Read Inside of a Dog: What Dogs See, Smell, and Know Online

Authors: Alexandra Horowitz

Tags: #General, #Dogs, #Science, #Life Sciences, #Psychology, #Cognitive Psychology, #Dogs - Psychology, #Pets, #Zoology, #Breeds

Inside of a Dog: What Dogs See, Smell, and Know (11 page)

BOOK: Inside of a Dog: What Dogs See, Smell, and Know
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To dogs, we
are
our scent. In some ways, olfactory recognition of people is quite similar to our own visual recognition of people: there are multiple components of the image responsible for how we look. A different haircut or a newly bespectacled face can, at least momentarily, mislead us as to the identity of the person standing before us. I can be surprised what even a close friend looks like from a different vantage or from a distance. So too must the olfactory image we embody be different in different contexts. The mere arrival of my (human) friend at the dog park is enough to set me smiling; it takes another beat before my dog notices her own friend. And odors are subject to decay and dispersal that light is not: a smell from a nearby object may not reach you if a breeze carries it in the other direction, and the strength of an odor diminishes over time. Unless my friend tries ducking behind a tree, it's hard for her to conceal her visual image from me: a wind won't conceal her. But it might conceal her from a dog momentarily.
When we return home at a day's end, dogs typically greet our cocktail of stink promptly and lovingly. Should we come home after having bathed in unfamiliar perfume or wearing someone else's clothes, we might expect a moment of puzzlement—it is no longer "us"—but our natural effusion will soon give us away. Dogs are not alone among animals in seeing in scent. Sharks have been seen to follow the same zigzaggy path through water that an injured fish took some time before: through not just its blood but also its hormones, the fish has left a bit of itself behind. But dogs are unique in being encouraged and trained by people to use scent to follow someone who is visually long gone.
Bloodhounds are one of the supersmellers among dogs. Not only do they have more nose tissue—more
nose
—but many features of their body seem to conspire to enable them to smell extra strongly. Their ears are terrifically long, but not to enable better hearing, as they fall close to the head. Instead a slight swing of the head sets these ears in motion, fanning up more scented air for the nose to catch. Their constant stream of drool is a perfect design to gather extra liquids up to the vomeronasal organ for examination. Basset hounds, thought to be bred from bloodhounds, go one step further: with their foreshortened legs, the whole head is already at ground—scent—level.
These hounds smell well naturally. Through training—rewarding them for attending to certain scents and ignoring others—they are easily able to follow a scent left by someone one or many days before, and can even specify where two individuals parted ways. It doesn't take very much of our odor: some researchers tested dogs using five thoroughly cleaned glass slides, to one of which a single fingerprint was added. The slides were put away for a few hours or up to three weeks. Dogs then got to examine the array of slides, and tried to choose the human slide: they were rewarded with a treat if they guessed correctly, which is sufficient motivation for them to stand and sniff at glass slides. One dog was correct on all but six of one hundred trials. When the slides were then placed outside on the building roof for a week, exposed over the course of the seven days to direct sun, rain, and all manner of blowing debris, the same dog was still correct on almost half the trials—well above chance.
They track not just by noticing odors, but by noticing very small changes in odor. Each of our footsteps will have more or less the same amount of our scent in it. In theory, then, if I saturate the ground with my scent, by running chaotically to and fro, a dog who tracks by noticing that smell won't be able to tell my path—only that I've definitely been there. But trained dogs don't just notice a smell. They notice the change in a smell over time. The concentration of an odor left on the ground by, say, a running footprint, diminishes with every second that passes. In just two seconds, a runner may have made four or five footprints: enough for a trained tracker to tell the direction that he ran based just on the differences in the odor emanating from the first and fifth print. The track you left as you exited the room has more smell in it than the one right before it; thus your path is reconstructed. Scent marks time.

Conveniently, instead of becoming inured to smells over time, as we do, the vomeronasal organ and the dog nose may regularly swap roles, to keep the scent fresh. It is this ability that is exploited when training rescue dogs, who must orient themselves to the odor of someone who has disappeared. Similarly, scenting dogs who trail a criminal suspect are trained to follow what is delicately called our "personal odor generation": our natural, regular, and entirely involuntary butyric acid production. This is easy for them, and they can then extend this skill to smelling other fatty acids, too. Unless you are wearing a body suit made entirely of scentproof plastic, a hound can find you.

