The story begins when Martha McClintock published a rather sensational article for Nature in 1971 where she claimed that women who live together tend, for example, in college dorms, tend to synchronize their menstrual cycles. Her research was based on another article that showed that female rats do the same (though their cycle is only few days long), and further work showed that this phenomena exists in other mammals (notably, in chimps).
However, McClintock failed to explain the mechanism behind such synchronism or give any evolutionary explanation for the its existence. Naturally, it faces a lot of criticism, culminating in the 90's (but the debate between pro synchronists and those against it linger on). The critics point to the fact that since different women don't have the same cycle length, synchronism, if any, is just temporary. Moreover, they show errors in the statistical analysis carried by McClintock and others, and even claim there's no evidence for synchronism in rats. See this column on Straight Dope for a short review of McClintock's and her critics' claims.
But I don't care about it. I believe that unless we will lock up female couples in tight cells with no interaction with other females (and probably no interaction with other males), even if there is a mechanism that provides cycle synchronism, we won't notice it working. The signal to noise ratio is too high to see any evidence for such synchronism.
To show my point, I coded a quick simulation of female students. The simulation consisted of
100 students, each having a roommate, a best friend, and a casual friend. If student A is a roommate or best friend of student B, student B is a roommate or best fried of student A. However student A can be a casual friend of B without B being the casual friend A.
Every hour, each student is meeting one other student in random. There's 48% chance she would meet with her roommate, 24% chance she would meet with her best friend, 12% chance she would meet with her casual friend, and 16% she would meet with a random student in the dorm. In real life that would mean, about 12 hours are spent daily with your roommate, 6 with your best friend.
When two students meet up, they compare their cycle. If A is after her menstrual phase in her cycle, while B is before it in her cycle, A prolongs her next cycles by an hour, while B shortens her by an hour. This would ideally make their next cycle more synchronized.
Each student enrolls to the dorms with a cycle of between 27 and 33 days, and a random offset within it (that is, random number of days until her next menstrual phase).
What happens after 365 days? Does a student cycle become more similar to the cycles of her friends (that is, the difference between her offset and the weighted average of her roommate and friends offset)? If not, does her menstrual phase align just with her roommate?
The answer to all those questions (according to my simulation) is a resounding NO. There is no evidence that the students and her friends have more aligned cycle after a year. Here's a representative output of my simulation, displaying the offset in hours between a student's cycle and the weighted average of her friends' cycle, and between her cycle and her roommate's.
Before enrolling to dorms
distance from roommate= 232 distance from friends+roommate= 230
After a year
distance from roommate= 255 distance from friends+roommate= 254
If anything, enrolling to the dorms only makes the student less alike her friends when it comes to her menstrual cycle. I acknowledge I may have some bugs with my simulation and some false assumptions (I have to leave in a couple of hours to take a flight), but I have a feeling the bugs eliminate each other.
Therefore, I think that this simulation shows that even if there is a mechanism that synchronizes females' cycles, we won't notice it. What do you think?
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1 comments:
I don't understand where you've taken the probabilities from?
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