dogs with curled tails.* The mastiffs may have been guard dogs; the slender dogs appear to have been hunting companions. And so the designing of dogs for particular purposes began-and continued along these lines for a long while. By the sixteenth century, there were added other hounds, bird dogs, terriers, and shepherds. By the nineteenth century, clubs and compet.i.tions sprouted, and the naming and monitoring of breeds exploded.

The various modern breeds have probably all emerged with this proliferation of breeding in the last four hundred years. The American Kennel Club now lists nearly one hundred fifty varieties, grouped according to the purported* occupation of the breed. Hunting companions are distributed into "sporting," "hound," "working," and "terrier" categories; there are, in addition, the working "herding" breeds, the plainly "nonsporting" breeds, and the rather self-explanatory "toys." Even among dogs bred to join the hunt, there are subdivisions, by the very kind of a.s.sistance they provide (pointers point out the prey; retrievers retrieve it; Afghan hounds exhaust it); by the specific prey they're after (terriers are ratters, and harriers go after hares); and by the medium preferred (beagles chase on land; spaniels will swim in water). Worldwide, there are hundreds more breeds still. Breeds vary not just by our uses of them but physically: by body size, head size, head shape, body shape, type of tail, coat kind, coat color. Go searching for a purebred dog and you'll confront a new-car-worthy list of specs, detailing everything from the ears to the temperament of your future pup. Want a long-limbed, short-haired, jowly dog? Consider the Great Dane. In more of a short-nosed, rolled-skin, curly-tailed kind of mood? Here's a nice pug for you. Choosing between breeds is like choosing between anthropomorphized option packages. You not only get a dog, you get one who is typically "dignified, lordly, scowling, sober and sn.o.bbish" (shar-pei); "merry and affectionate" (English c.o.c.ker spaniel); "reserved and discerning with strangers" (chow chow); with a "rollicking personality" (Irish setter); full of "self-importance" (Pekingese); having "heedless, reckless pluck" (Irish terrier); "equable" (Bouvier des Flandres); or, most surprisingly, "a dog at heart" (briard).

The dog fanciers will be surprised to hear, perhaps, that the grouping of breeds based on genetic similarity does not result in the same groupings as the AKC. Cairn terriers are closer to hounds; shepherds and mastiffs share much of their genomes. The genome belies most people's a.s.sumptions about dogs' similarities to wolves, too: the long-haired, sickle-tailed huskies are closer to wolves than the long-bodied, skulking German Shepherd. Basenjis, who bear almost no physical resemblance to wolves, are closer still. This is yet another indication that, for most of their domestication, the dog's appearance was an accidental side effect of his breeding.

Dog breeds are relatively closed genetic populations, meaning that each breed's gene pool is not accepting new genomes from outside the pool. To be a member of a breed, a dog must have parents who are themselves members. Thus any physical changes in the offspring can only come from random genetic mutations, not from the mixing of different gene pools that usually occurs when animals (including humans) mate. Mutations, variation, and admixtures are generally good for populations, though, and help to prevent inherited disease: this is why purebred dogs, though they come from what is considered "good stock" in that the ancestry of the dogs is traceable through the breeding line, are more susceptible to many physical disorders than are mixed-breed dogs.

One boon of a closed gene pool is that the genome of a breed can be mapped, and in fact it recently has: a boxer's genome was the first, around nineteen thousand genes' worth. As a result, scientists are starting to make an accounting of where on the genome the genetic variations are that lead to characteristic traits and disorders, such as narcolepsy, the sudden and total fall into unconsciousness to which some dog breeds (particularly Dobermans) are susceptible.

Another advantage of a closed gene pool of a breed discussed by researchers is that it feels as though one is getting a relatively reliable animal when one selects from it. One can pick a "family-friendly" dog or one advertised as a skillful house guardian. But it is not so simple: dogs, like us, are more than their genome. No animal develops in a vacuum: genes interact with the environment to produce the dog you come to know. The exact formulation is difficult to specify: the genome shapes the dog's neural and physical development, which itself partially determines what will be noticed in the environment-and whatever is noticed itself further shapes continued neural and physical development. As a result, even with inherited genes, dogs aren't just carbon copies of their parents. On top of this, there is also great natural variability in the genome. Even a cloned dog, should you be tempted to replicate your beloved pet, will not be identical to the original: what a dog experiences and whom he meets will influence who he becomes in innumerable, untraceable ways.

So although we have tried to design dogs, the dogs we see today are partly creatures of serendipity. What breed is she? What breed is she? is a question I've been asked about Pump more than any other-and I in turn ask of other dogs. Her mongrelness encourages the great game of guessing her heritage: the resulting hunches are satisfying, even though none could ever be verified.* is a question I've been asked about Pump more than any other-and I in turn ask of other dogs. Her mongrelness encourages the great game of guessing her heritage: the resulting hunches are satisfying, even though none could ever be verified.*

THE ONE DIFFERENCE BETWEEN BREEDS.

Though there is an extensive literature of dog breeds, there has never been a scientific comparison of breed behavior differences: a comparison that controls each animal's environment, giving them the same physical objects, the same exposure to dogs and humans, the same everything. It's hard to believe, given that such bold statements are made about what each breed is like. This is not to suggest that the differences are minimal or nonexistent. Dogs of various breeds will doubtless behave differently when, say, they are presented with a nearby, running rabbit. But it would be a mistake to guarantee that a dog, bred or not, will inevitably act a certain way on seeing that rabbit. This is the same mistake that is made when we wind up calling some breeds "aggressive" and legislating against them.*