Blood, Bread...and Menstrual Synchrony?


Now we turn to a book making an even greater claim than 40 years’ worth of menstrual synchrony, and that is poet Judy Grahn’s “Blood, Bread and Roses:  How Menstruation Created the World.”  Grahn suggests the following “early human” scenario:


Acquiring an externally based mind required early humans to connect to something outside of themselves as a frame of reference, to connect physically; and this was accomplished when the females evolved a menstrual cycle capable of synchronous rhythm, or entrainment.  Entrainment is the quality of two similarly timed beats to link up and become synchronized in each other’s presence.  Nondigital clocks behave this way, and so do drums.17 This quality of interactive rhythm, being not mechanical, applies as well to the periodicity of menstruation [...]”


This unique cycle in correspondence with the cycles of an outside body, the waxing and waning of the moon far beyond the surface of the earth, taught humans to see from outside of their animal bodies, and to display that knowledge externally, in physical culture.  The menstrual mind became externalized because females were forced to teach its perspective to members of the family who did not menstruate.  Males, in learning the pattern, greatly extended it, rearranged it, demonstrated their comprehension one further step, and mirrored back to the females:  an ongoing dance of mind between the genders.  The consequences of the menstrual/lunar correspondence is what has divided us, for good and ill, from the other animals.”


-- pg 13-14, “Blood, Bread and Roses:  How Menstruation Created the World,” Judy Grahn, 1993


There is an extraordinary, and intriguing, argument being made here.  This argument starts from a certain interpretation of the behavior of “nondigital clocks…[and] drums,” which is then generalized to “the periodicity of menstruation.”  In this interpretation, the “entrainment” (i.e., synchrony) of nondigital clocks and drums is “not mechanical.”


But is that true?  Researchers Wiesenfield, Schatz and Bennett at the Georgia Institute of Technology recently conducted an experiment with pendulum clocks (i.e., “nondigital” clocks) and “laser monitoring that records the pendulum swings for computer analysis[1].”  Based on their results, they concluded that the motion of the pendulum swings caused “imperceptible” motions in the platform to which the clocks were attached, which in turn caused the synchrony (or more properly, “antisynchrony”) of the pendulum swings themselves.  This confirmed Dutch astronomer and physicist Hugyens’ suggestion, way back in 1665, “that the swinging of the pendulums somehow cause the platform to move “imperceptibly.[2]


In short, “this quality of interactive rhythm,” as Grahn puts it, is mechanical after all.  Therefore, to argue from mechanical synchronization (or, to put it another way, coupled oscillation of a mechanical nature) to putatively pheremonal synchronization (that is, coupled oscillation of a pheremonal nature) is not valid.  Pendulum clocks, drums and menstruation cannot all be lumped together in one grand category of synchronous phenomena.


Which is not to say that “one grand category of synchronous phenomena” doesn’t exist:  In her article, “Huygens’s Clocks Revisited,” writer Erica Klarreich tells us:


The Georgia Tech team is now trying to extend its mathematical analysis to formulate a single law that would apply to all coupled oscillators and predict under what conditions they will become synchronized or antisynchronized.  “It looks as if there is a mathematical principle that would be equally valid in all these cases…[3]


But, just as more than 300 years have passed since the synchronization of pendulum clocks had first been observed, it may be another 300 years before any “theory of general synchrony” is formulated, and where menstruation will fit into it, is anybody’s guess.


Now let’s take a look at what Strassmann has to say about the “menstrual/lunar correspondence” suggested by Grahn:


It has been postulated that menstrual synchrony is caused by the lunar cycle, but reports conflict on whether menstrual onsets predominate during the full moon (Cutler et al., 1987), the new moon (Law, 1986), or are random with respect to lunar phase (Gunn et al., 1937; Pochobradsky, 1974).  Dogon villagers did not have electric lighting and spent most nights outdoors, talking and sleeping, so they were an ideal population for detecting a lunar influence.  None, however, was found (Strassmann, 1997).”


It’s interesting to note that Grahn makes frequent references to Dogon beliefs and customs in her book; the same Dogon (a people in Mali, West Africa), in which Strassmann found no lunar influence on menstrual synchrony; nor, in fact any menstrual synchrony at all.  To be fair, “Blood, Bread, and Roses” came out in 1993, and Strassmann’s paper in 1997.  But this highlights the point that menstrual synchrony research, far from being “over and done with,” is an ongoing field of inquiry, requiring a willingness to engage with new information as it emerges.


It’s also worth noting that both females and males produce reproductive fluids – as well as a number of other bodily fluids.   Why not try rewriting the above passage, substituting “seminal” for “menstrual,” or perhaps even using “urinal.”  In Grahn’s book, she delves into the menstrual mythologies of numerous cultures – why not see what kind of seminal mythologies exist, or even “urinal” mythologies.


Both Twilfong and Grahn use menstrual synchrony as a way of interpreting the distant past and understanding the origins of human culture, giving importance, and even centrality, to menstruation.  Click here for an example from this curator of using menstrual synchrony to look back less than half a century.


[1] Out of Time: Researchers Recreate 1665 Clock Experiment to Gain Insights Into Modern Synchronized Oscillators,” John Toon, September 8, 2000


Michael Schatz: E-mail:

Kurt Wiesenfeld: E-mail:


[2] Ibid.


[3]Huygens’s Clocks Revisited,” Erica Klarreich, July-August, 2002, Science Observer


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