Women using the birth control pill prefer men with less masculine faces compared to nonusers, new research suggests.
Millions of women use hormonal forms of contraception, and some studies indicate the pill could affect partner preferences. A new study shows women were attracted to less masculine male faces after going on the pill, while their ratings of the attractiveness of female faces were unaffected. And in couples who first met when the woman was on the pill, the men were less likely to have manly faces than those who met when the woman was off the pill. If supported, the findings could have important implications for how relationships are formed.
Many factors can influence human attractiveness. Some research suggests that a preference for masculine or feminine traits may be linked to genetic benefits for a couple's offspring, such as strong immune systems. And a few studies have found that women prefer more masculine traits during the fertile phase of their menstrual cycle. The new study investigated how the pill affects these preferences.
Facial attraction
The study, detailed online March 23 in the journal Psychoneuroendocrinology, compared the romantic preferences of straight women ages 18 to 24 who were taking oral contraception against those who were not. Researchers showed the women composite images of young male and female faces, which could be manipulated to appear more or less masculine (based on features like cheekbone prominence, jaw height and face width). Scientists then told the participants to alter the male faces so they were most attractive for either a short- or long-term relationship, and to alter the female faces simply to be the most attractive.
The women were tested twice — once when none of them were taking the pill and again three months after some began using the pill. The women themselves decided whether to join the pill-taking group or not. [7 Surprising Facts About The Pill]
When women were taking the pill, they preferred less masculine male faces (those with more narrow jawbones and more rounded faces, for instance) than before they started taking birth control, the results showed. Being on the pill had no effect on preference for masculinity in female faces.
Choosing a partner
Next, the researchers looked at whether taking the pill influenced women's choices of partners. The scientists compared 85 couples who reported using the pill when they met to 85 couples who reported not using it. Researchers took photos of the faces of the men in each couple and had volunteers judge the manliness of each. The volunteers also rated computer-tweaked versions of the images that accentuated differences in masculinity, for instance making a wide lower jawline (a manly trait) even wider .
Researchers found that the volunteers rated the partners of women who weren't on the pill at the start of their relationships as more masculine than those of women who were on the pill. They rated the computer-manipulated images along the same lines. The link between the pill and facial traits was also confirmed with a mathematical formula.
Even so, the study is correlational and therefore cannot say that the pill, rather than some other variable, causes these mate preferences, said ecologist and evolutionary biologist Claus Wedekind of the University of Lausanne, Switzerland.
Even though the study is interesting and well done, Wedekend said, it faces limitations because it's not a double-blind experiment, a rigorous condition under which neither participants nor researchers know who's in the experimental group. For example, women who choose to take the pill may be biased toward men who are more "stable" and less masculine-looking, Wedekind said, or "may have an idea already what the pill does to them, and that influences the experiment."
Yet given how widely the pill is used, its potential role in how women choose their partners could have far-reaching effects.
Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on LiveScience.com.
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