Biology 202
2003 Second Web Paper
On Serendip

Our class was initially shocked to learn about proprioception, as it was difficult to grasp the concept that our bodies could possess senses about themselves and the outside world of which our I-functions are unaware. Even more disturbing was the idea that these bodily perceptions could regulate our behaviors without our conscious thought or consent. The class seemed comforted, however, when this seeming sixth sense was found to regulate many functions we consider thoughtless and ethically unimportant, such as heartbeat and balance. These choices we could leave to our bodies as long as our I-functions had power over the meaningful concerns of life.

But the mounting evidence for the existence of human pheromones throws a wrench into the mechanism of this easy solution. Pheromones, or chemical signals sent from one individual to another which affect behavior, are argued to influence meaningful behaviors once thought to be completely controlled by conscious personal choice, such as sexual willingness and attraction. They also introduce the possibility that we may be constantly communicating with each other and making interpersonal judgments of which we are unaware. The possible implications of this invisible sense are significant and far-reaching.

The first convincing evidence for the existence of human pheromones was presented in 1971 when Martha McClintock published a paper documenting the synchronization of the menstrual cycles of her and her fellow female dorm mates.(10) It seemed likely that something pheromonal was at work, as this phenomenon mirrored a similar occurrence caused by pheromones in mice, known as the Lee-Boot effect. (2) McClintock provided further evidence for this a few years ago in a controlled experiment published in the Journal Nature. (1) She found that secretions from the underarms of females in the follicular phase of menstruation significantly shortened the cycles of other female test subjects when applied under their noses, and secretions from the ovulatory cycle accordingly lengthened their cycles. In addition, she noticed that certain females seemed much more sensitive to the secretions than others, with responses of lengthening or shortening ranging from 1 to 14 days difference.

McClintock also predicts that pheromones of social interaction may be found to affect humans in many more of the same ways they have been found to affect rats, including: age of puberty onset, interbirth intervals, age at menopause, and level of chronic oestrogen exposure throughout a woman's life. (1) Not only does this evidence point toward a type of invisible chemical communication between women, but the variable sensitivities of certain women compared to others indicates that certain women may be dominant over others in determining the cycles of the entire group. Further evidence of this invisible power structure is provided by Michael Russell, who performed a case-study on a female colleague who had observed that it was always her cycle to which other females synchronized. (2)

Other studies provide evidence that it is not only females who communicate with each other pheromonally, but that males as well as females can influence each other sexually. Various studies have found that sexual exposure to males causes irregularly cycling women to begin cycling more regularly(4,2), which is another well-studied occurance in mice known as the Whitten effect, and has been linked to pheromones (2). Dr. Alex Comfort also noted that during Victorian times the average age of the onset of menstruation was much higher than in post-Victorian times, when co-education of males and females became more acceptable. (2) So male pheromones may play a large part in the regulation of the hormones which cause menstruation. Women who have sex with men at least once a week have in fact been found to have fewer infertility problems and milder menopause than those who do not. (4) And sex may not be necessary, but rather just the exposure to men's pheromones which are released only at close range. The implications of these findings are that male pheromones may be necessary for women to achieve optimimum health, and that this may in part explain the female attachment to men.

Other studies by Russell also found that around 6 weeks of age almost all babies will react more favorably to a pad containing the sweat of their mother than to a stanger's pad, and that people can identify their own sweaty shirts as well as those of a strange male and female with a relatively high rate of accuracy. (2) These functions in humans seem similar to the identifying functions of pheromones found in many other animals. (8)

But perhaps the most controversial human behavior which may be influenced by pheromones is sexual preference and mate selection. A case study by Kalogerakis found that at around the age of three years a boy named Jackie began to prefer the smells of his mother much more than those of his father, especially after she had recently had intercourse. The smells of the father at this time, until the boy reached six years old, caused aversion and some nausea. This behavior supports not only the theory of sexual attraction by pheromones but also Freud's theory of an innate "Oedipal complex" in young boys. (2) And in addition to women's health being beneficially affected over time by exposure to male pheromones, the moods of women have been shown to improve when exposed to the male steroid androstadienone. (12) A study also found men and women are more attracted to individuals whose genetically based immunity to disease is most different from their own. (5) Companies have not only begun to market so-called "pheromone colognes" containing compounds meant to attract members of the opposite sex, but these colognes have been reported to have some success for both men and women. (4,5)

There are still many who are skeptical about the actual existence of a pheromone receptor in humans which is separate from other smell receptors in the nose. The vomeronasal organ, which serves this purpose in other species, has long been thought nonexistent in humans after a certain fetal growth stage. However, there is a distinctive pit in the human nose with nerve endings which may still serve this purpose, if the axons of these neurons end in separate, more primitive parts of the brain than the more common nasal sensory neurons. This has yet to be definitively proven, but it seems especially unlikely that menstrual synchronization could be caused by scent alone and not specific chemical factors independent of the I-function.

It may not seem important that woman are unknowingly communicating and adjusting their menstrual cycles in order to achieve equilibrium with those around them, but the idea that some women may be dominant over others in this process is very interesting. What evolutionary quality do these women have, and what is its purpose? Is there an aspect to human personality and social rank which is inherent and unseen? There could in fact be many pheromonal factors working within and across the sexes all the time, influencing our preferences for social and sexual interaction. If Kalogerakis is to be believed, disturbing sexual developments such as Freud's Oedipal complex cannot simply be explained away, but are much more deeply rooted. And what might the implications for our society be with the increasing chemical complexity of the products we use, many containing animal and/or human pheromones? Although the ultimate decision of choosing a mate or selecting a friend must pass through the I-function, how do we know where our attitudes towards others come from? Could it all be more unconscious than we think?

References

1)Regulation of Ovulation by human pheromones, Stern and McClintock's publication in Nature 1998
2)Pheromones in Humans: Myth or Reality?
3) Chicago: Campus of the Big Ideas
4) Sexes: The Hidden Power of Body Odors, article from Time, 1986
5) Pheromones: Potential participants in your sex life
6) Following Your Nose to Optimal Sexual and Reproductive Health and Happiness, student webpaper 1999
7) Study finds proof that humans react to pheromones
8) Human pheromones: Communication through body odour, article in Nature 1998
9) Love Stinks: Intraspecies Chemical Communication, student webpaper 1999
10) Nailing Down Pheromones in Humans
11) Pheromones, student webpaper 1998
12) University of Chicago research points to new category of odorless chemical signals


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