So it’s certainly true: Evolutionarily speaking, men may be less picky about a partner than women. But Mars and Venus can each still value kissing. What’s more, members of both sexes can get better at it, whatever their goals—and both have strong motivations to so do. The sexes may view the kiss differently, but in the end, let’s not forget: The kiss also brings them together.
The Coolidge Effect
As we’ve seen in chapter 5, dopamine spikes due to novel experiences. This is likely involved in the phenomenon known as the “Coolidge effect”: the scientific name for the decline of sexual attraction in relationships over time.
The Coolidge effect gets its name from a memorable anecdote that supposedly took place during Calvin Coolidge’s presidency (1923–29). As the story goes, First Lady Grace Coolidge entered a government farm’s chicken coop while a rooster was mounting a hen. She was told the cock copulated dozens of times a day, and reportedly responded, “Go tell that to the president.” When her husband was informed of the bird’s sexual exploits, he asked whether each rooster routinely serviced the same hen. Upon learning there are many females for each rooster, it’s said that the president replied, “Tell that to Mrs. Coolidge.”
CHAPTER 7
Scent of a Man
In the 1985 film Back to the Future, Marty McFly travels thirty years into the past and encounters his parents as teenagers. After mistakenly thwarting the moment when they are first supposed to meet, he is horrified to find that his mother, Lorraine, falls for him instead of his dad. So Marty plots a convoluted scheme to reunite them by taking Lorraine to the high school dance, but as they sit parked in a car she instead grabs him, her son, for a kiss. Fortunately, in that moment Lorraine’s romantic feelings for Marty instantly change. “This is all wrong,” she says. “I don’t know what it is, but when I’m kissing you, it’s like I’m kissing my brother.”
Offscreen as well as on, it’s not at all uncommon to kiss someone seemingly perfect, only to discover you’re no longer interested in romance once your lips meet. Up until then, the stars seemed perfectly aligned for embarking on a great relationship, but afterward you instinctively sense something’s not right. The first kiss is a necessary risk in every budding sexual relationship; a recent psychology study found that 59 percent of men and 66 percent of women reported breaking things off with a prospective partner because of it.
How can a seemingly simple exchange trigger such a dramatic reversal? As it turns out, our sense of smell may be responsible, along with some very important genes and, perhaps most controversially, chemical messengers called pheromones. When it comes to deciding whether to pursue relationships in the earliest stages, your nose could serve as the ultimate mood killer.
Smell is a form of what scientists call “chemoreception”—a natural way to recognize chemical information from our environment so as to learn more about particular situations. For a long time, science sold this sense short, assuming that people had relatively poor olfactory abilities compared to other animals. The evidence from human evolution seemed to support the assumption: Standing upright moved our ancestors’ noses away from the aromatic ground, and we accordingly developed smaller “snouts” than other species of primates. Geneticists have also determined that, compared with our nonhuman ancestors, we have fewer genes devoted to detecting scent.
But that doesn’t mean our sense of smell should be overlooked. In 2004, Yale neuroscientist Gordon Shepherd surveyed the research on human olfaction and concluded that it is probably more important than usually acknowledged. Indeed, Shepherd reported, our nasal cavities, brains, and language abilities allow us to analyze smell in a more comprehensive way than other animals do.
Not surprisingly, odor plays a key role when we are sharing close quarters with another person. Ancient Roman poets, for example, described kisses that smelled of fresh flowers and incense. While this surely indulges in a bit of artistic license, there’s no doubt that a person’s odor can have a strong effect upon those they encounter, working either as an attractant or a repellant.
When it comes to kissing, factors like poor hygiene and bad breath can certainly spoil a promising moment, but it’s often our body’s natural scent that makes the most powerful impression. All over the world, people describe the smells of their lovers, spouses, children, and friends as pleasant, while they often remember the odors of strangers in the opposite way. How could this be? To understand what’s going on, we need to explore the body’s top sources of natural scent, known as the sebaceous and apocrine glands.
Sebaceous glands are found in the skin throughout our bodies, but are most highly concentrated around the nose and on our necks and faces. These glands secrete an oily substance called sebum, which contains our unique scent. When we reach puberty, the flow of sebum increases and our personal odor becomes more pronounced. Humans are very sensitive to this musk, and perhaps never more so than when kissing, with our noses often directly pressed against another’s skin.
High concentrations of an individual’s scent are also released through the apocrine glands, which can be found at the intersection of the skin and the fat stored just below. They occur throughout the body, but are heavily concentrated in the armpits and genital region where hair tufts grow, serving as a kind of scent trap. These glands also become more pronounced during puberty and release small secretions, which then dissolve into our sweat and spread. As the solution mixes with bacteria it becomes pungent, leading scientists to dub the entire underarm region the “axillary scent organ.” Interestingly, people from some regions, such as East Asia, often have fewer apocrine glands than those from others, like Europe and Africa.
