Menstrual Synchrony or Menstrual Overlap: What Difference Does It Make?


This past summer, my sister-in-law obtained for me a copy of Professor Beverly I. Strassmann's "Menstrual synchrony pheromones: cause for doubt?" (Human Reproduction, vol 14. no. 3, pp. 579-580, 1999).

I had originally requested my sister-in-law's aid in obtaining several of Strassmann's papers, as Elsimar Coutinho, author of the book "Is Menstruation Obsolete?" had drawn upon Strassmann's anthropological work in shaping his own arguments for menstrual suppression, arguments I wished to rebut.

It turns out that Strassmann and other researchers have been unable to reproduce the findings of Martha McClintock's 1971 study, "Menstrual Synchrony and Suppression" (Nature, vol. 392, pp. 177-179, 1971).

McClintock had found: "There was a significant increase in synchronization (that is, a decrease in the difference between [menstrual] onset dates) among room mates, among closest friends, and among room mates and closest friends combined."

Strassmann, however, found that among Dogon women in Mali, West Africa: "...the [menstrual] onsets for different women were independent of each other...regardless of whether the women...were co-wives, friends, or members of the same family, lineage or village (Strassmann 1990, 1997)."

Strassmann also observed: "...Wilson (1991, 1992) noted three statistical errors in the evidence for menstrual synchrony: (i) failure to control adequately for the convergence of onsets by chance; (ii) inflation of the initial difference in onsets resulting in the spurious conclusion of synchronization over time; and (iii) sampling biases. Studies that correct for these statistical errors have found no evidence for synchronization, even as a weak effect (Jarret, 1984; Wilson et al., 1991; Trevathan et al., 1993)."

What does this all mean? For me, it meant going back and rethinking my May 1999 query letter to Rolling Stone magazine. In this letter, I'd suggested a scenario in which the all-male Beatles were actually an all-female band, consisting of "Jane, Paula, Georgia and Ringa." Based on Stern and McClintock's "Regulation of ovulation by human pheremones" (Nature, vol. 392, pp. 177-179, 12 March 1998), I further suggested that if these female Beatles had been menstrually synchronized, the album known today as Sergeant Pepper's Lonely Hearts Club Band might instead be known as Aunt Ruby's Bleeding Hearts Club Band.

And this, in turn, might have led to a very different gender balance in the music industry today.

But apparently, there is the possibility menstrual synchrony is mere "statistical artifact." Does this negate the point I'd tried to make with my female Beatles scenario?

After some consideration I decided that, regardless of menstrual synchrony's statistical significance, menstrual overlap most certainly is significant, as Strassmann herself alludes to: "Given a cycle length of 28 days (not a rule--but an example), the maximum that two women can be out of phase is 14 days. On average, the onsets will be 7 days apart. Fully half the time they should be even closer (Wilson 1992; Strassmann 1997). Given that menstruation often lasts 5 days, it is not surprising that friends commonly experience overlapping menses..."

Behind my query letter to Rolling Stone magazine lay the desire to explore the creative potential of menstruation, not only for female bandmates, but also for female producers, arrangers, composers and lyricists; and by extension, all female artists: writers, filmmakers, painters, dancers, and so on. (Which is not to say menstruation can't also be a fruitful subject matter for the male artist as well!)

Coming at it from a slightly different angle, I would hazard a guess that in Dogon society, which practices female circumcision on girls between the ages of 3-5, enforces the use of menstrual huts, and in which "co-wives" is a meaningful social category, "female bandmates" as social category is simply inconceivable.

Unfortunately, "female bandmates" as social category seems to be just about as inconceivable in "modern Western" society as in Dogon, given the relative infrequency with which young women form bands, compared to young men.

What's your opinion? Email us and let us know! We'd especially like to hear from those of you with a scientific background, qualified to evaluate the contradictory studies.




But perhaps the past, whether ancient or just 30 years ago, is not the place to be looking for menstrual synchrony.  Click here to read an email from a student at Drexel University who suggests exogenous hormones may play a role in menstrual synchrony in modern populations.

X Blood, Bread...Oranges and Apples?

X Menstrual Synchrony Index

X Return to MoltXibits

X Return to Main Page

X Contact MOLT