The Wonders of Odors in the Air

May 12, 2014 | Posted in: Science

Allegory of the sense of smell, Jan Brueghel & Peter Rubens, 1618.

Allegory of the Sense of Smell, Jan Brueghel & Peter Rubens, 1618.

“Odors have a power of persuasion stronger than that of words, appearances, emotions, or will. The persuasive power of an odor cannot be fended off, it enters into us like breath into our lungs, it fills us up, imbues us totally. There is no remedy for it.” Patrick Süskind


“Smell is a potent wizard that transports us across thousands of miles and all the years we have lived… odors, instantaneous and fleeting, cause my heart to dilate joyously or contract with remembered grief. Even as I think of smells, my nose is full of scents that start awake sweet memories of summers gone and ripening fields far away.” Helen Keller


Blooming roses, fresh baked cookies, a gin martini garnished with green olives, lathered soap, fresh cut grass, drying lavender, wood fires, gas stations, swimming pools, a loved one’s perfume: all of these phenomena are the purveyors of potent scents, so powerful that we can still recall the smell even if we could hardly describe it. Vivid smells are rarer in the frozen cold of winter and the sun bleached days of summer, but spring and autumn, ah these are the seasons for scents! And, since odor molecules require moisture and air in order to trigger our nasal receptors, once more we owe the atmosphere gratitude, this time for providing us with the world of olfactory delights and warnings.

“Each day, we breathe about 23,040 times and move around 438 cubic feet of air. It takes us about five seconds to breathe — two seconds to inhale and three seconds to exhale — and, in that time, molecules of odor flood through our systems. Inhaling and exhaling, we smell odors. Smells coat us, swirl around us, enter our bodies, emanate from us. We live in a constant wash of them.”  Diane Ackerman, A Natural History of the Senses

Smell is by far the most widely underrated of the five senses nature endowed us with. For most people, little attention is given to the endless parade of subtle aromas that fill our every inhale. It’s true that it’s been long since smell was a vital contributor to human survival, with vision and hearing by far dominating our sensory experience and providing the vital information regarding danger, food, shelter, and potential mates. But smell was the first of the senses to evolve and holds a special connection with memory:

“Early in our evolution we didn’t travel for pleasure, only for food, and smell was essential. Many forms of sea life must sit and wait for food to brush up against them or stray within their tentacled grasp. But, guided by smell, we became nomads who could go out and search for food, hunt it, even choose what we had a hankering for. In our early, fishier versions of humankind, we also used smell to find a mate or detect the arrival of a barracuda. And it was an invaluable tester, allowing us to prevent something poisonous from entering our mouths and the delicate, closed system of our bodies. Smell was the first of our senses, and it was so successful that in time the small lump of olfactory tissue atop the nerve cord grew into a brain. Our cerebral hemispheres were originally buds from the olfactory stalks. We think because we smelled.Ackerman

Most other species still flex their full olfactory prowess, and chemical communication in the form of odors is an invisible world overflowing with gossip, threats, commands, and invitations:

“The world is awash in perfumes. Some are specific to the creature that emits and receives them. Some can be eavesdropped by others. Some are intentionally faked by predators to attract their prey. All depend on the physical movement of chemicals or groups of chemicals through the air from sender to receiver. This exchange of signals—what in mammals like us would be called sniffing, but in others involves the flick of a tongue, the rustle of an antenna, or the rubbing together of heads—is by far the most common form of communication among the living.”
William Bryant Logan, Air: The Restless Shaper of the World

Chrysanthemum, Katsushika Hokusai. Enticing pollinators with floral odors in the air.

Chrysanthemum, Katsushika Hokusai.

Plants, seemingly silent and immobile, are the peerless alchemists of the chemical world, and the smells that they concoct serve all manner of purposes, bewitching and repulsing depending on their interests. In spring, we humans glory in the floral scents of blossoming trees and flowers, but we are just the lucky bystanders, not the intended recipients of these olfactory promises of nectar. Many an insect and plant evolved a monogamous symbiosis, and the scent of a blossom is often thus meant for a specific pollinator, chemically calling to it with the aromatic vibrancy of a light house.

Not all plants are seeking to lure, but rather rebuff. Our plant culinary heroes, like rosemary and thyme, developed their smell to deter critters from choosing their leaves as lunch. Our unintended enjoyment of these plants’ pungent odors has ensured them a haven in gardens the world over, so this unexpected twist of fate should cause them no begrudging feelings. Without the accompaniment of these and other odors, our enjoyment of food would be pathetically diminished:

“We taste only four flavors: sweet, sour, salt, and bitter. That means that everything else we call ‘flavor’ is really ‘odor.’ If we have a mouthful of something delicious that we want to savor and contemplate, we exhale; this drives the air in our mouths across our olfactory receptors, so we can smell it better.” Ackerman

Woman gathering sage, from the 14th century herbal manuscript Theatrum of Casanatense.

Gathering sage, from the 14th century herbal manuscript Theatrum of Casanatense.

Our sense of smell is primal and more than any other sensory phenomena it connects us to our own lived past, to those elusive memories that rise like phantoms from the inner ether:

“When the olfactory bulb detects something—during eating, sex, an emotional encounter, a stroll through the park—it signals the cerebral cortex and sends a message straight into the limbic system, a mysterious, ancient, and intensely emotional section of our brain in which we feel, lust, and invent. Unlike the other senses, smell needs no interpreter. The effect is immediate and undiluted by language, thought, or translation. A smell can be overwhelmingly nostalgic because it triggers powerful images and emotions before we have time to edit them.” Ackerman

Aromas trigger memories with the speed of a sharpshooter, hitting us in our soft emotional limbic minds before the more cognitive and protective parts of the brain even register a change. Sight, hearing, and touch trigger memories as well of course, but these sensory inputs undergo a far longer route hindered with check points. When an odor associated with a memory is inhaled, we discover viscerally that smell alone has the power to evoke the precise emotional experiences of our past. Such overwhelming waves of sweetness, terror, grief, and joy can burst into our consciousness from just one whiff, and we forget, for a moment, that any time has passed at all.

The Soul of the Rose. J.W. Waterhouse, 1908.

The Soul of the Rose, J.W. Waterhouse, 1908.

“But when from a long-distant past nothing subsists, after the people are dead, after the things are broken and scattered, taste and smell alone, more fragile but more enduring, more unsubstantial, more persistent, more faithful, remain poised a long time, like souls, remembering, waiting, hoping, amid the ruins of all the rest; and bear unflinchingly, in the tiny and almost impalpable drop of their essence, the vast structure of recollection.”  Marcel Proust, Swann’s Way

In those days of yore, before the expansion of industry, the scent molecules of flowers would travel around 1,200 meters from their place of origin. Today, with the level of air pollution common to urban areas, these same molecules hardly make it 200 meters. It’s more essential than ever that we stop and smell the roses, otherwise we likely won’t smell them at all. So, I take time now to stick my nose right into the trumpets of daffodils and the branches heavy with blossoms, ever hopeful that I’m creating new powerful memories of scent, a trail of heavenly odors through my own past that one day I may, with luck, walk again.

The following books informed this post:
A Natural History of the Senses, Diane Ackerman
Air: The Restless Shaper of the World, William Bryant Logan

Just one person out of 7 billion + on a journey to live a life that is vibrant, soul-fulfilling, useful to others, and consciously engaged with the ecological community that sustains all life, including mine and yours.