Why we don't smell more

Our olfactory sense is highly developed and underused.

Published July 28, 1999 4:00PM (EDT)

The late physicist Richard Feynman had among his party tricks a bloodhound act. While he was out of the room, someone would pick up and handle just one bottle or can in a six-pack. Or three people would each handle one book, and replace them on the shelf. Feynman would come back, smell everybody's hands, smell the books and pick out the books that had been handled, and then the people who had handled them. "It was easy," Feynman related. "It's hard to explain, because we're not used to saying things about it. You put each book up to your nose and sniff a few times, and you can tell."

The onlookers suspected Feynman (with good reason) of being capable of some pretty sneaky tricks. Did he have a confederate who signaled which books had been touched? Who was the stooge? But then he'd challenge them to try -- and if they tried, they could usually do it too.

But unless Richard Feynman is standing there goading them, people usually don't sniff books to see who's handled them, even if they want to know. It simply never occurs to us. And while studies have shown that mothers can recognize by smell which of several identical T-shirts has been worn by their own baby, as opposed to someone else's baby; and that babies in turn can distinguish the smell of T-shirts worn by their own mothers -- it's only because the nice people in the white coats ask them to try.

Most of us have a much better sense of smell than we realize. "When faced with formidable tasks, humans do quite well," says researcher Charles Wysocki of the Monell Chemical Senses Center, who studies the behavior and genetics of olfaction, among other areas. "They don't have to be trained or anything, they can just do it."

We can, but we hardly ever do. And if we do, people look at us strangely. You may think I'm strange just for writing about smell: I certainly think it's strange that you're reading this.

My friend Cynthia smells bread. "I want to know more about it before I eat it," is her sinister explanation. I don't sniff bread, but I sniff produce, and I learn a lot. A strawberry that doesn't smell like a strawberry is going to be one of those berries that resemble damp Styrofoam. A peach that doesn't smell peachy won't taste peachy. And smelling the stem end of the cantaloupe is a sure way to find a good one. "I never thought to do that," says Cynthia, wonderingly. I know she thinks I'm weird.

Indeed, I never see anyone else huffing those good produce scents, so I do it furtively. Casually. I raise the cantaloupe to my level, rather than stooping low, hoping that people will think I'm just eyeballing the fruit, a perfectly respectable thing to do.

The convention seems to be that we cannot smell anything unless it is drawn to our attention and we unbend to make a deliberate effort. It is acceptable to direct someone to a pleasant natural smell: "Take a breath of that ocean air," "Oh, smell that sagebrush." "Do I smell coffee?" It is somewhat acceptable to comment on an unpleasant smell if it's nonliving -- bus exhaust, roofing tar, cannon smoke.

Sniffing people or produce is thought to imply that an unpleasant odor has been detected, so it is unacceptable to note the smells of living things, even if the smells are nice. (In fact, it may be unacceptable to acknowledge that people might smell nice without the whole-hearted 24-hour aid of the fragrance industry.) "I can see you from here" and "I can hear you from here" are permissible remarks, but "I can smell you from here" usually is not.

Some years ago, scientists studying inbred strains of mice discovered that the mice seemed to be able to tell which mice had the same H2 antigens on their white blood cells and which had different H2 antigens. The mice preferred mates with different H2 antigens, and experiments established that they could tell from the way the other mice smelled. But it took a while before someone realized that people could do it. Goaded by co-workers, scientists took the sniff test and discovered they had the ability too. The different strains of mice looked identical, sounded identical, but smelled different. But who goes into science to sniff mice?

Since the H2 antigens on mouse cells are the equivalent of the HLA (human leukocyte antigen) markers on human cells, it seems that people ought to be able to do in each other what we can do in mice, and various studies are under way to see if people really avoid marrying people whose HLA markers are similar. At present, when organ and marrow donors are sought, it is done through a series of costly blood tests -- but would people be ready to replace the initial round of tests with a thorough sniffing? Would you be smelled by strangers to save a life?

I keep hearing that it's cultural. Other cultures aren't so hung up about the ickiness of smells, people say. "Which other cultures?" I ask, because I really want to know, and because I have these fantasies about going on exciting fact-finding trips to foreign parts, but no one ever seems to be sure. "Primitive cultures," they say vaguely. I can just hear me telling a travel agent that I want to go to some place where the primitive people smell things more. I would be bounced from Ecotourism HQ faster than the World Bank Executive Retreat.

Once upon a time, it seems, our ancestors smelled all kinds of things. The parts of the brain that analyze smell are old and seem rather archaic. In fact, the whole system seems kind of zany: odorants -- little particles of scent -- drift into your nose, where they encounter the olfactory epithelium at the back of your nose. The olfactory epithelium is a waving sea of nerve endings, each with a singular odor receptor on the end. If enough odorants set off odor receptors, a message travels up the neuron. Any particular odor may be setting off more than one kind of olfactory receptor, which respond to different parts of molecules. Unlike other sensory neurons, olfactory neurons get replaced every month or two -- it's important to stay in top sniffing shape. And smell data gets a special pass to the cortex without having to pass through the thalamus like other sensory data. Must be a grandfather clause.

Smells are complicated. In the smell of coffee, Wysocki says, "there are over 100 molecules that are impinging upon the receptors in the nose. But the brain is able to put all that together and formulate a response that says, 'Ah, coffee!'"

It seems theoretically possible that you could have two people staggering into the kitchen of a morning, whining for coffee, and each could be detecting only 50 odorants -- and the two could be detecting two different sets of 50 odorants. "Ah, coffee!"

The sense of smell can be trained. "People can be sensitized to odors that in the past they couldn't smell," Wysocki says. The most efficient way to do this is to be exposed to the relevant odors for a few minutes a day -- longer than that and smell fatigue sets in -- over a period of weeks.

