About face. Fertile women preferred computer-generated faces that were more masculine (right) than feminine (left).

Beauty in the Hormones of the Beholder

What makes a guy handsome? That depends on a woman's period, researchers report in tomorrow's issue of Nature. During days of the month when they are likely to conceive, women are more attracted to relatively more masculine mug shots. When less likely to conceive, women prefer more feminine features. The researchers speculate that evolution may have favored women who settled down with more feminine guys but had occasional flings with testosterone-loaded studs In a previous study, psychologist Ian Penton-Voak of the University of St. Andrews in Fife, Scotland, and his colleagues in the United Kingdom and Japan found that women generally prefer male faces with a slightly more feminine look--with smaller jaws and cheekbones, for example. The women associated such faces with honesty, warmth, and better parenting skills.

To see if this preference is swayed by hormonal changes, team members in Japan showed women computer-generated faces made by digitally blending photographs of several dozen men and women. They asked women to choose the most "physically attractive" face, making note of where a woman was in her monthly cycle. During the time they were most likely to conceive, women preferred faces that were 10% more feminine than the average male. But when they were unlikely to conceive, the average preference was for faces that were 20% more feminine.

In the United Kingdom, the researchers changed the question slightly, asking women to choose the most attractive partner for a "short-term sexual relationship" or a "long-term relationship." Choices for long-term relationships did not vary, but when asked to chose a partner for a fling, women in a fertile phase of their cycle chose relatively less feminine faces. The researchers speculate that evolution may have favored women who had long-term relationships with more feminine, nurturing partners, but occasional liaisons with more masculine-appearing men when conception was most likely. Some studies have suggested that higher testosterone levels--signaled by more masculine features--might correlate with a more robust immune system.

Such links are far from clear, cautions ethologist Stefano Ghirlanda of Stockholm University, who notes that other studies have found no connection between physical beauty and actual health. But psychologist Michael Cunningham of the University of Louisville in Kentucky says the results are plausible. "I find it entirely credible that hormones would influence selection" of face shapes, he says.