Remembering Smell (14 page)

I'll discuss in more detail how smell helped form the biological underpinnings of gender behavior and sexual attraction in the next chapter. This one ends with a caveat.

I confess that I grew up Catholic. Confessing is practically hard-wired in people like me. Sex is not. I was an
extreme
Catholic. I attended mass daily, prayed myself to sleep at night, kept a candlelit shrine to Saint Dominic Savio in my closet, knew the catechism by heart, and took quite literally those subliminal warnings (conveyed through the use of pictures showing souls in various shades of black) that the soul actually
did
darken (and Jesus wept) in response to my moral depravity. Never mind the physical act of sex. It was the thinking about it that was so pernicious—and of course unavoidable. I was doomed.

Enjoyment of life's sensual pleasures still doesn't come easily to me. True, a garden is the ultimate self-indulgence, rich in sensory delights. But my addiction is redeemed (in my mind) by muscle tears, thorn pricks, skin lacerations, and sweat. As to sex, I'd rather talk about it, parse it, analyze it, and deconstruct it than do it. For me, one of smell's best features had been that it caught me unaware, putting me in a romantic (i.e., receptive) mood in the bedroom. Cam's after-shave, a product called Eau Sauvage that his French brother-in-law had turned him on to decades ago, always used to have that effect on me. And what better than smell to subtly alter whatever mood my reading had put me in and send me unthinkingly over to Cam's side of the bed? The scent of his skin and hair—rosemary and Dial soap, the manlier fragrance of Barbasol Beard Buster shaving cream, and, later, the new after-shave he switched to after Eau Sauvage was discontinued in the States—used to beckon me there without my even knowing it. Simply put, body odor and musky scents signal sex, while flowers and perfumes and the smell of a person's sweater spell romance.

When I lost my sense of smell, all those sensory cues vanished. Deprived of my husband's familiar (and to me extremely attractive) scent, I sometimes forgot he was in bed beside me.

H
OW COULD VERDI'S
tragic heroine have been fooled by a fragrance? Quite easily, in fact. Many biologists who study the brain are becoming convinced that pheromones are processed in the human olfactory system even though they don't necessarily have smells. Classified as ecto-hormones (
ecto
means "external" in Latin), pheromones are secreted and convey biological messages between individuals of the same species. These signals can affect both hormone levels and behavior. Just as a hawk can't interpret the unflattering things being said about it by the squirrel cowering in its shadow, the pheromone signals that lure a male pig to a fertile female pig don't have any effect on, say, monkeys. That's a good thing for both species, biologically speaking.

The term blends the Greek words
pherein
(to transport) and
hormon
(to stimulate). It was dreamed up in 1959 to denote the chemical released by female silkworms to attract males. Discovery soon led to invention: bombykol, a commercially produced version of the silkworm pheromone, works the way all pheromones do, and farmers used it to lure problem insects to deadly traps. Tiny amounts did the trick. Bombykol was safer and cheaper than spraying with the standard repertoire of chemical pesticides.

We know that insects respond to pheromones; people are another matter. But if human pheromones are delivered as smells to the olfactory cortex, which some scientists are convinced they are, fascinating possibilities open up. A woman is more likely than a man to take note of a passing scent; she engages her thinking brain in identifying and labeling it, and it's stored in her limbic system for future reference. (Men, meanwhile, are storing football scores.) Like female silkworms, female humans are the aggressors in sex, in that they wield more influence in deciding who will mate with whom. Males are less discriminating for good reason: they are less involved in the outcome of sex, children.

Girls pick up language earlier than boys do, and most women can outtalk their boyfriends or husbands handily if the measure of success is words spoken per minute. That women tend to be the talkative sex seems at first glance illogical, since language has always been indifferent, even oblivious, to smell. With females' relatively big vocabularies, shouldn't the gender at least have come up with a word for the smell of an old sock? Some scientists believe that women are more verbal than men because the part of the female brain that processes language is closer to the amygdala than the corresponding area is in the male brain. Women are also more likely to suffer from depression than men. (However, homosexual males differ from heterosexual males; their brains respond as women's do to emotional and olfactory stimuli.) Women are better at telling smells apart and labeling them. Intuition suggests that this is because of the female's primary caretaking role: Dad goes hunting while Mom stays home with the kids. Women were the earliest cooks and gardeners. Evolutionary biologists are convinced that the males of almost all species are the more flamboyantly adorned because women are the aggressors in sex, and along with the males' fancy costumes are pungent odors, though whether pheromones (if they exist) smell is unknown.

