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Dogs Smell Time

Dogs Smell Time

Can you smell time? Your dog can.

On a very basic level, so can you: When you crack the lid on that old quart of milk, tentatively sniff and—peeyouu!—promptly dump that foul stuff down the sink, you are, in effect, smelling time. Specifically, you can smell that far too much time has elapsed since that milk was fresh.

But a dog can smell time with a sophistication that puts our simple sniffers to shame. “Odors exist in time, and dogs perceive that,” explains cognitive scientist and canine researcher Alexandra Horowitz of Columbia University. “Dogs use smell to ‘tell time,’ in some sense, because a more recently laid odor smells stronger, and an older odor smells weaker.”

A dog’s nose is a notoriously sensitive piece of equipment. With up to 300 million olfactory receptors compared to our lousy 5 million, a dog can detect a single teaspoon of sugar dissolved into a million gallons of water, the equivalent of two Olympic-sized swimming pools. Unlike us, dogs are able to take in scent continuously, even as they exhale. What’s more, a dog’s nostrils are smaller than the distance between them, effectively giving dogs “stereo” sniffing power that carries subtle grades of information, including directionality.

Together, these features add up to a formidable nasal organ that supplies far more information than our own: not just what, but also who, when, where, how, which way, and even what next?

Expert tracking dogs offer an extreme example of this scent-based detective work. Not only can such dogs detect corpses submerged in over 80 feet of water, they can smell trails that are up to a week old, and detect the directionality of tracks—without any visual cues—from just a few steps. Researchers experimenting with scent trails left on carpet squares found that a good tracking dog needs just five footsteps to reliably decide which way a trail leads, which means a dog can smell the slightly stronger scent left by a footstep that was made just a second or two later than another.

Even “ordinary” non-tracking dogs reach into the past through scent. When you arrive home, your dog can take one whiff of you and get the entire story of your day—where you went, how long ago, who and what you were with—including details that you yourself may not even be aware of, like the fact that there was one stray mushroom on that pepperoni pizza you had for lunch.

A dog’s very experience of time is probably olfactory, argues Horowitz, as time elapsing through the day is probably marked by subtle shifts in the olfactory environment. What’s more, a dog’s ability to smell time extends into the future, insofar as a dog can “smell what’s coming” on the breeze, and even predict seizures or detect cancer and other diseases before they can be otherwise diagnosed.

“It’s as though dogs have a larger olfactory window on the present,” says Horowitz, a window far wider than our own, with “a shadow of the past and a ring of the future in it.”

Maybe next time you’ll be a little more patient when your furry friend wants to stop for a sniff.