Facial appearance is a cue to oestrogen levels in women.

Although many accounts of facial attractiveness propose that femininity in women's faces indicates high levels of oestrogen, there is little empirical evidence in support of this assumption. Here, we used assays for urinary metabolites of oestrogen (oestrone-3-glucuronide, E1G) and progesterone (pregnanediol-3-glucuronide, P3G) to investigate the relationship between circulating gonadal hormones and ratings of the femininity, attractiveness and apparent health of women's faces. Positive correlations were observed between late follicular oestrogen and ratings of femininity, attractiveness and health. Positive correlations of luteal progesterone and health and attractiveness ratings were marginally significant. Ratings of facial attributions did not relate to hormone levels for women wearing make-up when photographed. There was no effect of sex of rater on the relationships between oestrogen and ratings of facial appearance. These findings demonstrate that female facial appearance holds detectable cues to reproductive health that are considered attractive by other people.

Menstrual cycle, pregnancy and oral contraceptive use alter attraction to apparent health in faces.

Previous studies demonstrating changes in women's face preferences have emphasized increased attraction to cues to possible indirect benefits (e.g. heritable immunity to infection) that coincides with periods of high fertility (e.g. the late follicular phase of the menstrual cycle). By contrast, here we show that when choosing between composite faces with raised or lowered apparent health, women's preferences for faces that are perceived as healthy are (i) stronger during the luteal phase of the menstrual cycle than during the late follicular, fertile phase, (ii) stronger in pregnant women than in non-pregnant women and (iii) stronger in women using oral contraceptives than in women with natural menstrual cycles. Change in preference for male faces was greater for short- than long-term relationships. These findings indicate raised progesterone level is associated with increased attraction to facial cues associated with possible direct benefits (e.g. low risk of infection) and suggest that women's face preferences are influenced by adaptations that compensate for weakened immune system responses during pregnancy and reduce the risk of infection disrupting foetal development.

Voice pitch predicts reproductive success in male hunter-gatherers.

The validity of evolutionary explanations of vocal sexual dimorphism hinges upon whether or not individuals with more sexually dimorphic voices have higher reproductive success than individuals with less dimorphic voices. However, due to modern birth control methods, these data are rarely described, and mating success is often used as a second-rate proxy. Here, we test whether voice pitch predicts reproductive success, number of children born and child mortality in an evolutionarily relevant population of hunter-gatherers. While we find that voice pitch is not related to reproductive outcomes in women, we find that men with low voice pitch have higher reproductive success and more children born to them. However, voice pitch in men does not predict child mortality. These findings suggest that the association between voice pitch and reproductive success in men is mediated by differential access to fecund women. Furthermore, they show that there is currently selection pressure for low-pitch voices in men.

Raised salivary testosterone in women is associated with increased attraction to masculine faces.

Women's preferences for masculinity in men's faces, voices and behavioral displays change during the menstrual cycle and are strongest around ovulation. While previous findings suggest that change in progesterone level is an important hormonal mechanism for such variation, it is likely that changes in the levels of other hormones will also contribute to cyclic variation in masculinity preferences. Here we compared women's preferences for masculine faces at two points in the menstrual cycle where women differed in salivary testosterone, but not in salivary progesterone or estrogen. Preferences for masculinity were strongest when women's testosterone levels were relatively high. Our findings complement those from previous studies that show systematic variation in masculinity preferences during the menstrual cycle and suggest that change in testosterone level may play an important role in cyclic shifts in women's preferences for masculine traits.

Menstrual cycle, trait estrogen level, and masculinity preferences in the human voice.

Men with low testosterone (feminine men) invest in relationships and offspring more than men with high testosterone (masculine men). Women's attraction to testosterone dependent traits (e.g. masculine face shape) is enhanced during the late-follicular, fertile phase of the menstrual cycle. Attractive, feminine women have stronger preferences for masculine men as possible long-term partners than less attractive, masculine women. We manipulated 2 testosterone related vocal traits (voice pitch and apparent vocal-tract length) in voices to test if women prefer masculinized men's voices to feminized men's voices; masculinity preferences are enhanced at the fertile (late-follicular) menstrual cycle phase; the amount that masculinity preferences shift cyclically relates to average estrone-3-glucuronide concentration (the primary urinary metabolite of estrone, E3G). We found women displayed general masculinity preferences for men's voices; masculinity preferences were greater in the fertile (late-follicular) phase of the cycle than the non-fertile (early-follicular and luteal) phase; and this effect was most pronounced for women with low average E3G concentration. As feminine women (i.e. those with high average E3G levels) are most able to obtain investment even from masculine men, these women may not need to change their mating preference or strategy during the menstrual cycle as much as masculine women.

Commitment to relationships and preferences for femininity and apparent health in faces are strongest on days of the menstrual cycle when progesterone level is high.

Previous studies of changes in women's behavior during the menstrual cycle have offered insight into the motivations underpinning women's preferences for social cues associated with possible direct benefits (e.g., investment, low risk of infection) and indirect benefits (e.g., offspring viability). Here we sought to extend this work by testing for systematic variation in women's preferences for male and female faces and in their attitudes to their romantic relationship during the menstrual cycle. In Study 1, we found partnered women's reported commitment to their romantic relationship and preferences for femininity in male and female faces were strongest on days of the menstrual cycle when progesterone levels are increased (and fertility is low). Happiness in relationships did not change across the cycle. In Study 2, we found that the effect of cycle phase on women's preference for feminine faces was independent of increased attraction to apparent health in faces during the luteal phase. Collectively, these findings are further evidence that women's preferences for social cues associated with possible direct benefits and commitment to relationships are strongest during conditions characterized by raised progesterone level, while attraction to men displaying cues associated with possible indirect benefits is strongest when women are most fertile.