The axillary organ is unique to humans and other apes, suggesting it evolved relatively recently. Anthropologists have long assumed it plays a strong role in producing an enticing scent to allure members of the opposite gender. Granted, what was enticing many thousands of years ago is not necessarily so today—but there’s much evidence from more recent history about the power of axillary scents and their role in relationships and sex.
In 1840, the English physician Thomas Laycock called the axillary odor “musky… certainly the sexual odour of man.” By the early 1900s scientists were describing the odors emanating from both sexes as attractants. In 1975, psychologist Benjamin Brody reported a practice in rural Austria in which girls would dance with an apple slice in their armpits and afterward would give it to the most worthy gentleman. In turn, he would politely, perhaps even gladly, gobble it up. It’s an unusual means of courtship, but if our body secretions are as powerful as science suggests, it was probably an effective custom.
In 1977 Austrian ethologist Irenäus Eibl-Eibesfeldt described a kind of ceremonial farewell among members of the Gidjingali tribe in Australia. A man would wipe his hands through his own underarms and then those of his departing friend. Next he would touch each of their chests. Although this sounds strange to us, it demonstrates the way that body odors have played an important role in maintaining human social bonds around the world.
Apocrine glands are larger in men, and each sex harbors a different bacterial community, giving men and women distinct scents. While the genital region seems an obvious place for the location of these glands, scientists aren’t sure about why they also exist in our underarms. Zoologist Desmond Morris memorably suggested that the axillary scent may serve to stimulate a partner during face-to-face sex, when each participant’s head is in close quarters with the other’s armpits—but that has yet to be supported by research.
Still, there are reasons to think the smells emitted by the apocrine and sebaceous glands may have the power to start or end a relationship. A central role in the process could hinge on the first kiss, which brings two people into their closest proximity yet and so serves as a kind of preliminary evaluation—and sometimes even involves swapping some sebum along with our saliva.
BUT IT’S NOT JUST our conscious reaction to another person’s smell that counts. Olfaction may also help us, on
an unconscious level, to evaluate our genetic compatibility with a potential sexual partner.
For a long time, scientists have known that humans display our genetic fitness to the opposite sex through certain physical attributes. For example, many studies have shown that we’re most attracted to people with very symmetrical facial features, subconsciously recognizing these to be an indicator of health and “good” genes. Similarly, a square jaw is considered “manly” because it’s a visible display of testosterone, while a narrow waist and wide hips in women signify reproductive capacity. In these examples, physical traits have become valued or associated with “beauty” in some cultures because they are able to provide information about the status of another person’s health, age, and fertility.
But there is probably far more to the subconscious evaluation of a partner’s genetic fitness than what we see. Sight is only one out of five senses, after all. Much research suggests that smell also helps us detect suitable partners, in a sense allowing us to sniff their very genes.
One of the most heavily discussed topics in human mate selection is the major histocompatibility complex (MHC), a group of genes that control how our immune system defends itself against disease. The MHC genes contain the DNA recipe for a certain set of proteins located on the outer surfaces of our cells, whose job is to tell the difference between cells from the body’s home team and bacteria, viruses, or fungi. When a person carries more variation in MHC genes, his or her body has an easier time recognizing these foreign invaders.
MHC diversity is also very important for producing offspring with flexible and versatile immune systems. Children benefit most when they have distinct MHC genetic material from their parents. This makes detecting MHC variation in a partner very important for the health and survival of the next generation.
But how do we identify potential romantic partners with a distinctly different MHC? We certainly aren’t sequencing their DNA. Rather, the most powerful signals may be conveyed through their natural scent.
Consider the famous 1995 “sweaty T-shirt experiment,” in which Swiss zoologist Claus Wedekind studied women’s sensitivities to male odors. He selected forty-nine women and forty-four men after testing their DNA to determine each person’s MHC type. The men wore clean T-shirts without deodorant for two nights and then returned them to Wedekind. Next, his team placed each shirt in a box with a smelling hole. The women sampled the odor of seven boxes and described each based on its pleasantness, sexiness, and odorous intensity.
The results were striking: Women nearly always preferred the scents of T-shirts worn by men with MHC genes different from their own—suggesting that we can determine our genetic compatibility with potential partners simply by following our noses. This may be particularly the case for women, who have more powerful senses of smell and taste than men, additionally heightened during peak fertility.
Many subsequent studies have been conducted since the original “sweaty T-shirt experiment,” yielding similar results. In this additional research, test subjects have also been found to rank the clothes worn by their partners and children as the most pleasant-smelling. One particularly intriguing result came from a 2006 study conducted at the University of New Mexico, which considered the MHC genes and bedroom behavior of forty-eight couples. The researchers found that the women who were more genetically distinct from their partners reported a higher degree of sexual satisfaction. Those with similar MHC genes, by contrast, reported having more fantasies about other men, and were also more likely to cheat.
Scientists have since published many articles suggesting that the odors we tend to favor emanate from those with very different immune systems from our own. However, there’s one big and notable exception: Women on the birth control pill display the opposite response. Rather than feeling most attracted to the scent of genetically distinct men, they are more likely to prefer those with very similar MHC genes to their own.
