Myths and mysteries of the olfactory sense

In his great work, “In Search of Lost Time,” also known as “Remembrance of Things Past,” the French writer Marcel Proust cited the role of the senses in our most vivid memories: “When nothing else subsists from the past, after the people are dead, after the things are broken and scattered, the smell and taste of things remain poised a long time, like souls bearing resiliently on tiny and almost impalpable drops of their essence.”

In the past few weeks, watching the world slowly shake off its winter torpor, I’ve spent lots of time anticipating the sweet aromas of spring—growing grass and flowers, and the scent of the earth itself, nearly ripe for its reproductive rite.

Why do we like some smells, and dislike others? You may have assumed these preferences are biologically dictated—that we’re instinctively repelled by the smell of rotting fish, for example, to keep us from eating it. It makes sense, doesn’t it? Nature equips us with lots of evolutionary protections, it stands to reason that our sense of smell also would serve as a self-preserving mechanism. Of course, that wouldn’t account for why we love certain scents, like lilacs, or ocean breezes, or hot coffee, or ripe strawberries. So how do we sniff out the secrets of smell?

Research suggests that the human olfactory sense—the smells we love, and those we loathe—have little to no biological imperative. The late psychologist Trygg Engen of Brown University, author of “Odor Sensation and Memory,” argued that human beings like or dislike smells for no other reason than their associations with memory.

Engen said our response to odors is more “nurture” than “nature.” He said all smells are neutral, and our perception depends solely on good or bad associations from the past.

Dr. Rachel Herz, also of Brown, concurs, and says the theory is borne out by the reaction of babies to new smells. Infants “show wariness when exposed to unfamiliar odors, regardless of whether the odors are classi?ed as pleasant or unpleasant by adults,” Herz wrote. “Knowing what smells we like and dislike, and why you and I may not agree on how they smell, comes about because of our speci?c personal and cultural histories and experiences.”

Nothing seems more counterintuitive, and frankly, I’m not sure I buy it, because it would make us oddballs in the mammalian family. Dogs rely on their noses to navigate, communicate, mate and evaluate. Skunks repel predators with their powerful smell; there are few who would argue that the smell of a skunk is purely subjective. Our friends the turkey vultures are attracted to the gases that emanate from dead animals; when they catch a whiff of that gas in the air, they swoop down for a tasty roadside feast.

Similarly, when you or I pass a Dunkin Donuts, or a pancake joint, or a pizza parlor, or a fast-food drive-in, it’s the smell that first draws us in. How could our sense of smell be meaningless, or subjective? We lose our enjoyment of food when illness hampers our ability to smell it. The condition known as anosmia, the actual loss of the sense of smell, leads to depression, anxiety, frustration and even the loss of sex drive.

And how about the hullabaloo a few years back about pheromones, the subtle undercurrents of scent that supposedly attract one person to another, trumping more obvious attractions like appearance, education, youth and status?

Then again, maybe Engen and Herz are right, or partly right. For instance, I dislike the taste of beer, but I love the smell. Why? Because it reminds me of my dad, who always had a few “cold-brewed Ballantines” in the evening when I was a kid. I wouldn’t dream of smoking a cigar, but I rather like the smell, because it reminds me of my late great-uncle Harry Hackman, to whom I was devoted as a very small girl. I love the smell of musty old houses and attics (they remind me of my grandmother’s farm), and the smells of old paper, Crayola crayons and Silly Putty (which take me right back to grade school). I also love the smell of incense, which can transport me instantly to the church of my youth. For some reason, I adore the smell of hot tar. Maybe it’s because I like construction workers. Who knows?

It’s an interesting question to ponder as spring nears. Is our delight at the subtle scent of daffodils and lilies of the valley biologically determined, a matter of taste, or a response to memory? Maybe it’s a little of each.