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What makes some faces particularly beautiful? One of the more influential hypotheses about women’s facial beauty is that attractive facial characteristics signal that a woman is not susceptible to infectious illnesses and that she has healthy levels of the estradiol and progesterone. Such women are thought to be attractive, because they will be good mates and produce healthy kids. Exaggerated feminine facial characteristics, such as large eyes and a refined, small jaw, are thought to play a critical role in both beauty and health signaling. These types of arguments might explain why people from different cultures and people of different ages generally agree about what faces are beautiful.

Recent work has challenged this influential hypothesis, however. For example, two recent studies, each of around 250 women, found no evidence that more attractive women had higher levels of estradiol or progesterone. Two other recent studies, one that my colleagues and I conducted with nearly 600 women and another that involved 80 women, found no evidence that women with more attractive faces were less susceptible to infectious illness. Together, these findings suggest that women with more attractive faces are not necessarily healthier.

What about the claim that femininity plays a critical role in women’s facial ? It’s true that when feminine facial characteristics are increased in images of women’s faces (and no other characteristics are affected), these image manipulations have a strong positive effect on attractiveness. However, studies that measured the femininity of women’s faces have consistently found that femininity is actually a relatively poor predictor of women’s facial attractiveness. Other candidate cues for attractiveness, such as averageness, also fared poorly in these studies. Instead, this work suggests that measures of coding efficiency are a particularly good predictor of women’s facial attractiveness.

Evolutionary psychologists have long thought that facial attractiveness was a health cue. However, recent work suggests that it might simply be a byproduct of how easy some faces are for the brain to encode.