How Dogs Explore the World Through Smell

“How can we feel sure that an old dog with an excellent memory and some power of imagination, as shown by his dreams, never reflects on his past pleasures or pains in the chase?”
–Charles Darwin,The Descent of Man, and Selection in Relation to Sex (1871)
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As far as party pieces go at the end of a lecture, Don Griffin’s was very hard to beat. TEDx would surely not have allowed such a stunt. Too much could go wrong. It could damage the lights or the camera equipment. It might cause a stampede.

But in the 1950s barely anyone had worries like these. And probably no one cared much about the poor bat, whose job it was to fly around wowing the crowd. Always leave them wanting more, goes the adage. Griffin did that…with a bat. Griffin—a rather preppie-looking, bespectacled professor—was something of an academic celebrity by then because he, alongside Robert Galambos, was co-discoverer of the incredible fact that bats used a form of sonar to navigate their surroundings in the dark. The bat emitted clicks, the pair discovered, that bounced off nearby objects and could be detected by the ears, allowing a bat to construct a three-dimensional map of its surroundings based on echoes. They called their discovery echolocation.

At first, the idea of echolocation had been laughed at by science but, by the 1950s, it had become not only accepted but positively lauded by zoologists. This was, after all, an entirely new way of looking at the world. Truly, theirs was a revolutionary discovery—one that changed our understanding of how animal sensory equipment could be rejigged for new purposes by the whittling force of natural selection.

For the purpose of our story, one particularly significant demonstration by Griffin took place at Rockefeller University (New York City) in one the dining rooms. At the end of his lecture Griffin released a single bat into the air so that the audience could marvel at the bat’s otherworldly dynamism, negotiating objects almost completely without the use of sight. It must have been enthralling for everyone (except perhaps the kitchen staff whose job it was to clean up). Sitting in the audience during this presentation, gazing at the bat in a state of total wonder, was a young visiting philosopher by the name of Thomas Nagel.

Just as Skinner had once watched Pavlov giving a lecture, Nagel was watching Griffin and the bat; he was awed and amazed by this new perspective on life. He watched the bat, rapt. He considered what it would be like to be that bat, flittering and flapping and twisting and turning about in the dining hall, its world calling back to him through the unimaginable medium of reflected sounds. The fact that Nagel could not put the bat’s experience into words is what made the experience all the more beautiful. He ended up carrying the strange thought experiment with him. As Nagel’s career developed, the experience with Griffin’s bats stayed. Two decades later, he would try again to put the bat’s experience into words—and fail in the most celebrated of ways.

Nagel’s 1974 essay “What Is It Like to Be a Bat?” posited a central immovable problem of science: that there can be no objective criteria that can help us know truly what it feels like to be in the mind of another animal. In the case of bats—living not in a world of colors or textures but in an environment made up of surfaces from which echoes emanate—it is almost impossible for us to imagine, being that our senses are heavily evolved towards visual stimuli, the most developed of our primate senses. Our brains just aren’t wired that way. Even for us to draw in our mind’s eye a world of echoes, we imagine a “wall” of sound—a kind of visual playing field of rebounding sound waves. It is impossible for us to get away from, no matter how we try.

Nagel’s essay didn’t remove animals of their agency to feel. Many animals might feel emotions in stronger and more profound ways than we can know. Instead, his argument is that we’ll never have a true understanding of what it must be like to be another animal because objective, reductionist thinking about consciousness is impossible with subjective minds like those that animals (including humans) possess. Nagel argued that, while scientific investigation might chisel away at our doubts about consciousness, it can never get us to the “facts beyond the reach of human concepts.”

After publishing the essay, which would become something of a sacred text to philosophers, the scientists and psychologists of the 1970s predictably divided into two warring camps: those who considered consciousness to be a viable area of study and those who certainly did not.

Does this mean we can never know what it is like to be a dog? Dogs are, in some way, not unlike bats. Like bats, their senses—the window through which their representation of the world is made—are skewed in a way that differs to our own, making our understanding their world that bit harder. Imagine, for a moment, being a dog and touring your kitchen by smell. Imagine pushing open the door and taking in the oily scent of the hinges. The oven gloves that, though washed many times, are still soiled by the smells of a hundred roast dinners. The cupboard in which the biscuits are kept. The tiny gap under the kitchen sideboard from which molecules pump out that leak out of a mouse that died two years ago and that no human ever knew was there. The smells that the houseplants release when humans brush past. The scent of the wet soil. The smell of dead leaves, of petrol, of wet patio slabs; the scent of ghostly night-time animals whose odors seep into the house via the gap in the window frame. The footprints of the child who visited last week. Where the food bowl goes. Where it has been. The exact location on the bowl where your beloved fingers have just gripped. If we could think like a dog, our daily lives would be taken up with tiny observations such as these. Stories would be told through smell. The vast majority of poems would be written about them. Our culture would feel very different indeed had we evolved from wolves rather than apes.

Even the act of sniffing in dogs belies an incredibly complex set of actions. In comparison, gathering light is rather a straightforward process. Our eyes are like satellite dishes that pick up its movement, absorbing a range of different wavelengths that penetrate and ricochet around in our atmosphere. Molecules of odor do not behave like light. They dance like unseen fairies upon tiny waves and eddies in the gaseous traffic jam within which our world plays out. They drift, they are diluted and they denature—decaying into other states, each with their own unique odors and their own evocations. To pick odor molecules out of the molecular maelstrom takes its own special hardware, which dogs keep quite literally front and center.

Dogs manage their sense of smell through some evolutionary innovations that are unavailable to many other mammals. First, when dogs inhale air, a fold of tissue splits the incoming air into two streams. The vast majority of air heads to the lungs, providing oxygen for respiration, but the other channel—perhaps 10 per cent or so—is directed nearer to the brain, to a region packed with curly bones called turbinates. The turbinates look a little like the air filters in a car and they act in a similar way too. As air moves through these thin tissues it collides with millions of receptor sites, each primed to receive a different kind of scent molecule.

Every time a scent molecule plugs into one of these receptors, a message pings to the brain: an odor is analyzed and a smell registered. It goes without saying that a dog’s sense of smell is vastly superior to our own, but it is their ability to detect tiny traces of odors that particularly sets dogs apart from many other mammals. Some dog breeds have noses that may be 10,000 to 100,000 times more sensitive than our own. Where we have about six million olfactory receptors in our noses, some breeds have something nearer 300 million. The part of the brain devoted to smells is proportionally gigantic—about forty times greater than our own.

Science writers have tried many ways to put into context how this compares to our own ability for smell. Dog expert and author Alexandra Horowitz argues it is like us being able to detect a teaspoon of sugar in two Olympic-sized swimming pools. Others argue it is like smelling a single rotting apple in two million barrels of fresh apples. I prefer to imagine the dog’s sense of smell in visual terms in a way I can better relate to: to be a dog in a world of smells would be like looking into the night sky and seeing 100,000 twinkling lights, each a distant star—exploding red giants or white dwarfs, asteroids, comets—the lights of time, pitching up and fading out. They would see it all, and they would surely pity the half-experience our senses allow us.

Even the exhalation of the dog is something to behold. As air coming out of the nose is forced sideways between the slits at the tip of the muzzle, this creates a drop in pressure in front of the nose that fresh air (containing new odors) rushes in to fill. This allows a dog, even on an outbreath, to keep the smells rolling in. In one study, a hunting dog in Norway was recorded to have maintained a continuous sniff for forty seconds, spanning thirty inhalations and exhalations.

Dogs can also wiggle their nostrils independently, to make the most of any and each passing smell. Evolutionarily, they’ve got it all. In the words of Jean Anthelme Brillat-Savarin, the father of food writing: “The sense of smell, like a faithful counsellor, foretells its character”—the same is true, only more so, in dogs.

It’s not that humans have a poor sense of smell. In fact, there are some smells we humans can detect at lower concentrations than dogs. Some plant leaves, for example, are meaty smells that dogs are most attuned to picking up. Dogs are highly sensitive, for instance, to the fatty acids given off from dead or dying animals.

It is clear that, in a funny sort of way, dogs can time-travel through smell. Because many odor molecules have a habit of breaking up and falling apart over a short period of time, dogs are able to judge from which the direction odor molecules are at their freshest and then make their movements accordingly. Like other mammals, most breeds are quite adept at following the path of a fleeing rodent whose movements are given away by a propensity for urination, for instance.

But there is yet more to their incredible senses than this. As of May 2020, we can add a new sense to the repertoire of dogs. We now know that their noses are able to detect thermal radiation too. Dogs, it appears, can heat-seek. To discover this, researchers from Sweden and Hungary first trained dogs to pick out identical objects with different temperatures. Then, using an MRI scanner, they looked at the brain function of thirteen different pet dogs when provided with neutral stimuli and with warm thermal stimuli.

When shown warmer stimuli, a tiny patch of neurons in the dogs’ left somatosensory cortex activated. This means dogs are in an exclusive club when it comes to extra-sensory endowments—some beetles, certain snakes and vampire bats are capable of the feat too. The extra-sensory talent may be particularly helpful when dogs are digging rodents out of burrows or out from under dense vegetation. It should be noted that this capacity to sense heat pales in significance to that of the nose’s primary function: to hoover up odors.

With the sense of smell occupying such a large region of the dog’s brain, it is obvious that a dog experiences the world in a different way to us—that their perceptions of the world differ from our own. In this sense, Nagel was absolutely correct. Like bats, their world is tuned in to a medium largely unavailable to us. But the question of consciousness remains significantly harder to pull apart. Can a dog know that it is alive? If so, is it conscious of its own existence? Can a dog plan for future events like we can? Can a dog reflect on, lament or feel shame for past actions? Exactly what does a dog’s daily experience of being alive feel like?

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Excerpted from Wonderdog: The Science of Dogs and Their Unique Friendship with Humans by Jules Howard. Copyright © 2022. Available from Pegasus Books.