When I get home from work, after a cup of tea and a chat, I slump on the bed for a nap, a few seconds later there is a patter of paws on stairs. Something black pokes its nose round the door, pauses, leaps up. A heavy paw lands on my leg, a bony head thumps on my midriff and a tail beats a happy tattoo on the covers. It takes several minutes of sniffs, snorts and face-licks in response to my ruffles and pats before Alfie the labrador settles down, his velvet head next to mine, a picture of canine contentment.

For dog-owners, shared moments such as these reinforce our bond with our pets. They know our little ways, we know theirs, and we imagine that familiarity has bred understanding (on our part, at least) as well as affection. But this, according to Alexandra Horowitz, a cognitive scientist in New York, is presuming too much. A lot of what owners and trainers claim to “know” about dogs boils down, she says, to “theories generated from anecdotes and misapplied anthropomorphisms”.

Until recently science has been slow to fill in the gaps. When Horowitz began researching her book Inside of a Dog: What Dogs See, Smell and Know, most of her animal behaviourist peers were busy studying primates. They dismissed dogs as mere “simple, happy creatures”.

But wasn’t it remarkable that homo sapiens should choose to cohabit with an animal that shares all but a third of 1 per cent of its DNA with wolves?

Horowitz thought it was, and Inside of a Dog is the result. Her view is that, to understand dogs better , we must explore what it means to be a dog. “A perfect translation of every wag and woof may elude us,” she writes, “but simply looking closely will reveal a surprising amount” — as these extracts reveal.

What dogs smell

We humans tend not to spend a lot of time thinking about smelling. Smells are minor blips in our sensory day compared with the reams of visual information that we take in. But as we see the world, the dog smells it.

A dog sniff begins with muscles in the nostrils straining to draw a current of air into them. At the same time, the air already in the nose is pushed deeper into the nose or off through slits in the side. The slight wind generated by this exhale helps to pull more of the new scent in. This action is markedly different from human sniffing, with our clumsy “in through one nostril hole, out through the same hole” method.

Dogs are continually refreshing the scent in their nose, as though shifting their gaze to get another look.

Most purebreds and nearly all mutts have long muzzles in whose noses are labyrinths of channels lined with special skin tissue. This is entirely blanketed with tiny receptor sites. Human noses have about six million of these receptor sites; sheepdog noses, over 200 million; beagle noses, over 300 million. Dogs have more genes committed to coding olfactory cells, more cells, and more kinds of cells, able to detect more kinds of smells. The difference in the smell experience is exponential.

It is estimated that a beagle’s sense of smell may be millions of times more sensitive than ours. Next to them we are downright anosmic: smelling nothing. We might notice if our coffee has been sweetened with a teaspoon of sugar; a dog can detect a teaspoon of sugar diluted in a million gallons of water: two Olympic-sized pools full.

Humans stink. The human armpit is one of the most profound sources of odour produced by any animal; our breath is a confusing melody of smells; our genitals reek. Our skin is covered in sweat and sebaceous glands, which churn out fluid and oils holding our particular brand of scent. When we touch objects, we leave a bit of ourselves on them: a slough of skin. This is our signature odour.

As we move, we leave behind a trail of dead skin cells. The air is perfumed with our dehumidifying sweat. Added to this, we wear in odour what we’ve eaten today, whom we’ve kissed, what we’ve brushed against. Dogs find it incredibly easy to distinguish us by scent alone — and our aroma remains even after we have left; hence the “magical” powers of tracking dogs. These skilled sniffers see us in the clouds of molecules we leave behind.

Trained dogs don’t just notice a smell. They notice the change in a smell over time. The concentration of odour left on the ground by, say, a running footprint diminishes with every second that passes. 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.

A dog knows if you’ve had sex, smoked a cigarette, just had a snack, or just run a mile. They can also smell your emotions.

How does that menacing-looking dog smell our fear? We sweat under stress, and our perspiration carries a note of our odour on it. Adrenaline is unscented to us but not to the sensitive sniffer of the dog. Even simple increased blood flow brings chemicals more quickly to the skin.

Might dogs be able to detect chemicals indicating disease? Researchers have begun training dogs to recognise the chemical smells produced by cancerous tissues.In their first trial, using urine and breath samples, the number of trained dogs was small but the results were big: the dogs could detect which patients had cancer. In one study, they missed on only 14 out of 1,272 attempts. Trained dogs can detect cancers of the skin, breast, bladder and lungs at high rates.

