In other words, what you want may not be entirely up to you. But what you do about it is.
WHEN IT COMES to attraction and arousal, there are two senses we obviously rely upon—sight and touch. But anyone who has buried their head in their departed lover’s pillow to inhale the scent that remains can tell you, smell plays a major role.
Rachel Herz is a psychologist and the author of Scent of Desire. In Psychology Today, her colleague, Estelle Campenni, describes telling Dr. Herz a story familiar to many women:
I knew I would marry my husband the minute I smelled him. I’ve always been into smell, but this was different; he really smelled good to me. His scent made me feel safe and at the same time turned on—and I’m talking about his real body smell, not cologne or soap. I’d never felt like that from a man’s smell before. We’ve been married for eight years now and have three kids, and his smell is always very sexy to me.
How does it work? Much of the research around smell involves a search for human pheromones. Pheromones are chemicals that trigger specific behaviors in many organisms. Scientists have established their existence in thousands of species. But whether there are any human pheromones is a matter of some controversy.
“As of now, a lot of the claims that people might be making about human pheromones are simply not true,” explained Professor Charles Wysocki, a neuroscientist from the Monell Chemical Senses Center in Philadelphia. He went on to say, “There’s no study that has yet led to the isolation of a true human pheromone. But that doesn’t mean that they can’t exist.”
What this really means is that we don’t know very much about the subject yet. “It’s like what we used to know about willow bark tea.” Explained Wysocki, “We knew it could bring down a fever and control mild pain, but we had no idea that it was because it contains salicylic acid, the basic chemical building block of aspirin.” That’s where we are with smell and human sexuality. We think it does something, but we just don’t know what.
Most likely it does a lot.
THE GRANDDADDY OF research into scent and sexual attraction is a biologist at Switzerland’s University of Lausanne named Claus Wedekind. In 1995, he gave forty-four men new T-shirts and asked them to sleep in them two nights in a row, ensuring that the shirts were steeped in their sweat and accompanying scent. He also gave them odorless soap and aftershave to ensure that nothing masked the odor of each man’s natural “perfume.” Wedekind then asked forty-nine women to smell each shirt and rate their attractiveness. Time and again, volunteers were more attracted to the smell of shirts worn by men who had immune systems that were somewhat different from their own (more on how this works in a few pages), especially a group of very important genes that make up a key part of our immune system: human leukocyte antigen system, or HLA.
HLA acts something like a programmer at the heart of our immune system; it codes for the proteins that our immune system uses to recognize and to fight outside invaders and threats. Many of the genetic variations that doctors examine to determine if a recipient will reject or accept an organ or tissue transplant involve HLA genes.
There can be millions of genetic variations in HLA gene combinations. The more relative diversity in your HLA, the more robust or flexible your immune system is, because it’s going to recognize and deal with a wider variety of potential pathogens, making you both more resistant and better equipped to overcome infectious disease. Relative diversity, because it’s possible that there are some regional specializations to HLA—specific genes to combat diseases that are specific to a given environment.
All of which means that, if you want to give your potential child the best odds for the strongest possible immune system, you need to combine your HLA system with another that’s somewhat dissimilar. Unlike many other classes of genes, HLA can be co-expressed (which means that both copies are expressed). Having many different variants of these genes may end up providing just the right combination to deal with microbial threats. Children from parents with a very similar HLA profile, like close relatives, may not provide the best genetic opportunities to fight off microbial infections.
Farmers face a similar problem. When they attempt to increase their yields by planting an entire field with genetically similar seed (called monoculture), the resulting plants are more susceptible to disease because they lack the genetic diversity to fight off a wide range of pathogens.
Students of history may recall the Irish potato famine in the mid-nineteenth century. Potatoes were the primary cash crop in Ireland at the time. Most of the plantings were of the lumper variety—a monocrop. This created a situation ripe for disease. When the entire potato crop failed as a result of a fungus plant pathogen called potato blight, or Phytophthora infestans, the economy collapsed and thousands of Irish workingmen, women, and children died of starvation. One way some farmers try to avoid making the same mistake today is to plant different varieties of the same plant. In the same way, we avoid having children with very close relatives to ensure a more dynamic reshuffling of our genes.
In fact, having a reproductive partner with very similar genes, called consanguinity, may make it even more difficult to conceive, and it is also thought to increase the risk of bearing a child with congenital diseases. The increased difficulty in conception may be an outgrowth of the same phenomenon: if highly similar genes or relatedness between partners increases the risk of birth defects, it may also increase the risk of miscarriages resulting from abnormal embryos and fetuses.
Having children with someone with a completely dissimilar HLA profile, meaning very big differences in their HLA genes, may not be the best idea either. If two people with vastly different HLA profiles have children, they might not pass on an HLA combination that evolved in response to the microbial environment they live in. This means giving up on the best chance to fight off infections and infestations that are specific to a certain geographic location. In reality, of course, it’s far more complex, but you get the idea—partners with diverse HLA are giving their potential offspring an immunological leg up, and partners whose HLA genes are too closely related may have difficulty conceiving.
