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Gayil Nalls, Ph.D.
Gayil Nalls Ph.D.

Dating, Mating and Olfaction

Little known side effects of hormone-based birth control.

Many women find themselves in an unfortunate predicament after several years of coupling with their partners. The story often goes something like this: Countless hours spent searching for a mate finally leads to the appearance of a suitable "Mr. Right." The two decide to move in and possibly get married-all the while juggling careers, finances, family obligations, and friendships. At some point they decide that the time is right to stop using contraception in the hope of starting a family.

While still pleasurable, sex becomes predominantly functional, timed to the couple's tracking of the woman's basal body temperature and cervical mucus, for the best time to get pregnant. Intercourse without signs of ovulation become nonexistent and little attention is paid to the level of chemical attraction that brought the two of them together. Even if the couple eventually conceives, many first pregnancies result in miscarriage, an emotionally-devastating and physically stressful outcome, and one often without sufficient explanation as to why.

Flash forward to a future time when a baby is born. The couple is elated to be parents, but exhausted with doctor's visits, nighttime feedings, and round-the-clock attention devoted to the new addition, as well as maintaining a home and holding down a job. Sex may or may not be on the docket of regular activities. While the man may find some time when he is in the mood, the woman starts to sense a nagging suspicion that she may no longer be attracted to her mate. She asks herself, "Is it the breast feeding? The flux in hormones? Post-partum symptoms? What's wrong with me?"

"What's wrong with us?"

There may be several factors contributing to this all-too-common situation. Rarely considered is the genetic factor, which could explain the lack of attraction, the timing of the woman's feelings, and the miscarriages. The full story of this situation can be traced to the first moments of dating and mating.

Dating has long been associated with masquerade. It is well known that the codes and signals women employ to attract a mate - provocative dress, coy and flirtatious behavior (driven by sexual fantasy) - are deeply rooted in evolutionary biology. Often unrecognized, however, is the role that the sense of smell plays in the evolutionary system of attraction. We each produce a chemical aura as unique as our fingerprints. Starting at puberty, feasts of aromatic chemicals that make up our individual "odor-prints" communicate our sexual compatibility. This continues through our fertile lives and is perceived by others on an unconscious level.

Olfaction is the least understood of our five senses, but it is perhaps the most profound when it comes to how the human brain evolved in concert with the natural world and for the benefit of sexual reproduction. One way in which humans communicate with each other is through the senses of smell and taste. Attraction is quite literally about chemistry; our noses have receptors for scent molecules, some so fine-tuned that even consciously imperceptible chemicals are apprehended and processed by the brain on an unconscious level. The majority of the aromatic information that we receive from other humans is apprehended in this way.

Evolutionary biologists had long hypothesized that humans pick mates by smelling them, but this was only proven in 1995 by biologist Claus Wedekind in a groundbreaking initial study while at the University of Bern. In that study, women were asked to smell t-shirts worn by different men and to rate which ones were most attractive to them. The participants overwhelmingly selected the shirts worn by men whose major histocompatibility complex (MHC) differed from their own.

MHC is a large cluster of genes that relate to immune systems. Wedekind's study shows that women are innately attracted to partners who have different immune systems than their own, indicating divergent genetic profiles. From an evolutionary standpoint, the offspring of such unions are genetically more diverse, ensuring a healthy gene pool in successive generations. Evolution has thus furnished us with a built-in mechanism to guarantee the best outcome of our dating and mating, from the longevity of our attraction to our partners to the success of our childbearing.

The 1995 study also included a troubling side note: a woman's odor preference is compromised while taking oral contraception. Initially receiving criticism for its low number of participants, the 1995 findings related to the pill were upheld by a more extensive 2008 study "MHC-correlated odour preferences in humans and the use of oral contraceptives" conducted by S. Craig Roberts and The Evolutionary Psychology and Behavioural Ecology Research Group based at The University of Liverpool, UK. In short, the same pill that gave women peace of mind and the perception of control over their reproductive destinies also dismantles one of evolutionary biology's greatest gifts- the capacity to literally sniff out a suitable partner. And yet the emotional and physiological impact of this troubling side effect of hormone-based contraception has received very little attention.

