Why Your Sense Of Smell Is Better Than You Might Think

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.

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