The study exposed a group of women to a whiff of perspiration from other women. It was found that it caused their menstrual cycles to speed up or slow down depending on the time in the month the sweat was collected; before, during, or after ovulation. Therefore, this study proposed that there are two types of pheromone involved: "One, produced prior to ovulation, shortens the ovarian cycle; and the second, produced just at ovulation, lengthens the cycle".How does pheromones effect menst. Cycle and why?

No one has a definitive reason why this happens. No one is really sure of the cause, many believe it doesn't happen but if you ask any woman who has lived with other women, it is apparent this exists.

Some say it has to do with male hormones, but I am inclined to reject that. While growing up I was in several group homes that were male free zones and within 3 months every new resident was synchronized to the rest of us, including staff.

Some think it was a survival mechanism to limit the number of births. I think this may be possible. If an entire tribe is fertile only one week out of the month, it is a lot easier to control population growth. But I am not sure there is any concrete proof of this, just another theory.