Scientists are not entirely sure why this effect occurs, but one interesting (though highly speculative) theory suggests it may have to do with the way the pill works. Birth control hormones typically fool a woman’s body into thinking that she is pregnant. An expectant mother would no longer need to seek a suitable genetic partner after fertilization has taken place. Instead, it would normally be in her best interest to stay close to her own family and those who are most likely to take care of her and her children. That means parents, siblings, and cousins—those who probably have the most similar genes, and scents—could have the most appealing odors to her during pregnancy. Thus it’s possible that women using birth control might be most attracted to the scents of men who are less than ideal genetic matches when it comes to reproduction.
If true, it’s possible that going on or off the pill during a relationship may alter a woman’s perceived level of attraction to the person she is with. It has even been suggested that this transition could be related to divorce rates in young couples. When a woman goes off the pill when she and her husband want to have a baby, their romantic chemistry may suffer, straining the relationship.
However, while this is an intriguing possibility, it’s unclear how significant the MHC is when women choose a partner. Furthermore, many complex factors besides genetics are at work keeping successful couples together or pushing unsuccessful ones apart. At present, the relationship between MHC genes and sexual attraction continues to be explored and debated. For instance, some research suggests that there is an MHC-related odor preference in both sexes, while other studies find that it mainly affects women. So while there seems to be some type of correlation between our immunity genes and our preferences in choosing a partner, science probably should not oversell it, especially when so little of the human genome is understood.
One geneticist I interviewed put it like this: Looking for the key to human relationship chemistry in a single region of our vast genome, like the MHC, is somewhat analogous to a drunk searching for his car keys under a streetlight. If we’re expecting to find answers in one particular spot of the genetic code, perhaps that’s just because it’s one of the few illuminated areas where we know to look.
Still, there’s probably something in the poet William Cowper’s remark that “Variety’s the very spice of life, that gives it all its flavor.” In genetic terms, detecting such variety requires very close proximity to a partner—a crossing of the social and cultural boundaries that delineate “personal space.” A kiss is one of the few ways to bridge that gap in a mutually acceptable, nonthreatening way. In this manner, kissing may serve as our genetic guide.
• • •
AND THERE’S AN EVEN more scientifically controversial theory about the way in which our bodies could be picking up information about the suitability of our partners. In 1959, German biochemist Peter Karlson and Swiss entomologist Martin Lüscher introduced science to the term “pheromone,” which means “carrier of excitement” in Greek. Karlson and Lüscher used the word to describe a substance released by an animal in order to trigger a behavioral or developmental reaction in another individual of the same species. While this definition works very well for insects like moths and termites—known to depend on pheromones for attracting mates, locating food, and signaling alarm—understanding its applicability is far more complex in vertebrates like ourselves.
Take laboratory mice, for example. We know they have an ability to detect pheromones, and that they release many of them in their urine. Nevertheless, scientists have struggled to determine which components of this mixture are responsible for a particular behavior in another mouse. A mouse’s urine concoction contains hundreds of different organic compounds, and an individual’s response to them might be influenced by many factors outside of chemistry, such as fear or curiosity. So even when we know pheromones are at work, it can be challenging to weed out a causal relationship between a particular chemical and a specific behavioral response.
In other cases, though, it’s much easier to catch pheromones in action. Take pigs, which have a vome
ronasal organ (VNO) located between their nose and mouth that senses these odorless chemicals. Male pigs produce a chemical called androstenone in their saliva, and when females of the species detect it, they go into a rigid stance and prepare to be mounted—a pretty clear-cut cause-and-effect example of pheromones at work. In fact, androstenone elicits such a powerful response that pig farmers use a commercially produced version to determine when sows are ready for insemination.
While many men would surely love to carry a version of that pheromone around in a bottle—and indeed, several perfume companies claim to have one on sale—scientists say we’re not there yet. In fact, the experts cannot even decide whether humans have the ability to detect pheromones at all. At least for the present, the evidence on the subject is spotty and controversial—but some of it is pretty intriguing as well.
Consider, for instance, the tendency for women who spend a lot of time together to develop synchronized menstrual cycles. It’s not folklore, there have been many scientific investigations on the matter. In 1971, psychologist Martha McClintock performed the first such research at Wellesley College, interviewing 137 women living in an all-female dormitory. McClintock recorded data about the date of onset for each woman’s period and then compared it to those of her roommates and friends. Her results, published in the journal Nature, showed that the time between menstrual onset decreased for women who spent the most time together. Because of this work, menstrual synchrony is now also known as the “McClintock effect.”
Since then, much additional research has examined how women may influence one another’s menstrual cycles, and some even debate whether such synchronization happens at all. Still, I expect that many women reading this have probably witnessed the McClintock effect firsthand, and a good deal of research published since the Nature article first appeared supports the original findings. While scientists do not know exactly why the effect happens, pheromones are the most common guess.
The Science of Kissing: What Our Lips Are Telling Us Page 8