Can you trust this man? What sounds like an everyday question, is indeed a classic problem of human evolution, especially as seen from a female perspective. According to evolutionary theories, women should have different levels of trust dependent on their actual menstrual cycle. This prediction was tested by Biological Psychologists and Psychiatrists from Bochum University. They tested how trusting behavior varies in naturally cycling women, as a function of sex and attractiveness of players in a trust game, at three distinct phases of the menstrual cycle. Women acted more cautiously in an investment game at the preovulatory phase, compared to the menstrual and the mid-luteal phase. Reduced willingness to trust in strangers was particularly expressed toward male players at this time. The increase of estradiol levels from menses to the preovulatory phase was negatively correlated with trust in attractive male other players, whereas the increase of progesterone levels from menses to the mid-luteal phase was positively associated with trust in unattractive female other players. Thus, the results emphasize the impact of the menstrual cycle on interpersonal trust, although the exact mode of hormonal action needs to be further investigated.

Ball, A., Wolf, C.S., Ocklenburg, S., Herrmann, B.L., Pinnow, M., Brüne, M., Wolf, O.T., Güntürkün, O. (2013). Variability in ratings of trustworthiness across the menstrual cycle. Biol. Psychol., 93, 52-57.