Scientists have long known that women's preferences for masculine men change throughout their menstrual cycles. A new study from Indiana University's Kinsey Institute is the first to demonstrate differences in brain activity as women considered masculinized and feminized male faces and whether the person was a potential sexual partner.
The researchers identified regions of the brain that responded more strongly to masculine faces and demonstrated that differences between masculinized and feminized faces appeared strongest when the women were closer to ovulating.
Previous studies have shown that women's sexual preference for facial characteristics vary depending on their menstrual phase. These fluctuating preferences are thought to reflect evolutionarily founded changes in women's reproductive priorities. Around the time of ovulation women prefer more masculinized faces -- faces with features that indicate high levels of testosterone. These facial cues predict high genetic quality in the male because only such males can afford the immune-compromising effects of testosterone. Testosterone may be costly for the males' mates as well because high testosterone levels also are associated with high rates of offspring abandonment.
Around the time of ovulation, a female's preference apparently shifts from avoiding negligent parenting to acquiring the best genes for her offspring. At other points during the cycle, women will prefer more feminized male faces, as they might signal a higher willingness of the males to invest in offspring.
Researchers found differences in brain regions related to face perception, decision making and reward processing that responded more strongly to masculinized than feminized faces, suggesting that "neural activation in response to face stimuli is sensitive to facial masculinization, even in the absence of differences in subjective ratings." Differences between masculinized and feminized faces appeared strongest during the follicular phase, closer to ovulation.
