Have you ever noticed your menstrual cycle syncing with the other women in your life?It turns out that this occurrence has gained a lot of interest since the 70’s and recently, researchers have found evidence suggesting that the syncing occurs by chance.
In 1971, Dr Martha McClintock studied the menstrual cycles of 135 women and found the date of menstrual onset was more similar among friends/room-mates compared to random pairing of women.
The explanation at the time, popular with the feminist movement, was that it is evolutionary beneficial to fertile with a group of women at the same time to prevent one male reproducing with them all. Living and spending time with other females meant our pheromones could interact and co-operate. So, females unite to prevent becoming a harem!
However, a recent study by Clarke, Henzi and Barrett (2012) contradicts this popular belief. They studied the cycles of female chacma baboons over six years and found that the overlapping does not associate with the risk of becoming a harem. Rather the cycles of the females were nothing more than a chance occurrence; admittedly they sync over time, however they will also un-sync.
Clarke, P. M. R., Henzi, S. P., & Barrett, L. (2012). Estrous synchrony in a nonseasonal breeder: adaptive strategy or population process?. Behavioral Ecology, 23(3), 573-581.
McClintock, M. K. (1971). Menstrual synchrony and suppression. Nature.