In 1991 researchers found that humans have around 1,000 genes coding for different odor receptors. Since each odor can set off more than one receptor in various combinations, this implied the ability to sense far more than 1,000 scents. "Given that mammalian DNA probably contains around 100,000 genes, this finding indicates that 1 percent of our genes are devoted to the detection of odors, making this the largest gene family thus far identified in mammals," wrote molecular biologist Richard Axel.

But recently other researchers took a close look at those genes and discovered that about 70 percent of them contain stop codons. In other words, the gene -- which provides the instructions for making the protein that is the odor receptor -- suddenly stops in the middle of the instruction booklet and says, "Oh, forget it. It's too complicated. Don't bother making it. It's not like anyone ever needs to smell enraged saber-tooth cats anymore. I'll just sit here in the genome and sulk."

Genes like these are called pseudogenes. It's not yet known whether the same 70 percent of genes are knocked out in each person. So that means we only have on the order of 300 odor receptors to play around with.

That still should leave us able to detect quite a few smells, if we're willing to try. Of course, maybe we smell more than we realize. "People don't know how much we use it, until we lose it," Wysocki says. Chemical exposure (sometimes including pool chlorine), illness, nasal polyps or head trauma can cause anosmia, the loss of smell. "When people do lose their sense of smell, some could care less: 'So I've lost my sense of smell. Big deal.' Some people are devastated. Some people have considered suicide," Wysocki says.

So maybe there's more going on than it seems, but we don't notice it. We don't talk about it much either. Many people have commented that the English vocabulary for talking about smell is feeble. (Rumor has it that unspecified primitive languages have better vocabularies.) With few exceptions, describing smell is a series of comparisons. "Like a piney smell, but more earthy." "Sort of a tea rose scent, with a musky base note." "Ah, coffee! But not quite."

Part of the problem is the analog nature of smell. We don't need 300 different kinds of receptors to detect colors or notes. Odors don't have wavelengths, although they have intensities. I asked Wysocki why we don't have a better vocabulary for smell. "We could if it were important," he said. We also discussed the unfortunate ambiguity of the verb to smell, which means that to say, "I smell a lot" is to risk ridicule. Do the researchers at Monell have a special verb to get around this? Do they say, 'I olfact a lot'? Wysocki pondered. "I think we don't use 'smell.' For the most part we use something like 'perceive.'"

Somewhere along the line we gave up on smell. I mean perceiving odor. We gave up devoting all those genes to it, gave up on including it in the conversation, gave up on using it much and began to pretend not to use it at all. It may be that some of the things we were using it for, like gathering personal information about each other, are the real taboo. The sense of smell is disturbingly closely related to the sensing of pheromones, which carry all kinds of information in other animals, such as mice, critically important messages like "R U M or F?" and "I am in heat -- somebody do something" and "Nobody around here better have any babies but me or I will bite them SO HARD."

Just how much use humans make of pheromones is still highly unclear, which doesn't mean that you can't buy dozens of products promising to be a-bubble with them, which will raise your self esteem, mood and popularity to that of a mouse. Aside from loose effects on menstrual synchrony, most of these pheromonal effects have yet to be proved. But if I were picking up information about, say, other people's sexual charisma via pheromones, wouldn't it be rather rude of me to advertise that fact with my incessant sniffing? Or maybe our species has found that we can get along just fine without knowing everybody's personal business.

Social speculation aside, our big mistake was probably standing up. Useful as that has been in so many ways -- need I say how pleased I am about being able to grab stuff off the top of the refrigerator? -- it has torn us away from our roots as sniffers and snufflers.

When I take my dog for a walk, my nose is more than a yard from the ground (maybe it's two yards! maybe I'm a supermodel!), while his is mere inches away. He can easily lower his nose to the ground to smell some interesting object. All he has to do is plant his feet so I don't drag him away, dip his neck and inhale deeply.

I, on the other hand, should I wish to sniff the same intriguing object, must glance around furtively, hitch up my clothing, kneel with care (this is after all a sidewalk with interesting objects on it), fold up like a jackknife and shove the jealous dog away before I can sample the mysterious fumes. (Then, in order to explain my actions to anyone who might be driving by, I must loudly exclaim, "Oh, here's my contact lens!" "A twenty! This is my lucky day!" or "Quickly, my alien master! Resume the form of a dog so that no one suspects your presence on our planet!")

In the 1980s, biologist George Schaller traveled to a remote mountainous part of China to study pandas. One day after about a year, he was following a panda's tracks along a snowy trail. The tracks showed clearly that the panda had swerved over to a fir tree and gotten quite involved with it. Puzzled, Schaller examined the tree and found that it had been rubbed, clawed and smeared with a dark secretion. "Bending close to smell it, I could detect a sweetly acidic odor. Suddenly I realized that this was a scent-post on which pandas had repeatedly deposited their personal odor. How totally stupid I felt. For months I had passed this tree without noting the distinctive marks on it ... Walking that ridge I had used my eyes, not my feeble nose. How would I ever understand pandas? They moved from odor to odor, the air filled with important messages where I detected nothing."

Clearly, Schaller wouldn't have made that mistake if he'd had Richard Feynman along. I like to think of the two great scientists snuffling along the trail, using their odor receptors to the fullest, gathering vital data, and then returning to camp, tired but with the feeling of a job well done, changing into T-shirts that they would never get mixed up. Ah, coffee!

By Susan McCarthy

Susan McCarthy is a San Francisco freelance writer and the author, with Jeffrey Masson, of "When Elephants Weep: The Emotional Lives of Animals."

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