Much of my own research has dealt with the relationship between certain HLA genes and resistance to infections, but, when it comes to olfaction and attraction, I’ve always wondered what it is exactly that people smell when they are sniffing out a potential partner. When I spoke with Herz, she explained how she believes that HLA manifests itself as body odor:
Your body odor, whatever it is, is reflective of your particular HLA. However you smell when you come out of the shower, before you put anything on, is a reflection [of HLA] from the point of view that the proteins that your HLA is coding for are being degraded by the bacteria that are on your skin’s surface. And the by-product of that degradation is what produces your very own body odor. And because you have different proteins expressed as a function of your HLA uniqueness, then you have a specific, distinctive body odor.
The good news about scent and sexuality is that there are always going to be people who like your particular odor. Because the attractiveness of your smell depends on the genetic makeup of the smeller, and their past exposure, and because there is so much genetic variety, your smell is bound to have many matches out there. “There’s no Brad Pitt of smell,” says Herz. “Body odor is an external manifestation of the immune system, and the smells we think are attractive come from the people who are most genetically compatible with us.”
Not only does HLA compatibility have a bearing on a couple’s suitability as potential parents; it also has implications for their suitability as potential partners for life. University of New Mexico researcher Christine Garver-Apgar studied the relationships of heterosexual couples in the context of the relative similarity or dissimilarity of their HLA patterns. The couples provided information about their relationships and sexual habits, and then matched that information against genetic testing that documented their HLA patterns. They found that the more HLA genes a couple shared, the less sexu
ally responsive the women were to their partners and the more they cheated on them. In fact, Garver-Apgar found that there was a direct correlation between the number of HLA genes a couple shared and the odds that the woman would cheat. Fifty percent HLA genes in common? Fifty percent chance the woman was fooling around. What about men, you ask? Most of the studies involving smell concentrate on women, who naturally have a much keener sense of smell than men. Women’s preferences also seem to be much more affected by smell.
But relying on sense of smell alone is not foolproof when it comes to mate selection. Earlier this year a British couple sought to have their marriage annulled after discovering they were fraternal twins. They were adopted by different families as babies and grew up without any knowledge of each other. If every nose were a genetic bloodhound sniffing out and rejecting similar genes, then your twin ought to smell like a skunk. Fortunately for family unity, it doesn’t really work that way; we tend to be comforted by the familiar smells of family, even if we want something else in a mate.
Though women are more sensitive to male smells in general, men are especially sensitive to women at a specific point in their menstrual cycles. When? When they’re ovulating, of course.
Professor Devendra Singh, of the University of Texas at Austin, conducted his own version of the T-shirt test. He gave two new T-shirts to about two dozen women. They slept in one shirt during the most fertile part of their menstrual cycles, on days 13 to 15; they slept in the second shirt on days 21 and 22 when they were no longer actively fertile. As in the Wedekind study, the women volunteers were asked to avoid perfumes, scented soaps and shampoos, and even pungent foods, like garlic. Sure enough, when men were asked to sniff the shirts and pick their preference, they picked the smells from the fertile phases over and over again.
Smell seems to affect the process of attraction in direct relation to nature’s expectations of us in the reproductive process. Since the biological cost of reproduction is so much higher for females than for males, it shouldn’t be a surprise that women may be wired to sniff out men who will provide the right traits to give them the healthiest babies. And men in turn may be wired to sniff out women who are ready to make babies.
Interestingly, the compounds that seem to exert the strongest sexual pull are gender-specific. That is, male compounds trigger a sexual response in women, and female compounds trigger one in men—with one important exception. And the exception really does seem to prove the rule.
Homosexual men have the same reaction to certain male odors that heterosexual women have, not just subjectively, but in terms of measurable brain activity.
Ivanka Savic-Berglund and a team of researchers at the Karolinska Institute in Stockholm, Sweden, used a brain-imaging technique to examine the responses of a group of straight men, a group of straight women, and a group of gay men, to two odors, one from men and one from women. The male compound was a testosterone-related chemical found in men’s sweat, and the female compound was an estrogen-related chemical found in women’s urine.
Most smells activate specific areas of the brain that are known to govern how we receive and process scents. And that’s exactly what the sweat compound did when heterosexual men smelled it—it activated the smell-related areas of the brain. Same for women and the urine compound. But when straight men were exposed to the female compound, brain imaging revealed that not the smell-related zones but the hypothalamus, which controls sexual behavior, kicked into overdrive. The same thing happened when women were exposed to the male compound. But what was especially noteworthy was the response of gay men. They responded to the male compound exactly as the straight women did. Instead of engaging the smell-related zones of the brain, the brain imaging revealed that the male sweat compound energized the hypothalamus of gay men.