The male-female discrepancy in language, empathy, and smell IQ becomes most noticeable during puberty and keeps expanding after that. Could those adolescent hormones possibly be pheromones?

Sometimes described as compounds, sometimes as steroids, sometimes as hormones, pheromones are that mysterious something in the urine and feces that dogs use to mark their territory. They are what pig farmers use to ignite sexual passion in female hogs. In people, they are distinguished from sex hormones, such as testosterone, which turns sexual arousal on and off by its unique and extremely subtle communication skills. However, testosterone does not direct a man to a woman whose genetic makeup is sufficiently unlike his own to favor healthy offspring. Pheromones do. That is, if they actually exist.

A famous study found that a wife can almost always pick her husband's T-shirt out of a pile of men's T-shirts with her eyes closed. If a man is "the one," even the smell of motor oil on his hands can arouse romantic feelings; the same mechanism explains why the smell of methyl mercaptan, the substance added to scentless natural gas, makes people anxious. Smell skillfully weaves together the sweet fragrances of romance and the more assertive odors of the Darwinian imperative (a.k.a. lust) to create the complex tapestry of impulse and emotion called love.

This is where the discussion bogs down. No one is speculating that methyl mercaptan is a pheromone. How does one parse pheromonal cause and effect when no one is even sure that human pheromones exist or, if they do, whether smell has anything to do with their delivery? All researchers definitely know is that these chemicals control the sexual behavior of silkworm moths, whose larvae are the silkworms that turn out silk. Smell has a far subtler role in humans' sexual activity than in bugs'.

Yet even the Victorians whispered of certain olfactory aphrodisiacs, and these days pheromones are the talk of the Internet. One website hawking a product seductively named Pherlure cologne promised that armed with the cologne, the human male could, just like pheromone-producing members of the animal kingdom, "arouse the female sex glands, heighten sensual responses and awaken her appetite for sex." That products such as this may not actually contain pheromones doesn't mean they're entirely worthless. Sexy smells can be borderline repulsive, and the smell of urine, often detected in body odor, is also in musk. One man's musk is another man's urine. Literally.

Which is probably why my husband did not find me irresistible when I picked him up at the airport after I'd slept in the same clothes for three days and not bathed. Cam stuffed his bags in the trunk, slid into the passenger seat, said hi, mentioned that he was fighting off an earache, and kissed me on the cheek, explaining that whatever he had might be contagious. "I wouldn't want you to wake up one morning stone-deaf." Then he stopped in midembrace and, lifting his hand to cover his nose, said, "Man, we gotta talk. Have you showered lately?"

My immediate response was the predictable spike in blood pressure—mortification at full throttle. It was the smoking-saucepan incident all over again. Then it dawned on me that Cam had probably been dying to discuss my body odor for weeks but had held his tongue.

So why is science interested in pheromones? Legitimate fragrance manufacturers don't have squadrons of chemists hunting down the next-generation Pherlure perfume. Even if such chemicals are at work in human reproduction, odds are they operate far under the radar. Which is why biologists are interested in what they do. If pheromones do in fact arrange the best biological marriages, they could answer puzzling questions about evolution. We know that Mother Nature seems to want to pair off the fittest individuals, sometimes only for the split second it takes for one to impregnate the other, sometimes for life. The duration and quality of the male-female hookup depends of course on what's best for the next generation as a whole, not for the couple, as Leonora's plight certainly attests.

Nonetheless, there is evidence in the animal world that in individuals who mate for life, happy marriages beget healthy kids. One researcher has traced the monogamous instinct of a particular type of prairie vole to a pair of brain hormones. These hormones (or pheromones—the words are sometimes used interchangeably) show up not only in circuits of nest-building mammals but also in those of humans. They may be involved in love itself. In 2008 scientists tested the theory of this so-called monogamy gene on humans. While the results were inconclusive, a significant correlation did emerge between responses to certain pheromones and the males' marital track records.

