Today the Talmud tells two stories of rabbis, Rav Elazar and Rava who each used their keen sense of smell to identify the origins of uterine blood.
נדה כ,ב
ואמאי קרו ליה מרא דארעא דישראל דההיא אתתא דאייתא דמא לקמיה דרבי אלעזר הוה יתיב רבי אמי קמיה ארחיה אמר לה האי דם חימוד הוא בתר דנפקה אטפל לה רבי אמי אמרה ליה בעלי היה בדרך וחמדתיו קרי עליה (תהלים כה, יד) סוד ה' ליראיו
There was an incident involving a certain woman who brought blood before Rabbi Elazar for examination, and Rabbi Ami was sitting before him.Rabbi Ami observed that Rabbi Elazar smelled the blood and said to the woman: This is blood of desire, i.e., your desire for your husband caused you to emit this blood, and it is not the blood of menstruation. After the woman left Rabbi Elazar’s presence, Rabbi Ami caught up with her and inquired into the circumstances of her case. She said to him: My husband was absent on a journey, and I desired him. Rabbi Ami read the following verse about Rabbi Elazar: “The counsel of the Lord is with those who fear Him; and His covenant, to make them know it” (Psalms 25:14), i.e., God reveals secret matters to those who fear Him.
אפרא הורמיז אמיה דשבור מלכא שדרה דמא לקמיה דרבא הוה יתיב רב עובדיה קמיה ארחיה אמר לה האי דם חימוד הוא אמרה ליה לבריה תא חזי כמה חכימי יהודאי א"ל דלמא כסומא בארובה
The Gemara further relates that Ifera Hurmiz, the mother of King Shapur, sent blood before Rava for examination, [as she sought to convert and was practicing the halakhot of menstruation]. At that time Rav Ovadya was sitting before Rava. Rav Ovadya observed that Rava smelled the blood and later said to the woman: This is blood of desire. She said to her son: Come and see how wise the Jews are, as Rava is correct. Her son said to her: Perhaps Rava was like a blind man who escapes from a chimney, [i.e., it was a lucky guess…]
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Each rabbi had inhaled the odor of the sample of blood and and concluded that it was “the blood of desire.” Rashi explains that the women from whom the sample came had sexually desired her husband to the degree that it had prompted a uterine bleed (שנתאוית לבעלה וראתה הדם מחמת תאוה). Leaving aside the question of whether menstrual bleeding and sexual desire are somehow related, the question we will focus on is this: could these blood samples really have smelled different? And that brings us to the topic of the day: pheromones.
Pheremones and Menstrual synchrony
“Pheremones are chemical signals that have evolved for communication with other members of the same species.” That is how the Oxford University zoologist Tristram Wyatt, defines them, though he is an admitted sceptic when it comes to their existence in us. The earliest claim that they might exist in humans was made back in the 1970s in those famous studies of synchronized menstruation in women who lived together in the same college dormitory.
The landmark study was published by in 1971 the American physiologist Martha McClintock, who studied the menstrual cycles of young women living on the leafy campus of Wellesley College in Massachusetts. McClintock analyzed their mensrtual diaries, and noted “a significant increase in synchronization among roommates and among close friends.” She was quick to note that although this was a preliminary study, “the evidence for synchrony and suppression of the menstrual cycle is quite strong, indicating that in humans there is some interpersonal physiological process which effects the menstrual cycle.” Just as Rava and Rav Elazar had claimed.
Lots of hypotheses were proposed to account for this menstrual synchrony. Perhaps the young women were eating similar foods, or were influenced by the same weather, or were subject to the same daily stresses of exams. Perhaps the phases of the moon were responsible? Or perhaps they were influenced by the presence of men near the campus? There was another possibility too. Perhaps there was a pheromonal signal between the menstruating women. That might be the cause. Maybe a chemical signal between the women caused the synchrony, rather than it occurring as the result of an alignment of each woman’s cycle to some external environmental signal.
