Anthony C. Little

Facial attractiveness: evolutionary based research

Face preferences affect a diverse range of critical social outcomes, from mate choices and decisions about platonic relationships to hiring decisions and decisions about social exchange. Firstly, we review the facial characteristics that influence attractiveness judgements of faces (e.g. symmetry, sexually dimorphic shape cues, averageness, skin colour/texture and cues to personality) and then review several important sources of individual differences in face preferences (e.g. hormone levels and fertility, own attractiveness and personality, visual experience, familiarity and imprinting, social learning). The research relating to these issues highlights flexible, sophisticated systems that support and promote adaptive responses to faces that appear to function to maximize the benefits of both our mate choices and more general decisions about other types of social partners.

Symmetry, sexual dimorphism in facial proportions and male facial attractiveness

Facial symmetry has been proposed as a marker of developmental stability that may be important in human mate choice. Several studies have demonstrated positive relationships between facial symmetry and attractiveness. It was recently proposed that symmetry is not a primary cue to facial attractiveness, as symmetrical faces remain attractive even when presented as half faces (with no cues to symmetry). Facial sexual dimorphisms (‘masculinity’) have been suggested as a possible cue that may covary with symmetry in men following data on trait size/symmetry relationships in other species. Here, we use real and computer graphic male faces in order to demonstrate that (i) symmetric faces are more attractive, but not reliably more masculine than less symmetric faces and (ii) that symmetric faces possess characteristics that are attractive independent of symmetry, but that these characteristics remain at present undefined.

Female facial attractiveness increases during the fertile phase of the menstrual cycle

The lack of obvious visible manifestations of ovulation in human females, compared with the prominent sexual swellings of many primates, has led to the idea that human ovulation is concealed. While human ovulation is clearly not advertised to the same extent as in some other species, we show here that both men and women judge photographs of womens faces that were taken in the fertile window of the menstrual cycle as more attractive than photographs taken during the luteal phase. This indicates the existence of visible cues to ovulation in the human face, and is consistent with similar cyclical changes observed for preferences of female body odour. This heightened allure could be an adaptive mechanism for raising a females relative value in the mating market at the time in the cycle when the probability of conception is at its highest.

Correlated preferences for facial masculinity and ideal or actual partner's masculinity

Studies of womens preferences for male faces have variously reported preferences for masculine faces, preferences for feminine faces and no effect of masculinity–femininity on male facial attractiveness. It has been suggested that these apparently inconsistent findings are, at least partly, due to differences in the methods used to manipulate the masculinity of face images or individual differences in attraction to facial cues associated with youth. Here, however, we show that womens preferences for masculinity manipulated in male faces using techniques similar to the three most widely used methods are positively inter-related. We also show that womens preferences for masculine male faces are positively related to ratings of the masculinity of their actual partner and their ideal partner. Correlations with partner masculinity were independent of real and ideal partner age, which were not associated with facial masculinity preference. Collectively, these findings suggest that variability among studies in their findings for womens masculinity preferences reflects individual differences in attraction to masculinity rather than differences in the methods used to manufacture stimuli, and are important for the interpretation of previous and future studies of facial masculinity.

Commitment to relationships and preferences for femininity and apparent health in faces are strongest on days of the menstrual cycle when progesterone level is high.

Previous studies of changes in womens behavior during the menstrual cycle have offered insight into the motivations underpinning womens preferences for social cues associated with possible direct benefits (e.g., investment, low risk of infection) and indirect benefits (e.g., offspring viability). Here we sought to extend this work by testing for systematic variation in womens preferences for male and female faces and in their attitudes to their romantic relationship during the menstrual cycle. In Study 1, we found partnered womens reported commitment to their romantic relationship and preferences for femininity in male and female faces were strongest on days of the menstrual cycle when progesterone levels are increased (and fertility is low). Happiness in relationships did not change across the cycle. In Study 2, we found that the effect of cycle phase on womens preference for feminine faces was independent of increased attraction to apparent health in faces during the luteal phase. Collectively, these findings are further evidence that womens preferences for social cues associated with possible direct benefits and commitment to relationships are strongest during conditions characterized by raised progesterone level, while attraction to men displaying cues associated with possible indirect benefits is strongest when women are most fertile.

Raised salivary testosterone in women is associated with increased attraction to masculine faces.

