Pheromones and Female Leadership
Intra-species communication is ubiquitous and continuous among animals. While much of this communication can be witnessed, easily seen and heard, other forms are less overt and identifiable by the human eye or ear, for example. Pheromones are one example of such discrete forms of communication. Pheromones are chemical substances released by one animal that trigger hard-wired behaviors in other members of the same species. While the most abundant research has been done on the role of these subliminal signals among non-primate species, there have been some studies focusing on humans. Overall, such research has revealed that the potential exists for pheromones to strongly affect human behavior and desire specifically that involving sexual attraction. I, however, am most interested in the way that pheromones affect female-female interactions. I begin by examining female menstrual synchronization and go on to propose a possible link between fertility and leadership.
In most animal species, pheromone detection depends on the vomeronasal organ (VMO), a pair of mini-nostrils within the nasal cavity which perceive airborne pheromones and convey messages to the brain. Although the VMO is present in humans, it is unclear whether we posses the neuronal links necessary for pheromone information to be relayed to the brain. In other words, the debate continues as to whether in humans, the VMO is, like the appendix, a vestigial organ. Nonetheless, studies of human behavior indicate that pheromones are a real and pervasive form of communication between people. Apocrine glands, located in the underarm and pubic regions, are the main producers of pheromones. These glands develop in the embryo but become functional with the onset of puberty. (1, 2)
Martha McClintock’s 1971 study on female menstrual synchronization encouraged scientists to revisit the long-dismissed possibility of human pheromones. McClintock found that the menstrual cycles of women living together in a ventilated building, such as a college dormitory, gradually come to synchronize so that all women are on a single cycle, ovulating and menstruating in tandem. This initial study led McClintock to propose the possible existence of human pheromones. It was not until 1998 that she found evidence to support the idea that a chemical compound perceived through the olfactory system could account for the menstrual synchronization, now referred to as the “McClintock Effect,” that she saw twenty-seven years earlier. McClintock’s study involved placing odorless samples of other women’s sweat on the upper lip of female test subjects. She observed that the test subjects’ cycles either shortened or lengthened, depending on the donor’s cycle stage, in response to the exposure. Her study revealed that human axillary compounds regulate the biological rhythms of other humans. Still, scientists remained skeptical, criticizing McClintock for not isolating the specific chemical or pathway responsible for such an effect. (1)
Having spent the last four years in a female dormitory, I have personally witnessed the McClintock Effect. Still, it is unclear to me whether such synchrony is due to the averaging of disparate cycles (two cycles meeting in the middle), symmetric synchronization, or the conforming of one woman’s cycle to another, asymmetric synchronization. The latter situation requires a cycle-leader, i.e. a woman who sets the rhythm that the others will adopt. The question naturally arises as to what allows for such physiological leadership. Perhaps there is variation in pheromone strength and abundance, allowing some women to emit more powerful signals. (NB: I have not found any research definitively revealing whether pheromones are emitted continuously or in spurts and whether an individual’s pheromone production is constant throughout her post-pubescent life.) Maybe the brain only responds to the most salient pheromone and ignores the more subtle ones. Let’s say there’s a group of five women and that pheromone potency could be measured on a scale of one to five, five being the most intense. Odds are that at least one of these women is a five. If my hypothesis is correct, then the pheromones released by the women in the one to four range are ignored, becoming background odor not so different from white noise. As a result, the four other women would synchronize with number five’s cycle. On the other hand, I wonder if the cycle of a level four woman, though unable to influence the cycle of others, might be strong enough to avoid synchronization.
Perhaps the more interesting question is whether being a cycle-leader correlates with having other physical and even social attributes. For example, given that some women are more fertile than others, it seems reasonable to wonder whether these more fertile individuals are also the cycle-leaders. It hardly seems farfetched to think that fertility correlates with cycle strength which is governed by hormone production. Gynecologists often prescribe hormone supplements or oral contraceptives (pills containing a combination of estrogen and progesterone among other things) to women with hormone imbalances. Without these pills, such women menstruate extremely irregularly or not at all and are often unable to get pregnant, since amenorrhea typically correlates with a lack of ovulation, without which there is no egg to be fertilized. (It is rare but not impossible for a non-menstruating woman of fertile age to become pregnant.) If more regular and abundant hormone production causes a stronger cycle and increased fertility, then maybe cycle-leaders are the more fertile women.
In some cultures, both past and present, wealth and status are measured by number of offspring; the greater the number of children, the higher the social rank of the individual. While this manner of establishing social hierarchy may seem absurd in today’s society in which smaller families are largely the desired norm, it is not so outlandish. From an evolutionary standpoint, a human’s top priority should be reproduction in order to ensure the preservation of its genes in the population. Based on this rubric, the most fertile women are the most “successful” and deserve a higher status like that of leader.