Dogs’ bladders allow for release of just a little urine at a time, and it appears that the chemicals in the urine give information about, for females, sexual readiness, and for males, social confidence.

The prevailing myth is that dogs urinate to mark territory. But research on freeranging dogs in India showed that only 20 per cent of markings were territorial. Instead, marking seems to leave information about who the urinator is, how often he walks by a spot, his recent victories and interest in mating. In this way, the invisible pile of scents on the lamp-post becomes a community centre bulletin board.

What dogs hear

Our auditory range is from 20 hertz to 20 kilohertz: from the lowest pitch on the longest organ pipe to a squeak. But dogs can detect sounds up to 45 kilohertz.

A typical room is pulsing with high frequencies detectable by dogs. Think your bedroom is quiet? The crystal resonator used in digital alarm clocks emits a never-ending alarm of high-frequency pulses audible to canine ears. Dogs can hear the navigational chirping of rats behind your walls. And that fluorescent light? You may not hear its hum but your dog probably can.

Research suggests that dogs understand language to a limited degree, although to say that dogs understand words is a misnomer. If we were more sensitive to the sound of what we say to dogs, we might get better responses. High-pitched sounds mean something different from low sounds; rising sounds contrast with falling sounds.

What dogs see

For dogs, snout beats eyes and mouth beats ears. When a dog turns his head towards you, it is not so much to look at you with his eyes; rather, it is to let his nose look at you. The eyes just come along for the ride.

One element of the lives of wolves goes a long way to explaining the eyes they have evolved: eating. Most of their food runs away. It is active, and thus findable, only at dusk, dawn or night — so wolves are adept at spotting a change in the visual scene that indicates that something is moving. They also developed eyes that are especially sensitive in low light.

Dogs gather more light than we do. Once light enters the eye of a dog, it travels through the retina to a triangle of cells that reflect it back — so it hits the retina at least twice. Our eyes face forward and our retinas have foveae: areas with an extra abundance of photoreceptors. This makes us very good at seeing things in front of us in high detail, great focus and strong colour. By contrast, things in front of a dog’s face are visible to him but not as sharply in focus.

Dogs are not colour-blind but colour plays a much less important role for them, and their retinas are why. Humans have three kinds of cones, the photoreceptors responsible for our perception of details and colours: each fires to red, green or blue wavelengths. Dogs have only two: one is sensitive to blue and the other to greenish yellow. And they have fewer of even those than humans do.

Dogs make up for their dearth of cones with a battery of rods, the other kind of photoreceptor. Rods fire most in low-light situations and at changes in light densities, which is seen as motion. Dogs have up to three times as many rods as we do.

In all mammalian eyes, rods and cones make electrical activity out of light waves by means of a change of pigment in the cells. The rate at which cells do this is called the “flicker-fusion” rate: the number of snapshots of the world that the eyes take in every second. The flicker-fusion rate of humans is 60 images every second. Dogs have higher rate: 70 or 80 cycles a second.

Like film, the image on your (non-digital) TV is really a sequence of still shots sent quickly enough to fool our eyes into seeing a continuous stream. But it’s not fast enough for dog vision. They see the frames and the dark spaces in between them, too.

Finally, dogs see details that we cannot. That is because when humans enter a room, we take it all in in broad strokes: if everything is more or less where we expect it to be, we stop looking. Dogs are much more struck by what they actually see.

© Alexandra Horowitz 2010. Extracted from Inside of a Dog, to be published by Simon & Schuster tomorrow at £9.99. Available from TimesBookshop for £9.49 (0845 2712134; tolbooks.co.uk)

Other things you didn’t know about dogs

To stop a dog pursuing a bicycle with a predatory glint in his eye, one can simply interrupt the illusion: stop the bike. The chasing impulse triggered by the visual cells that detected the motion will itself let up.

Petting a dog can reduce your overactive sympathetic nervous system within minutes: a racing heart, high blood pressure, the sweats. Levels of endorphins (hormones that make us feel good) and oxytocin and prolactin (the hormones involved in social attachment) go up when we’re with dogs. Cortisol (stress hormone) levels go down.

Dog “kisses” are licks: slobbery licks to the face; exhaustive licking of the hand. But are they gestures of affection to the dog? Researchers of wild canids report that puppies lick the muzzle of their mother when she returns from a hunt to get her to regurgitate for them. Licking around the mouth seems to be the cue that stimulates her to vomit up some nice partially digested meat. Now the good news: the behaviour has become a ritualised greeting. In other words, now it is used to say hello.

Written by Alexaandra Horowitz, and reproduced from TimesOnline

Bookmark: