Even though smell is the most direct of our senses and the 23,040 breaths we take daily drag in a universe of information — from the danger alert of a burning odor to the sweet nostalgia of an emotionally memorable scent — our olfactory powers are not even mediocre compared to a dog’s. The moist, spongy canine nose is merely the gateway into a remarkable master-machine which can detect smells in concentrations one hundred-millionth of what we humans require to smell something, and then transmute them into immensely dimensional and useful information about the world. So magnificent is the dog’s olfactory brawn — including the ability to sniff out skin, breast, bladder, and lung cancers with an astounding degree of accuracy and to literally smell fear — that to our primitive human perception it appears like nothing short of magic.
In the book — which also gave us the curious psychology of why a raincoat traumatizes your dog — Horowitz delves deeper into the impressive olfactory powers of canines, pointing out that the paltry six million sensory receptor sites in our noses are vastly eclipsed by the two to three hundred million in a dog’s nose. Not only do canines have manyfold more of these sophisticated information-processing units but they also have far more genes than we do dedicated to the coding of olfactory cells, as well as more kinds of those cells wired to detect more varieties of smells. Horowitz writes:
We humans tend not to spend a lot of time thinking about smelling. Smells are minor blips in our sensory day compared to the reams of visual information that we take in and obsess over in every moment.
Not only are we not always smelling, but when we do notice a smell it is usually because it is a good smell, or a bad one: it’s rarely just a source of information. We find most odors either alluring or repulsive; few have the neutral character that visual perceptions do… As we see the world, the dog smells it. The dog’s universe is a stratum of complex odors. The world of scents is at least as rich as the world of sight.
But at least as remarkable as the dog’s olfactory neurocircuitry — and as superior to our primitive human version — is the physical act of sniffing itself:
Few have looked closely at exactly what happens in a sniff. But recently some researchers have used a specialized photographic method that shows air flow in order to detect when, and how, dogs are sniffing… The sniff begins with muscles in the nostrils straining to draw a current of air into them — this allows a large amount of any air-based odorant to enter the nose. At the same time, the air already in the nose has to be displaced. Again, the nostrils quiver slightly to push the present air deeper into the nose, or off through slits in the side of the nose and backward, out the nose and out of the way. In this way, inhaled odors don’t need to jostle with the air already in the nose for access to the lining of the nose. Here’s why this is particularly special: the photography also reveals that the slight wind generated by the exhale in fact helps to pull more of the new scent in, by creating a current of air over it.
This action is markedly different from human sniffing, with our clumsy “in through one nostril hole, out through the same hole” method. If we want to get a good smell of something, we have to sniff-hyperventilate, inhaling repeatedly without strongly exhaling. Dogs naturally create tiny wind currents in exhalations that hurry the inhalations in. So for dogs, the sniff includes an exhaled component that helps the sniffer smell. This is visible: watch for a small puff of dust rising up from the ground as a dog investigates it with his nose.
Horowitz puts the gaping mismatch of abilities in pause-giving perspective:
We might notice if our coffee’s 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.
Inside of a Dog is an endlessly fascinating read in its totality. Complement it with Mary Oliver’s impossibly wonderful poems about dogs and this sweet animated ode to what dogs teach us about the meaning of life, then redeem some of your human sensory dignity with the not entirely unimpressive science of how our own sense of smell works.
For more treats from TED-Ed, see the science of why music benefits your brain more than any other activity, how to spot liars, and why bees build perfect hexagons.