Women Who Stay Together, Bleed Together

It has been discovered that when female mice are housed together and isolated from males their oestrous cycles seem to synchronize. This doesn't happen when female mice are housed alone. Synchrony has also been found in female mice isolated with bedding from a cage full of female mice. The phenomenon has been named the Lee-Boot effect and is caused by a specific pheromone found in mouse urine.

More than three decades ago, Martha McClintock - Harvard University - observed that the menstrual cycles of women who lived together in dormitories tended to synchronize and lengthen. Her findings have been some of the strongest indicators for the existence of pheromones in humans. Since then, she has started a wave of studies on menstrual synchrony.

Michael Russell exposed female subjects to a mixture of alcohol and a female colleague's underarm scent. The result was that half of the women were in exact menstrual synchrony with Russell's colleague.

So why does this happen? Menstrual synchrony makes sense in pack animals like chimps because typically, if the females become pregnant together they will most likely give birth at around the same time, allowing for the "village to raise the children". But in humans this hardly seems practical. Another interpretation could be that there are dominant women with regards to menstrual synchrony, again something found in the animal kingdom but doesn't seem to make much sense in humans today.

This has been by far one of the strangest things I have ever encountered and being a guy I have even less knowledge of individual menstruation let alone group synchrony.

The world is your oyster.

PS: I hope no one takes the title of this entry out of context and becomes offended...