The Smell of Time Passing?

The question “what time is it?” is one that we often have to ask ourselves. Our lives may be busy and we have places to go, people to see, and stuff to do. To ensure we’re at the right place at the right time, we need to know what time it is. And that’s not all that hard. We have clocks in our rooms, watches on our wrists, and of course, smartphones which have the time front-and-center, even when they’re locked. If you want to know what time it is, all you need is one of those tools and the ability to read and understand the numbers.

Almost all of us can do that. And as a result, we can predict when routine things that happen in our daily lives. For example, we can roughly estimate when our loves one will come home from work or school — all we need to do is know that person’s typical return time and look at a clock.

But we’re not alone on our ability to anticipate when mom or dad come home. Dogs can do it, too. And no, they’re not somehow able to read a clock face.

In 2022, NPR ran a story about Donut, a hound mix, and his owner, Matt Doucleff. Matt’s wife, Michaeleen, recounted a story that she heard whenever the couple visited Matt’s parents: “Matt had Donut all through his childhood, from elementary school through high school. So during the day, Donut spent most of the time inside, right? But then, every school day, Donut would do something uncanny – at exactly the same time, right before the school bus brought Matt home [Donut would run to the door to greet him].” So how did he know when Matt was on his way home?

Donut probably wasn’t using his eyes. Most likely, he was using his nose.

Dogs have a sense of smell that far eclipses that of humans, as is well documented. (Per Wikipedia’s editors, “The typical dog’s nose is 100,000 to 1 million times as sensitive as a human’s, and the most sensitive breed, the bloodhound, has a sense of smell which can be up to 100 million times as sensitive. Additionally, dogs have much larger olfactory mucosa and a larger part of the brain dedicated to odors.” And in this case, it’s the odors we humans emit that our canine friends are keying in on.) Alexandra Horowitz, the founder of the Dog Cognition Lab at Barnard College, explained the theory to the American Kennel Club:

“Smells in a room change as the day goes on. Hot air rises, and it usually rises in currents along the walls and will rise to the ceiling and go kind of to the center of the room and drop. If we were able to visualize the movement of air through the day, what we’re really visualizing is the movement of odor through the day.” And as the the day goes on, the scents that the dog associates with us individually fade, as Michaeleen Doucleff summarized for NPR:

So you can imagine, back in the ’90s, when Matt was getting ready for school in the morning, his house filled with his unique scents, from his stinky socks to the new shampoo he used, and those smells hung around even after he went to school.

[ . . . ]

Then at 3 p.m. each day, when the bus was on its way, the smell of Matt probably reached about the same level every day, and Donut would have noticed that level.

Per Horowitz (who also spoke with NPR), “Given that things like school buses arrive at about the same time every day, pretty quickly they would associate a weaker odor with the person being about to return.” Donut, it seemed, learned to smell time.

This isn’t the first time that this theory has been piloted. In 2014, the BBC ran a hardly scientific, but still pretty cool experiment at the home of Christine and Johnny, a couple with a pretty regular routine — they’d leave their home and return at roughly the same time every day, leaving their dog, Jazz, to do whatever dogs do during the day. Christine arrived at home at about 4 pm and Johnny at about 5 pm, and, as the BBC shared in this video, “every evening at around 4:40, twenty minutes before Johnny comes home, Jazz always leaps up onto the sofa, as if he’s waiting for him.” (The screenshot above shows Jazz waiting at roughly the same time over four different days.) To see if this weakened-odor theory held weight, the BBC collected some of Johnny’s smelly t-shirts and placed them in the room at around 4 pm. And on that day, as the video shows, Jazz wasn’t at the ready when Johnny came home. Or, in the words of the BBC, “to Jazz, it seems to come as a complete surprise.”

Bonus fact: Dogs are on the front lines in helping conservationists weed out invasive species. The Scotch broom, for example, is a plant that is native to western and central Europe but considered a menace in North America, where it can spread unchecked and, per Bright Vibes, “destroys grasslands, poisons animals and fuels forest fires.” The plant’s seeds are viable for up to ten years, so the only way to stop the broom from spreading is to find each and every seed — something human eyes can’t do. But dogs’ noses can. Joshua Beese, a dog trainer who teaches dogs how to leverage their sense of smell to further conservation efforts, explained the situation to Reasons to Be Cheerful: “[The seeds are] easy to miss, but not to the dogs. They can find invasive seeds hidden under bushes — places you wouldn’t think of going. You’d have to crawl on your hands and knees. And the dogs cover a lot of territory.”

From the Archives: Smell Ya Later?: Why can’t we smell as well as dogs? Chances are, it’s because our sense of smell has actually devolved over generations.