menstrual cycle

• 28 day cycle with 6 day period of fertility
• can range between 24 and 35 days
• biological aspects - releasing of the egg (ovulation) thickening of the womb - loss of womb lining (menstration)
• oestrogen preovulation - high oestrogen leads to ovulation
• progesterone post ovulation - helps rebuild the wombs lining
• infradium rhythm - longer than 24 hours
• endogenous cycle but can be influenced by exogenous factors
• mcclintok - 135 women synchronised their cycles with friendship groups
• mcclinktok and stern - investigated cycle synching and pheremones - 20 women given pads to wipe on top lip - contained pheremones from women at different stages of cycle
• mcclinktok and stern findings - 68% of women experienced changes to cycle - brought closer to donors cycle
• pros of mcclinktok and stern - some replications with similar results - evolutionary explan women can all be impregnated with the best genes if synched
• cons - pheremones not widely accepted - evolutionary prevents all women being impregnated by one man
• Trevathan - lesbian couples didn't synch - conflicting evidence