Dr. Savic followed up this study in 2006 with a similar examination of twelve heterosexual women, twelve heterosexual men, and twelve homosexual women. As in the previous study, the heterosexual men processed the male odor in the normal scent regions of the brain and the female scent in the sex-related area of the hypothalamus. The heterosexual women did the opposite. In the case of the homosexual women, the male sweat-derived odor activated the olfactory centers of the brain as expected, but the female urine-derived scent activated both the sexual areas of the hypothalamus and the normal olfactory centers of the brain. The results were not quite as straightforward as with the gay men in the previous study, but the female scent did activate the sexual areas of the brains of homosexual women in a way that it did not in the heterosexual women.
Charles Wysocki, the neuroscientist from Philadelphia’s Monell Chemical Senses Center, completed a study that asked “odor evaluators” in four categories—heterosexual men, heterosexual women, homosexual men, and homosexual women—to indicate their preference among odors collected from “odor donors” in the same four categories. None of the odor evaluators were odor donors.
The researchers asked the donors to go through a “washout” phase for nine days in order to cleanse their bodies of foreign odors; they used odorless soaps and shampoos, avoided pungent foods like garlic and curry, and didn’t shave their armpits. For the next three days, they wore cotton gauze pads under their arms. The pads were then cut into pieces and combined with pads from other donors in the same category (heterosexual men or women, homosexual men or women) and put into plastic squeeze bottles. This gave the researchers a kind of hybrid odor sample for each class by reducing the impact of any individual odor.
When odor evaluators were asked to choose between different odor samples, a few clear patterns emerged. Here’s some of what the report said:
Heterosexual males, heterosexual females, and lesbians preferred odors from heterosexual males over odors from gay males; gay males preferred odors from other gay males…. Heterosexual males, heterosexual females, and lesbians over the age of 25 (but not those ages 18–25) preferred odors from lesbians over odors from gay males…. Finally, gay males preferred odors from heterosexual females over those from heterosexual males.
If evaluators were selecting odors randomly, no clear patterns among the gender and orientation groups would have emerged, of course. Clearly, some complex interaction between orientation, attraction, and odor affected the participants’ choices. By the way, if you’re wondering about the role of HLA, the genes that play a key role in our immune system, this research examined some of the broad strokes of odor and sexuality—specifically as it relates to sexual orientation. The relation of HLA, odor, and attraction seems to involve a finer filter—the genetic compatibility of potential parents, not fundamental gender attraction. But this clearly demonstrates that there is much more to smell and attraction than HLA.
What isn’t clear from any of these studies, of course, is whether the preferences participants indicated were a result of their sexual orientation or involved in determining their orientation.
“Our study can’t answer questions of cause and effect,” says Dr. Savic. “We can’t say whether the differences are because of pre-existing differences in their brains, or if past sexual experiences have conditioned their brains to respond differently.”
What is clear is this: smell is intimately involved in intimacy. The next time somebody tells you they just don’t have the right chemistry with someone, they might mean it literally, even if they don’t know it.
WHILE THE SMELLS we find sexy may be as varied as our DNA, sexy sights are another matter entirely. There actually are some pretty universal standards for what humans tend to find visually attractive, and they start with a cliché—tall, dark, and handsome.
Across cultures and continents, many women tend to be attracted to men who are relatively darker than others in their group. And there’s a perfectly good reason—they are likely to have healthier sperm.
Folic acid, or folate, is an essential nutrient found in leafy greens such as spinach; it gets its name from the Latin word for leaf, in fact. Folate is critical to the healthy production of new cells. It’
s especially important during periods of rapid cell growth, as in pregnancy, which is why many doctors advise women to take it as part of a prenatal vitamin package when they’re trying to get pregnant (even up to a year in advance), to prevent neural tube defects such as spina bifida.
A recent study published in 2008 in the journal of Human Reproduction by a team at the University of California at Berkeley, suggests that folate is important for male reproductive health as well. Men with higher levels of folate had higher percentages of healthy sperm.
In an average healthy man, up to 4 percent of the sperm in his ejaculate has the wrong number of chromosomes, called aneuploidy. High percentages of aneuploidy can impact fertility and has been linked to miscarriage, birth defects, and genetic disorders such as Down syndrome. The Berkeley study showed that men who consumed the highest levels of folate through food, vitamin supplements, or a combination of the two, had as much as 30 percent less aneuploidy in their sperm than men with the lowest levels of folate. When you consider that a normal adult male produces sperm at the astronomical rate of around 100 million per day, it makes sense that a vitamin that promotes healthy cellular reproduction would be good to have around.
But where does tall, dark, and handsome come in? Ultraviolet rays destroy folate. Darker skin is achieved by cells called melanocytes that produce different types and amounts of melanin, (naturally occurring pigments that absorb ultraviolet radiation and releases it as heat), protecting the body from its harmful effects. So the darker a man is, the more likely he is to be protected from ultraviolet rays, which means the less folate is destroyed, which means the healthier his sperm.
How Sex Works Page 8