infradian and ultradian rhythms

• evolutionary basis of menstrual cycle - may have been advantageous for females to menstruate together and fall pregnant at same time so that new born could be cared for collectively within the social group to increase chances of offsprings survival. some argue this would produce competition so avoidance of synchrony may be most adaptive evolutionary strategy and therefore naturally selected
• evidence for REM sleep - dement and kleitman studied 9 participants sleep patterns in a sleep lab. Brainwave activity was recorded on EEG and researchers controlled for effects of caffeine and alcohol. REM activity during sleep was highly correlated with experience of dreaming, brain wave activity varied according to how vivid dreams were. participants woken during this time reported having a very accurate recall of their dreams. sample size was criticised