have we too much blood up in us or what O patience above its pouring out of me like the sea


Menstrual synchrony was first demonstrated in a 1971 paper published in Nature by Martha McClintock. […]

she asked 135 college girls living in dorms to recall their period start dates at three times throughout the academic year. She found that close-friend groups had periods significantly closer together in April (later in the year) compared with October: lessening from an average of 6.4 to 4.6 days apart.

The phenomenon was dubbed “the McClintock effect” and is widely held as the first example of pheromones — unconscious chemical signals that influence behavior and physiology — among humans. […] Many subsequent researchers went on to reproduce the results from McClintock’s original experiment in people, rats, hamsters and chimpanzees.

But a cohort of studies that found no evidence for menstrual synchrony began to grow, too. […]

In 1992 H. Clyde Wilson […] re-analyzed McClintock’s first experiment, along with a few others that used a similar design. He found that all had inflated the difference between period start dates at the beginning of their studies […] their model of two pheromones — one that pulls ovulation forward and one that delays it — driving synchrony didn’t work […]

The insurmountable hurdle in all the studies is that women often have persistent cycles of different lengths. As such, they can never truly synchronize, just randomly phase in and out of synchrony over the months as their cycles diverge and converge. […]

But a team of Japanese researchers at Yokohama City University, led by Kazuyuki Shinohara, also found in a series of papers that donor women undergoing these two phases of the menstrual cycle release compounds that when inhaled by other women can significantly impact the frequency in the latter of pulses of luteinizing hormone (LH), which helps control the timing of ovulation and cycle length.

{ Scientific American | Continue reading }