Gili Bar-Hillel abhillel at
Mon Feb 10 08:01:46 EST 2003

Jon wrote:
>I'm well aware of the iregular nature of cycles
>(although all three women here are very regular), and
>you are right, I quite explicitly assumed 28 days, but
>on the other hand this is the oft quoted figure, not
>29 days. Indeed i suspect that the iregular nature of
>these things is an evolutionary mechanism to ensure
>that women who can count still pass on their genes.
>I'd be interested to learn if there is any research to
>suggest that a different figure has ever been accepted
>historically or by other cultures.

29 is prime, making it an unwieldy number for many purposes. 28 is much more 
convenient, because it can be broken into smaller units - that is, weeks. 
This alone is enough to create a bias in favor of 28 over 29. I have no idea 
what the exact median cycle length is for women, but I would be very 
surprised if it does not vary with diet, age and culture, and I would be 
even more surprised if primitive cultures knew the exact statistical mean. I 
still think the cycle is *roughly* 28 days, which is *roughly* the length of 
the cycle of the moon - close enough for women to perceive a connection.

I ran a search on the web looking for some more information on this, and 
found the following site:

>From which, the following quotes:

"Have you ever wondered about the connection between your body's 28 day 
cycle and the cycle of the moon? Here's the theory. In the days before 
electricity, women's bodies were influenced by the amount of moonlight we 
saw. Just as sunlight and moonlight affect plants and animals, our hormones 
were triggered by levels of moonlight. And, all women cycled together. 
Today, with artificial light everywhere, day and night, our cycles no longer 
correspond to the moon. "

and also

"It has been shown that calendar consciousness developed first in women 
because their natural body rhythms corresponded to observations of the moon. 
Chinese women established a lunar calendar 3000 years ago. Mayan women 
understood the great Maya calendar was based on menstrual cycles. Romans 
called the calculation of time menstruation, meaning knowledge of the 
menses. In Gaelic, menstruation and calendar are the same word."

Gili Bar-Hillel
Tel-Aviv, tel.(03)5250014

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