Plasma gonadotropin levels throughout the regular menstrual cycle in 10 Japanese women were measured daily using radioimmunoassay. It is, therefore, suggested that the low frequency of dizygotic twinning in Japanese women might be related to their low output of gonadotropin. Serum gonadotropin levels in Japanese women. Salivary testosterone and creative musical behavior in adolescent males and females. Women were proportionate to men, with Orientals having smaller vaginas and blacks larger ones, relative to Caucasians.
Recent data show similar patterns.
Several subsequent studies are confirmatory. Testing an evolutionary hypothesis. Although this is a preliminary study, the evidence for synchrony and suppression of the menstrual cycle is quite strong, indicating that in humans there is some interpersonal physiological process which affects the menstrual cycle. However, while the right field advantage for lexical decisions did not change throughout the menstrual cycle, the significant left field advantage for face perception in the menstrual phase disappeared during the mentrual cycle and even shifted in the prementrual phase, suggesting that hormones may influence the balance of hemispheric activation. Such influences might at least in part be responsible for more variable results with female than with male subject groups and for contradictions between different experiment studies.