Therefore, my next question is whether menstrual leaders, seemingly the most fertile women, are social leaders. In other words, women who elicit physiological dominance may also elicit social dominance. To put this question in the context of my earlier example, might “Woman Number Five” also be the group’s alpha-female, causing the other members to synchronize with her in ways other than menstrual cycle. Perhaps the other women mimic her style of dress and physical mannerisms, allow her to have the last word in every decision, or look to her for direction and motivation. In every social clique of which I have been a member, there has been at least one individual who sets the tone for the rest of the group. The degree of consciousness with which this leadership is acknowledged can vary greatly.
Social psychologists have studied leadership extensively, yet there still does not seem to be a conclusive answer as to why some people are better leaders than others or what it means to be a “natural leader,” if such even exists. Perhaps leadership among women could be partially explained by the existence of an alpha-female hormone. When this hypothetical compound is received and processed by other women, it becomes a nervous system input, the output of which is behavior demonstrating some sort of passivity or subordinance. On the other hand, it is also possible that a cycle-leader’s awareness, both conscious and unconscious, of her physiological dominance empowers her to act assertively. A final possibility is that leadership relates to hormone levels, and that higher hormone levels cause menstrual cycle-leadership and affect the brain in a manner that leads to a pattern of leadership behaviors.
If the cycle-leader phenomenon is real, it would be interesting to know whether it is genetically based and, if so, inheritable. For example, is a woman more likely to be a cycle-leader if her mother is? Given that fertility is often said to be heritable, it might make sense that cycle-leadership, which I hypothesize as being linked, like fertility, to hormone production, is as well. This idea of heritability sheds new light on families that are jokingly said to breed leaders. I also wonder how the cycle-leader phenomenon would apply to mothers and daughters. Would both of them have the same leadership status and therefore not produce any synching? Would the daughter be the leader because she is younger and more fertile?
This past February, a study was published in The Journal of Personality that demonstrates the reverse of what I propose: adolescents with leadership personalities show increased fertility in adulthood. The study associates leadership with status achievement, postulating that increased fertility is a means of selecting for the most successful members of the population. This finding is particularly interesting, given that socioeconomic status, the most overt measure of success in today’s society, is not associated with increased fertility. One apparent limitation of this study is the conception of “fertility,” which is simply based on the number of offspring. In contrast, I understand fertility to be a woman’s physical capacity, not mental desire, to produce children. For example, women with only one child may be highly fertile but simply opt to have a small family; Jokela et al, on the other hand, would classify such women as having a low level of fertility. What seems most likely is what the researchers propose at the end of their study: individuals who enjoy working with and leading others may be more inclined to have a higher number of offspring. (3)
In order to determine whether the thoughts presented here have any merit, much research needs to be done on the menstrual cycles, hormone levels, fertility, and social leadership of women. It would make sense to begin by establishing the existence of a menstrual leader and asymmetric synchronization. Next, scientists should investigate the other physiological qualities of these leaders, such as hormone levels and fertility. Then, it would be useful to examine female social cliques to see whether there are any parallels between menstrual and social behavior. Finally, it seems worthwhile to examine mothers and daughters and whether cycle-leadership may have some effect on what is known to be one of the most emotionally tenuous relationships.
1) Williams, Caroline. 2008 December 6. Are we wafting secret messages at each other from our armpits? Caroline Williams investigates. New Scientist. Accessed 2009 March 4.
2) Grammer, K, Fink B, Neave N. 2004 August 19. Human pheromones and sexual attraction. European Journal of Obstetrics and Gynecology and Reproductive Biology; 118 (2005): 135-142.
3) Jokela, M, Keltikangas-Jarvinen L. 2009 February. Adolescent leadership and adulthood fertility: revisiting the “Central theoretical problem of human sociobiology.” Journal of personality; 77 (1): 213-229.
Other Useful Sources
Benton, R, Asahina K. 2007 May 25. Smell and taste on a high. EMBO reports; 8 (7): 634-638.
Berglund, H, Lindstrom P, Savic I. 2006 May 23. Brain response to putative pheromones in lesbian women. PNAS; 103 (21): 8269-8274.
Martins, Y, Preti G, Crabtree C, Runyan T, Vainiu A, Wysocki C. 2005. Preference for human body odors is influenced by gender and sexual orientation. Psychological Science; 16 (9): 694-701.
Wade, N. 2005 May 10. For gay men, different scent of attraction. The New York Times. Available at: www.nytimes.com Accessed: 2009 March 4.