It is well known that women feel attracted to certain visual, auditory, and olfactory characteristics of men. This attraction seems to be hormonally regulated, as suggested by psychosexual studies of women at different phases of the menstrual cycle. In general, women are more strongly attracted to male characteristics during the estrogen-dominant phase of their cycle (first two-thirds) than during the progesterone-dominant phase (last third).
This cyclical change has been most recently shown by Rupp et al. (2009). MRI scans were used to measure how female brains process pictures of male faces that morphing software had either masculinized or feminized. The subjects were tested on days 10-12 and days 19-23 of the menstrual cycle. Measurements were taken of their levels of estradiol, progesterone, free testosterone, and total testosterone. The subjects also filled out questionnaires about their psychosexual profile (propensity for short-term sexual encounters, for sexual excitation, for sexual inhibition, etc.).
During the first time window (days 10-12), five brain regions showed a stronger neural response to masculinized faces than to feminized faces. No brain region showed the reverse pattern. During the second time window (days 19-23), only one region responded more to masculinized faces than to feminized faces. For both windows, some regions showed significant correlations between neural activation and hormone level. Estradiol correlated positively with neural activation whereas progesterone correlated negatively. The correlations were negative or positive for free and total testosterone. In some brain regions, neural activation also correlated with psychosexual variables.
What was driving these neural responses? What facial feature was turning these women on? In response to an e-mail, the lead author, Heather Rupp, told me that the morphing software had varied the shape of the male faces and their skin tone. The masculinized faces were darker-skinned and the feminized faces lighter-skinned. Her results may thus dovetail with my own findings on female preferences with regard to male skin tone, i.e., my subjects more strongly preferred darker male faces during the estrogen-dominant phase of their menstrual cycle than during the progesterone-dominant phase (Frost 1994).
Frost P. (1994). Preference for darker faces in photographs at different phases of the menstrual cycle: Preliminary assessment of evidence for a hormonal relationship, Perceptual and Motor Skills, 79, 507-514.
Rupp, H.A., T.W. James, E.D. Ketterson, D.R. Sengelaub, E. Janssen, and J.R. Heiman. (2009). Neural activation in women in response to masculinized male faces: mediation by hormones and psychosexual factors. Evolution and Human Behavior, 30, 1-10.