Why Your Sense Of Smell Is Better Than You Might Think

May 11, 2017
Originally published on May 14, 2017 8:44 am

Smell, the thinking goes, is not our strongest sense. Our lowly noses are eclipsed by our ability to see the world around us, hear the sound of music and feel the touch of a caress. Even animals, we're taught, have a far more acute sense of smell than we do.

But one scientist argues the idea of an inferior sense of smell stems from a 19th-century myth.

When neuroscientist John McGann at Rutgers started comparing the sense of smell in rodents to what was known about the human sense of smell, he had an epiphany.

"Actually we have a really excellent sense of smell," he says. "There are quite a lot of experiments showing that the human sense of smell is pretty similar to what you can find with a rat or a mouse or a dog."

He published a paper about his findings Thursday in the journal Science.

McGann wondered why our noses got such a bad rap. He traced the idea back to the mid-1800s, and the work of a scientist named Paul Broca.

"He was interested in free will and he had this idea that smell was this very animalistic sense and that it compelled animals to have sex and feed," McGann says. "And humans, having free will, could choose how we responded to smells and presumably had a less strong or less special sense of smell than other animals."

Sigmund Freud picked up this idea, too, arguing that smell invoked instinctual sexual behavior in animals. In humans, however, Freud believed "the putative loss of smell caused sexual repression and enabled mental disorders, particularly if one 'took pleasure in smell,' " McGann writes in his paper.

As scientists in the 20th century started to explore the sense of smell, they interpreted their findings in a way that reinforced the idea that smell has been diminished in humans, as we stood upright and our noses came up off the ground.

One example is that humans have about 400 distinct smell receptors in our noses, compared with more like 1,000 receptors in rats. "But, in fact, 400 is an awful lot," argues McGann, "and, quite honestly, there are very few odors that are volatile enough to get into the air that humans can't smell."

In theory, we can distinguish tens of millions of unique smells, and maybe a lot more.

There have been a few nose-to-nose comparisons between humans and other mammals in the lab, but there's no consistent winner.

"Humans are best at some, and dogs are best at some and mice are best at some," McGann says. "It just depends on what the chemical is."

Case closed? Not by a long shot.

"If the argument is, 'We are better smellers than we think,' I assent," says Alexandra Horowitz, a psychology professor at Barnard College. "We are better smellers than we think."

But, Horowitz says, if the argument is that we are just as good as dogs at using the sense of smell, she doesn't buy it. She even wrote a book on the subject, titled Inside Of A Dog. She says there is no serious comparison between the performance of a scent-tracking dog and a person.

"It's one thing to talk about the capacity" to smell, she says. Clearly we have the capacity to distinguish between a large number of smells. But, she says, "Do we behaviorally do anything that's anywhere similar to these olfactory animals? No, we generally don't."

Horowitz says the one place where humans do excel is when we use our sense of smell to savor food. Subtle and pleasing aromas come into our nose from the back of our mouth.

"Without smell you can't taste, and that's a real loss," she says. "I will acknowledge that's something we're great at, maybe even better than dogs."

Horowitz says give credit where credit is due; there's no rule that says humans always have to come out ahead.

You can contact Richard Harris at rharris@npr.org.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

ROBERT SIEGEL, HOST:

Smell, the thinking goes, is not our strongest sense. Our lowly noses are eclipsed by our ability to see the world around us, to hear the sound of music, to feel the touch of a caress. Even animals, we're taught, have a far more acute sense of smell than we do. But a scientist is now arguing that that idea stems from a 19th century myth. NPR's Richard Harris reports.

RICHARD HARRIS, BYLINE: There are times when your sense of smell is front and center - for example, when strolling past food trucks like the ones that line up along a street near NPR headquarters.

MICHAEL LEWIS: You're smelling steam cabbage, jerk chicken, curried chicken and aroma from the rice and beans.

HARRIS: Michael Lewis owns the Reggae Vibes food truck. He says he gets so used to the aromas that he stops smelling them.

LEWIS: But our customer on the outside always come up and say, you know, in there smell real good and stuff (laughter), yeah.

HARRIS: It draws customers to you.

LEWIS: Oh, yeah, definitely - yeah, our smell, the music.

HARRIS: He's competing with the smells that come from a crab cake truck, one selling Mexican food and others down the line.

What am I smelling as I walk past your truck?

AMIN MUHAMMAD: It's the Indian spices. We have the lamb curry, chicken curry, chicken tikka masala, butter chicken, vegetarian chicken, lamb gyro.

HARRIS: Amin Muhammad stirs something frying in oil in his truck kitchen.

How many spices do you cook with? Do you know?

MUHAMMAD: Altogether, there's 11 to 13 spices.

HARRIS: Our noses have no trouble distinguishing between these aromas. In fact, in theory, we can distinguish tens of millions of different smells. Yet John McGann, a neuroscientist at Rutgers, says via Skype that humans have an inferiority complex when it comes to smell.

JOHN MCGANN: But actually we have a really excellent sense of smell, and there's quite a lot of experiments showing that in fact the human sense of smell is pretty similar to what you can find with a rat or a mouse or a dog.

HARRIS: McGann wondered why our noses got such a bad rap. As he writes in Science magazine, this idea took hold in the mid-1800s thanks to the work of a scientist named Paul Broca.

MCGANN: He was interested in free will, and he had this idea that smell was this very animalistic sense and that it kind of compelled animals to have sex and, you know, feed and do things. And humans, having free will, could choose how we responded to smells and therefore presumably had a less strong or less special sense of smell than other animals.

HARRIS: Sigmund Freud picked up on this idea, too.

MCGANN: Freud thought that people who took real pleasure in smell were more likely to be neurotic.

HARRIS: As scientists started to explore the sense of smell, they interpreted their findings to reinforce the idea that smell had been diminished in humans as we stood upright and our noses came up off the ground. One example is that humans have 400 distinct smell receptors in our noses compared with more than something like a thousand in rats.

MCGANN: But in fact, 400 is an awful lot, and there's - honestly, there's very few odors that are volatile enough to get into the air that humans can't smell.

HARRIS: And there have been a few nose-to-nose comparisons with humans and other mammals.

MCGANN: It seems like in this whole set of odors that have been tested, humans are best at some. And dogs are best at some, and mice are best at some. And it really just seems to depend on what the chemical is.

ALEXANDRA HOROWITZ: If the argument is, we're better smellers than we think, I absolutely assent. We are better smellers than we think.

HARRIS: But Alexandra Horowitz, a psychology professor at Barnard College, says if the argument is that we are just as good as, say, dogs at using the sense of smell, she doesn't buy it. There is no comparison between the performance of a scent-tracking dog and a person.

HOROWITZ: It's one thing to talk about capacity. You know, do we have the capacity to smell more than we do - yes. Do we behaviorally do anything that's anywhere similar to these olfactory animals? No, we generally don't.

HARRIS: Horowitz says the one place where humans do excel in using the sense of smell is when it comes into play as we taste food. Those aromas come into our nose from the back of our mouth.

HOROWITZ: Without smell, you can't taste, and that's a real loss. And I will acknowledge that that's something that we're great at, maybe even better than dogs, right? I'm not sure that they're tasting their food.

HARRIS: They certainly aren't savoring it in my experience (laughter).

HOROWITZ: Yeah.

HARRIS: Horowitz says credit where credit is due, and there's no rule that says humans always have to come out ahead. Richard Harris, NPR News. Transcript provided by NPR, Copyright NPR.