The two above-cited studies, and several related studies indicate that normal hormonal mechanisms are instrumental in a woman's ability to smell a mate whose MHC cluster is different from their own. Contraceptives, such as pills, patches, or inserts, disrupt perception of MHC odor cues and cause women to chose less suitable partners. Altering the means by which women choose mates may lead to unions with weak genetic foundations, as happens with inbred offspring for example. Inexplicable miscarriages are frequently the body's next line of defense against the conception of a fetus by partners who share similar genetic profiles.

Since these kinds of contraceptives hormonally mimic pregnancy, women remain attracted to partners with similar genetic profiles after conception. However, when going off hormonal contraceptives or after a child is born, the body returns to its natural hormonal state. As a consequence, a woman's attraction to her life partner may come into question at this time.

While we have been taught that love transcends mere physical attraction, the subconscious role that olfaction plays in sustaining and supporting intimacy and love for our partners (and in fact all members of our families) is indisputable. For these reasons, the olfactory system is our inner capacity to forge strong relationships. And its not only women's mate choice preferences that are effected. Evidence shows that men are more highly attracted to ovulating women. This six day fertile phase of the natural menstrual cycle, which induces physical changes in a woman, is very detectable by men. It is also altered in women on hormone contraceptives putting them at a disadvantage in attracting a mate.

The olfactory system's subconscious guidance in our attraction to our partners helps maintain the genetic strength and adaptability of the human community. By overriding this evolutionarily-honed instinct for reproducing, we risk leaving future generations vulnerable to pathogens, with weakened adaptability to changing environmental circumstances and questionable reproductive capacity. Despite the advantages of hormone-based birth control, its use continues to come at a steep price due to the profound disadvantages it can lead to in the lives of both parents, the health and happiness of their children, and future generations.

Most scientists agree that when you manipulate a major organ system, there will most likely be adverse side effects, even if it takes years to determine what those side effects are. However since the US Food and Drug Administration (FDA) approved the pill in May of 1960 (this year marked its 50 anniversary), neither the FDA, nor the drug companies have conducted further investigations into these troubling side-effects and their long term genetic implications.

Creating public awareness and education regarding the side effects of hormone-based contraception is a crucial step. As chronicled in Elaine Tyler May's new book, "America and the Pill: A History of Promise, Peril, and Liberation," the pill has been a banner under which women could unite for the ability to choose their reproductive futures. However, now its 2010 and women are still not informed about the full range of effects of hormonal contraceptives. Controlling fertility or having the ability to determine the time of motherhood should not jeopardize the health of children, the happiness and success of families, nor the future of culture at large.

In order to address the risks of the alteration of reproductive and social behavior-such as mate-choice, relationship fulfillment, increased chance of divorce and the health of children and descendants (along with oral contraceptives associated role in breast cancer and heart disease)-the FDA, medical community, and pharmaceutical companies should unite to establish medical, ethical, and legal guidelines to ensure informed use of hormone-based birth control. As part of a woman's right to reproductive freedom, and to protect the health of future individuals, we need to understand all possible consequences related to using the pill, the patch, inserts and future forms of hormonal contraception. And most important, women and men still need to fight for a safer contraception.

But individuals can take charge now as well. If you are in love and on hormonal-based birth control, your next stop should be a geneticist, that's if you don't want to change to other forms of contraception and see if you love your mate's smell. Genetic testing and counseling for partners, including a comparison of your MHC clusters, can provide an enormous benefit to your long-term happiness and decision-making. It may also offer some explanation for a variety of concerns in your relationship.

If you are wondering how to find a genetic counselor, you can visit the website of the National Society of Genetic Counselors at and go to Resorcelink to find a listing of certified genetic counselors around the world. Also, there are dating services that analyze DNA to be sure that the immune systems of client matches are different. Boston's says it was among the first to use DNA matching to help identify compatible people.

For successful family planning, real empowerment of women, and the optimization of our species, it is imperative that we know more we know about the evolution of olfactory communication and its role in sexual selection by signaling individual identity. It is clear that despite our dating rituals we are far from just visually oriented. Olfactory cues do help us detect a suitable mate. It is not the short skirt, the highest stilettos or the celebrity branded perfume or cologne that brings Mr. Right and Ms. Right close- it's the bodily smell of the real you.

About the Author
Gayil Nalls, Ph.D.

Gayil Nalls, Ph.D., is an interdisciplinary artist based in New York.

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