You showed fear
Even those of us who are not fleeing a crime scene, or in need of rescue, have a reason not to underestimate just how good a sniffer the dog is. Not only can dogs identify individuals by odor, they can also identify
characteristics
of the individual. A dog knows if you've had sex, smoked a cigarette (done both these things in succession), just had a snack, or just run a mile. This may seem benign: except, perhaps, for the snack, these facts about you might not be of particular interest to a dog. But they can also smell your emotions.
Generations of schoolchildren have been admonished to "never show fear" to a strange dog.* It is likely that dogs do smell fear, as well as anxiety and sadness. Mystical abilities need not be invoked to account for this: fear
smells.
Researchers have identified many social animals, from bees to deer, who can detect pheromones emitted when one animal is alarmed, and who react by taking action to get to safety. Pheromones are produced involuntarily and unconsciously, and through different means: damaged skin may provoke release of them, and there are specialized glands that release chemicals of alarm. In addition, the very feeling of alarm, fear, and every other emotion correlates with physiological changes, from changes in heart rate and breathing rate, to sweating and metabolic changes. Polygraph machines work (to the extent that they work at all) by measuring changes in these autonomic bodily responses; one might say that animals' noses "work" by being sensitive to them as well. Laboratory experiments using rats confirm this: when one rat is given a shock in a cage, and learns to be fearful of the cage, other rats nearby pick up on the shocked rat's fear—even without seeing the rat being shocked—and themselves avoid the cage, which was otherwise not distinguishable from nearby cages.
How does that strange, menacing-looking dog smell our apprehension or fear as he approaches us? We spontaneously sweat under stress, and our perspiration carries a note of our odor on it: that's the first clue to the dog. Adrenaline, used by the body to gear up for a good sprint away from something dangerous, is unscented to us, but not to the sensitive sniffer of the dog: another hint. Even the simple act of increased blood flow brings chemicals more quickly to the surface of the body, where they can be diffused through the skin. Given that we emit odors that reflect these physiological changes accompanying fear, and given the budding evidence of pheromones in humans, chances are that if we've got the heebie-jeebies, a dog can tell. And as we'll see later, dogs are skilled readers of our behavior. We can sometimes see fear in other people in their facial expressions; there is sufficient information in our posture and gait for a dog to see it, too.
In these ways, the fleeing criminal being tracked by dogs is doubly doomed. Dogs can be trained to track based not just on pursuit of a specific person's odor, but also based on a certain kind of odor: the most recent odor of a human in the vicinity (good for finding someone's hiding place), or a human in emotional distress—fearful (as one running from the cops might be), angry, even annoyed.
The smell of disease
If dogs can detect trace amounts of chemicals we leave behind on a doorknob, or in a footprint, might they be able to detect chemicals indicating disease? If you're lucky, when you come down with a disease difficult to diagnose, you'll have a doctor who recognizes, as some have, that a distinctive smell of freshly baked bread about you is due to typhoid fever, or that a stale, sour scent is due to tuberculosis being exhaled from your lungs. According to many doctors, they have come to notice a distinctive smell to various infections, or even to diabetes, cancer, or schizophrenia. These experts come unequipped with the dog's nose—but more equipped to identify disease. Still, a few small-scale experiments indicate that you might get an even more refined diagnosis if you make an appointment with a well-trained dog.
Researchers have begun training dogs to recognize the chemical smells produced by cancerous, unhealthy tissues. The training is simple: the dogs were rewarded when they sat or lay down next to the smells; they weren't rewarded when they didn't. Then the scientists collected the smells of cancer patients and patients without cancer, in small urine samples or by having them breathe into tubes able to catch exhaled molecules. Although the numbers of trained dogs are small, the results were big: the dogs could detect which of the patients had cancer. In one study, they only missed on 14 out of 1,272 attempts. In another small study with two dogs, they sniffed out a melanoma nearly every time. The latest studies show trained dogs can detect cancers of the skin, breast, bladder, and lungs at high rates.
Does this mean your dog will let you know when a small tumor develops in you? Probably not. What it indicates is that dogs are
able
to do so. You might smell different to them, but your changing smell might be gradual. Both you and your dog would need training: the dog to pay attention to the smell, you to pay attention to behaviors indicating your dog has found something.*
The smell of a dog

Since odor is so conspicuous to a dog, it gets great use socially. While we humans leave our scents behind inadvertently, dogs are not only advertent, they are profligate with their scents. It is as though dogs, realizing how well the odor of our bodies comes to stand for ourselves (even in our absence), determined to use this to their advantage. All canids—wild and domestic dogs and their relations—leave urine conspicuously splashed on all manner of object. Urine marking, as this method of communication is called, conveys a message—but it is more like note-leaving than a conversation. The message is left by one dog's rear end for retrieval by another's front end. Every dog owner is familiar with the raised-leg marking of fire hydrants, lampposts, trees, bushes, and sometimes the unlucky dog or bystander's pant leg. Most marked spots are high or prominent: better to be seen, and better for the odor in the urine (the pheromones and affiliated chemical stew) to be smelled. Dogs' bladders—sacs that serve no known purpose except as a holding pen for urine—allow for release of just a little urine at a time, allowing them to mark repeatedly and often.

And having left smells in their wake, they also come right up to investigate others' smells. From observations of the behavior of the sniffing dogs, it appears that the chemicals in the urine give information about, for females, sexual readiness, and for males, their social confidence. The prevailing myth is that the message is "this is mine": that dogs urinate to "mark territory." This idea was introduced by the great early-twentieth-century ethologist Konrad Lorenz. He formed a reasonable hypothesis: urine is the dog's colonial flag, planted where one claims ownership. But research in the fifty years since he proposed that theory has failed to bear that out as the exclusive, or even predominant, use of urine marking.
Research on free-ranging dogs in India, for instance, showed how dogs behave when left entirely to their own devices. Both sexes marked, but only 20 percent of the markings were "territorial"—on a boundary of a territory. Marking changed by seasons, and happened more often when courting or when scavenging. The "territory" notion is also belied by the simple fact that few dogs urinate around the interior corners of the house or apartment where they live. Instead, marking seems to leave information about who the urinator is, how often he walks by this spot in the neighborhood, his recent victories, and his interest in mating. In this way, the invisible pile of scents on the hydrant becomes a community center bulletin board, with old, deteriorating announcements and requests peeking out from underneath more recent posts of activities and successes. Those who visit more frequently wind up being at the top of the heap: a natural hierarchy is thus revealed. But the old messages still get read, and they still have information—one element of which is simply their age.
BOOK: Inside of a Dog: What Dogs See, Smell, and Know
4.31Mb size Format: txt, pdf, ePub
ads

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