Womens preferences for masculinity in mens faces, voices and behavioral displays change during the menstrual cycle and are strongest around ovulation. While previous findings suggest that change in progesterone level is an important hormonal mechanism for such variation, it is likely that changes in the levels of other hormones will also contribute to cyclic variation in masculinity preferences. Here we compared womens preferences for masculine faces at two points in the menstrual cycle where women differed in salivary testosterone, but not in salivary progesterone or estrogen. Preferences for masculinity were strongest when womens testosterone levels were relatively high. Our findings complement those from previous studies that show systematic variation in masculinity preferences during the menstrual cycle and suggest that change in testosterone level may play an important role in cyclic shifts in womens preferences for masculine traits.

The health of a nation predicts their mate preferences: cross-cultural variation in women's preferences for masculinized male faces

Recent formulations of sexual selection theory emphasize how mate choice can be affected by environmental factors, such as predation risk and resource quality. Women vary greatly in the extent to which they prefer male masculinity and this variation is hypothesized to reflect differences in how women resolve the trade-off between the costs (e.g. low investment) and benefits (e.g. healthy offspring) associated with choosing a masculine partner. A strong prediction of this trade-off theory is that womens masculinity preferences will be stronger in cultures where poor health is particularly harmful to survival. We investigated the relationship between womens preferences for male facial masculinity and a health index derived from World Health Organization statistics for mortality rates, life expectancies and the impact of communicable disease. Across 30 countries, masculinity preference increased as health decreased. This relationship was independent of cross-cultural differences in wealth or womens mating strategies. These findings show non-arbitrary cross-cultural differences in facial attractiveness judgements and demonstrate the use of trade-off theory for investigating cross-cultural variation in womens mate preferences.

Sex-contingent face after-effects suggest distinct neural populations code male and female faces

Exposure to faces biases perceptions of subsequently viewed faces. Faces similar to those seen previously are judged more normal and attractive than they were prior to exposure. Here we show sex-contingent after-effects following adaptation to eye-spacing (experiment 1), facial identity (experiment 2) and masculinity (experiment 3). Viewing faces of one sex with increased eye-spacing and faces of the other sex with decreased eye-spacing simultaneously induced opposite after-effects for male and female faces (assessed by normality judgments). Viewing faces transformed in identity or masculinity increased preferences for novel faces with characteristics similar to those viewed only when the sex of the faces presented in the adaptation phase and in post-adaptation preference tests were congruent. Because after-effects reflect changes in responses of neural populations that code faces, our findings indicate that distinct neural populations code male and female faces.

Effects of Menstrual Cycle Phase on Face Preferences

While many studies of face preferences have emphasized high agreement among individuals about the types of faces they consider attractive and unattractive, other studies have demonstrated systematic variation in face preferences. Here, we review the evidence that women’s preferences for masculinity, apparent health, and self-resemblance in faces change systematically during the menstrual cycle. Our review focuses on the proximate mechanisms that might underpin these changes (i.e., what changes in hormone levels are important for effects of menstrual cycle phase) and the possible functions of these changes (i.e., to maximize the likelihood that offspring inherit strong immune systems or to increase the likelihood of successful pregnancy by either promoting affiliation with individuals who will provide support and care during pregnancy or by promoting strategies to avoid contagion during social interactions). While evidence that differentiates between these two accounts of the function of cyclic shifts in face preferences is currently equivocal for masculinity preferences, there is compelling evidence that the function of the effects of menstrual cycle phase on preferences for apparent health and self-resemblance in faces is to increase the likelihood of successful pregnancy.

Preferences for masculinity in male bodies change across the menstrual cycle.

In human females cyclic shifts in preference have been documented for odour and physical and behavioral male traits. Women prefer the smell of dominant males, more masculine male faces and men behaving more dominantly when at peak fertility than at other times in their menstrual cycle. Here we examine variation in preferences for body sexual dimorphism. Across two studies, both between- and within-participant, we show that women prefer greater masculinity in male bodies at times when their fertility is likely highest, in the follicular phase of their cycle. Shifts were seen when rating for a short-term but not when rating for a long-term relationship. In line with studies showing similar effects for facial sexual dimorphism, we also show that women prefer greater masculinity when they think themselves attractive than when they think themselves less attractive. These results indicate that womens preferences for sexual dimorphism in male bodies follow a similar pattern as found for sexual dimorphism and dominance in other domains and such differences in preference may serve a similar function. Cyclic preferences could influence women to select partners when most likely to become pregnant that possess traits that may be most likely to maximize their offsprings quality via attraction to masculinity or serve to help acquire investment via attraction to femininity.