Liz, I don't think it has to be that large a group - we've had it at school, too. Primary school, so only the staff involved. Useful, if taken by surprise - someone else would have supplies. And someone going through a bad menopause could wreak havoc on those not on the pill. This is anecdotal, not reviewed research. There was research done with a convent in the States (I think), which had the entrained cycles - the researcher then introduced testosterone to the air conditioning (that's why I think it was the States), and found that the cycles became shorter. Then the Reverend Mother found out, and stopped the experiment. We do have men around at school. I expect you would need a certain proportion, or that they have to arouse interest in the women to have an effect. One aspect of human cycles which would not apply in chimps is that our minds (emotions in this case) can drive our bodies, even such apparently involuntary matters.

Incidentally, I have read that the Ayatolla Khomeini interpreted the teachings of Islam as that if a woman was praying, and her period began during the prayer, the prayer was void. What sort of God is that?

Penny