The Wisconsin National Primate Research Center at the University of Wisconsin-Madison announced in the fall of 2008 a striking discovery involving marmosets. These small New World monkeys live in tight-knit nuclear families, a model exceedingly rare in nature. The dads actually stick around
and
pitch in with the housework. Those dads, it turns out, are given a sort of biological anti-Viagra when newborns come. This is in the form of a sniff of a chemical—call it a pheromone—the infant marmoset secretes only at this vulnerable time, when Mom could really use some help. The chemical causes the male's testosterone levels to drop off dramatically, resulting in a distinct personality change. He behaves less like Marlon Brando in
A Streetcar Named Desire
and more like Dagwood Bumstead in the
Blondie
cartoon strip.

Why do marmoset dads get this unusual postnatal shock treatment? Scientists think it's because marmoset babies are a handful. Like human babies, they are born big, weighing in at 10 percent of their adult body weight. Plus, they come in pairs. Of particular interest to the researchers is that the marmoset males studied in their natural habitat were as aggressive as usual in protecting their turf and newborns. Apparently, in emergency situations, the male receives a jolt of testosterone. Afterward, just one sniff of the newborn is all it takes to bring the level back down.

Catherine Dulac, a Harvard molecular biologist who specializes in the genetics of smell, conducted an ingenious experiment on female mice who'd just had litters of young pups. These weren't ordinary moms. Dulac had tampered with certain ion channels, blocking the pathway of a pheromone that represses male behaviors and encourages female behaviors. This pheromone kicks in at specific times, such as when a mouse mother is supposed to be paying attention to her newborns. The result of blocking the pheromone's influence? Gender-confused creatures who brazenly mounted their mates (instead of passively waiting to be mounted) and who ignored their young. The mice were physiologically unchanged—all of their sexual equipment remained female. Yet they stopped
acting
female, and even failed to deliver the licks and cuddling believed to trigger responses essential to baby-mouse development. The babies of the altered female mice failed to thrive and eventually died.

Dulac called the results "flabbergasting" and proof positive that female mice have the same neural circuitry as males. The only thing separating the women from the men in the mouse world, she concluded, was a pheromone—sent from a female's children or her mate or both—that repressed male behavior and activated female behavior. When the researchers altered a gene and blocked the effects of that pheromone, the female mouse lost her ability to be a good mom.

Apparently, human babies send pheromonal messages too. It's a well-known fact that a blindfolded mom can tell her own newborn from other babies in the nursery just by the infant's scent. Researchers have identified a patch of skin on top of a baby's head that has cells that emit this powerfully bonding one-of-a-kind odor. Babies also seem to have an uncanny ability to pick their own mothers out of a crowd.

Next questions: How is the pheromone signal processed? How does it enter the brain and what gene decodes it and where does it go? An organ that Richard Axel calls "the erotic nose"—this is the vomeronasal organ (VNO)—is widely believed to be in charge of processing pheromones in most animals. The VNO is not the same thing as the olfactory organ, though it is located in the nasal cavity and operates, Catherine Dulac suspects, in concert with the smell system. The VNO is a chemosensory organ, meaning that it detects and responds to certain chemical stimuli, such as pheromones. In Dulac's model, the vomeronasal pathway "serves as a switch that represses male behavior while promoting female behavior. While male and female bodies are strikingly different physiologically, it appears the same cannot be said for the brain."

Dulac and her colleagues have shown that the mouse olfactory epithelium and the VNO together play a critical role in signaling for sex. Their job isn't to tell male from female but to trigger sexual behaviors. Dulac's hunch is that humans are no different from rodents in this respect; the only variation is that in humans, the olfactory system alone processes such signals and does so without any connection to consciousness. Others disagree. Some scientists argue that if the VNO is the organ that handles pheromone signals, it's unlikely that humans have pheromones. Why? A human doesn't have much of a VNO. It atrophies before birth. While recent studies indicate the VNO may be operational even in its truncated form, Dulac thinks the whole issue is a red herring. So what if we don't process pheromones the way other animals do? Couldn't they be processed along the same pathway as smell?