Preliminary Findings: the Effect of Menstrual Cycle and Birth-Control Upon Women's Evaluations of Men's Bodies

Women’s attraction to men’s secondary sexual characteristics- such as facial structure, voice pitch, and body type- has been shown to vary as a function of the menstrual cycle, becoming positively augmented during the late-folicular phase. Evolutionarily, this effect is hypothesized to occur because it profited a woman to be more proceptive during her most fertile period. The proximate mechanism by which this effect is thought to be mediated is the fluctuation of hormones, which dictate a normal menstrual cycle. Research has shown the introduction of hormonally based birth-control has effects on women’s behavior, most saliently, libido. And as birth-control greatly alters the production and regulation of certain hormones during the menstrual cycle, it follows that women taking birth-control should no longer express differential attraction to secondary traits. With the exception of the authors’ past work, research has omitted birth-control as a factor. This experiment was designed to detect differential evaluation of men’s bodies as a function of the menstrual cycle; also, the effect of birth-control was investigated. 37 women participated in a repeated-measures experiment (On birth-control group: n= 15, average age= 21.76±2.14; Off birth-control group: n= 22, average age = 21.14±1.7). Sexual orientation was controlled for, as only heterosexual women’s data were used. Interval between the first and second iteration of the experiment was on average 17 days. Subjects rated the attractiveness of two sets of images of men’s bodies. Each set contained nine drawings of men that systematically differed in fat and muscle proportion, which created a spectrum.  The stimuli were got from past studies and had shown to be statistically reliable. Rating was done on a one hundred point, sliding scale. Results indicate that both cycle and birth-control did affect evaluations of men’s bodies. Repeated- measures ANOVA revealed women’s evaluations differed from the first to the second time the experiment was taken, consistently. Women taking birth-control, however, did not display this effect. In some cases, the cycle day significantly correlated with attractiveness scores produced. Results, though varied, indicate that both birth-control and cycle affect women’s evaluation of men’s bodies. These results are interpreted through evolutionary theory.