Only there was a big problem. Over the decades scientists tried to replicate McClintock’s findings, but they couldn’t. Twenty years passed and four studies couldn’t replicate the findings. Thirty years passed and new experiments failed to find evidence of menstrual synchrony. And now, almost fifty years since the original study the scientific consensus is that at best there is no evidence for it; at worst, it has been thoroughly discredited. Here is how a 2014 review in the Journal of Sex Research summarised the field:
An appreciation of the likely patterns of ovarian cycling throughout much of human evolutionary history (until the 20th century) coupled with data on the extraordinary variation within and among contemporary women in cycle length quickly leads to a nagging doubt regarding the likelihood of MS sensu stricto. Add a good dose of probability theory and the fact that reasonably well designed studies have failed to support the MSH, and one is left wondering why so much attention has been given to searching for elusive mechanisms and constructing convoluted evolutionary scenarios…
So much for menstrual synchrony. But now let’s get back to the question of pheremones. Since a pheromonal mechanism of synchronization is the only plausible mechanism to account for synchrony, and since synchrony doesn’t occur, then maybe it follows that there are no pheromones that modulate the length of the human menstrual cycle. To test this, Jeffrey Schank, a psychologist from the University of California at Davis painstakingly reviewed “all the studies directly or indirectly related to pheromone modulation of the menstrual cycle,”though he noted that “this is a very small literature of eight studies spanning 25 years.” All eight studies had serious methodological flaws that you can read about here, and Schanks concluded that when taken together, “these results cast doubt on the existence of pheromones that modulate the length of menstrual cycles.”
For example, consider a study by Kathleen Stern and (you guessed it…) Martha McClintock, published in the very prestigious journal Nature in 1998. They claimed that that odourless compounds “collected from the armpits of women in the late follicular phase of their menstrual cycles accelerated the preovulatory surge of luteinizing hormone of recipient women and shortened their menstrual cycles. Axillary (underarm) compounds from the same donors which were collected later in the menstrual cycle (at ovulation) had the opposite effect: they delayed the luteinizing-hormone surge of the recipients and lengthened their menstrual cycles.” Wouldn’t that support the suggestion that humans produce compounds that regulate a specific neuroendocrine mechanism in other people without being consciously detected as odours? That is, after all, the classic definition of a pheromone.
Well no. In the first place the study results were a trend but were not statistically significant. But more importantly, Schanks noted that it was was confounded by using the third cycle, which was a treatment cycle, as a baseline cycle for determining the change in cycle length resulting from ovarian cycle secretions. It was as flawed as the other seven studies.
The search continues
We have no evidence that human pheromones exist. But that is not the same as having evidence that they do not. The search continues, and some are hopeful that by returning to good scientific principles and by using more rigorous techniques we can avoid some of the mistakes of the past.
And what are we to make of the claim that Rava and Rav Elazar could detect pheromones? Well, we should make of it exactly what the Talmud itself makes of it. Either their conclusions were the result of God’s direct revelation to “those who fear Him” (סוד ה' ליראיו), or, and this is equally possible, they were just a lucky guess. Take your pick.
“Science is not subject to statutes of limitation or prohibitions against double jeopardy. Theories, methods, and data are forever open to critical review. Science only progresses when hypotheses and theories are given the most severe tests possible. Indeed, even when a theory passes a severe test, errors may be subsequently found in data and methods supporting that theory. This implies that neither theories, data, nor methods can be accepted with absolute certainty. Scientists are fallible, and even the peer review process is no guarantee against error. The fact that errors may occur at all levels of scientific inquiry appears to lead to the skeptical view that all of science is on an equally uncertain footing. However, by repeatedly scrutinizing theories, data, and methods to weed out errors, we can have growing confidence in those that survive. This is a never ending process, but the more we critically scrutinize previous results, the more confident we can be in those theories, data, and methods in which we fail to find errors. Perhaps future studies will find indisputable evidence of pheromones that modulate menstrual cycles, but the studies to date have not. ”
