Dogs Live in the Past
We are well aware that dogs have an ultra-keen sense of smell. They’re sniffing everything: the floor, plants, and most awkwardly, the crotch of your houseguest.
But each inhale they take is more than just a smell. It’s a massive download of data. When we look at how dogs process scent, we quickly see how differently they perceive the world around them.
A Nose That Knows: Dogs Vs Humans
Dogs can detect about 50 times the number of scents that a human can, with an olfactory brain center that is about 40 times larger than that of humans. They can also smell things up to 2 miles away and detect individual ingredients in a stew.
Figure: Olfactory Brain Center Comparison, Human vs. Dog
As humans, we can only imagine what it might be like to be a dog. If you try really hard, you can put yourself in the paws of a dog, and imagine walking through the city streets or along nature trails with bionic noses. On a breezy day, you could detect specific people up to 2 miles away.
Canines sniff through each nostril separately, triangulating the position of anything emitting odors, building a “scent map” of the world, just as we do with vision. These maps would be indistinct, clouds of markers that shift with the wind and fade with time. The world of scent is fuzzy and uncertain, unlike our sharp vision, which is relatively crisp. Yet, despite the fuzziness, if we were like dogs, we could find a child lost in the woods, where we dropped our keys out on a hike, or what we did with our precious phone, even from far away. That’s more than we can say for our sight.
Built For Smelling: Dog Scent-Detecting Physiology
The dog’s nose has a complex scent-detecting physiology. Inside, it’s filled with thin, curled bones called turbinates that create a huge surface area that’s lined with smell-sensitive cells. When a dog sniffs, the air is split into two paths: one for breathing and one just for smelling, so that the breathing doesn’t interfere with their superior scent-detection. They also exhale air through special slits in the sides of their nose to stir up more scent particles. The air inhaled for smelling is deposited in the olfactory region, where it accumulates without being expelled. Their brains are wired to process these deposited smells in incredible detail. This helps them recognize people, animals, and other smelly things in ways we can’t, with a memory of that scent that lasts a long time.
Figure: Dog nasal cavity with turbinates, key to scent detection. Adapted from Buzek et al., 2022, Animals, 12(4), 517. CC BY 4.0 (https://doi.org/10.3390/ani12040517).
The Incredible Things That Dogs Can Smell
We are all familiar with drug-sniffing dogs from TV shows and the food-sniffing beagles at international airports, as well as search and rescue dogs that find people lost in the wilderness. But their sense of smell goes far beyond that. An increasing number of studies are being conducted using medical detection dogs to identify infectious and non-infectious diseases. While those studies suffer from a lack of standardization in training and data collection, their success rates range from 19% to 99%. They demonstrated that dogs can detect certain cancers (including colon, lung, bladder, breast, ovarian, and prostate), seizures, and diabetes, as well as infectious diseases like malaria, bovine viral diarrhea, and bacterial infections. Imagine going to Dr. Rex the Dog for a diagnosis!
What Dogs Can’t See
However, when we compare their sense of sight, we quickly see they can’t see like we can. Dogs, like most mammals, are dichromats and can’t see the red colors that humans can. This is why, incidentally, the orange color of a tiger appears camouflaged to their prey even though it does not to us. But we’ll save that discussion for an article on camouflage and the color spectrum.
Figure adapted from Fennell et al. (2019), Journal of the Royal Society Interface, 16(154), 20190183. Licensed under CC BY 4.0. https://doi.org/10.1098/rsif.2019.0183
While the dog’s visual world is less rich in terms of wavelengths of light, they can still detect motion much better than we can. The flick of a squirrel’s tail pops out to them much more than it does to us.
Dogs Can Smell The Past
With their poor visual acuity, I started thinking about how a dog moves through the world, with this incredibly enhanced sense of smell, and imagined what it would be like to be a dog. I realized this: dogs can smell the past.
It would be like walking into a room and seeing what happened two weeks ago. Like faint after images of a friend visiting the house last week, with visual images overlaid on top of one another, blurring the boundaries of time. Canines would have an entirely different perception of time than we do, like living in the past while being in the present.
While some people think dogs can’t tell time, they actually “smell time.” Search and rescue dogs are well-known for tracking the scent of missing people. But when they find a trail, how do they know which way to go? They sniff in each direction and follow the strongest scent. Even if we could somehow smell their trail, we could never detect which is just barely weaker, yet dogs know not to follow it because it’s of the past.
However, dogs can also be trained to locate the past. How far back can dogs smell? We don’t yet know. Cadaver dogs used in criminal investigations have even helped archeologists successfully discover prehistoric burial sites dating as far back as the Iron Age. How’s that for a nose for the past?
Final Thoughts: Imagine the Life of a Dog
So, with this olfactory information in mind, I challenge you to take a walk like a dog. Not on all fours (unless that’s your jam), but simply imagining the world with that slippage of time. Where the present moment slowly fades away, becoming just one more layer in a deeper scent-marked story that combines what happened days, months, or even years ago, all lingering like an after-memory.