Ian S. Penton-Voak

Effects of sexual dimorphism on facial attractiveness

Testosterone-dependent secondary sexual characteristics in males may signal immunological competence and are sexually selected for in several species,. In humans, oestrogen-dependent characteristics of the female body correlate with health and reproductive fitness and are found attractive. Enhancing the sexual dimorphism of human faces should raise attractiveness by enhancing sex-hormone-related cues to youth and fertility in females,, and to dominance and immunocompetence in males,,. Here we report the results of asking subjects to choose the most attractive faces from continua that enhanced or diminished differences between the average shape of female and male faces. As predicted, subjects preferred feminized to average shapes of a female face. This preference applied across UK and Japanese populations but was stronger for within-population judgements, which indicates that attractiveness cues are learned. Subjects preferred feminized to average or masculinized shapes of a male face. Enhancing masculine facial characteristics increased both perceived dominance and negative attributions (for example, coldness or dishonesty) relevant to relationships and paternal investment. These results indicate a selection pressure that limits sexual dimorphism and encourages neoteny in humans.

Menstrual cycle alters face preference

Women prefer slightly feminized male facial shapes. Such faces (Fig. 1a) are given positive personality attributions that might correlate with actual behaviour. In contrast, masculine features seem to signal immunological competence. Heritable benefits can be realized only if conception follows copulation, so women might be more attentive to phenotypic markers indicating immunological competence during the follicular phase of the menstrual cycle when conception is most likely,. Consistent with this hypothesis is the observation that womens preference for the odour of men with low fluctuating asymmetry (a correlate of testosterone-facilitated trait size and developmental stability) increases with the probability of conception across the menstrual cycle.Symmetrical men report more extra-pair copulation partners, and extra-pair copulation rates peak in midcycle. Here we show that female preference for secondary sexual traits in male face shapes varies with the probability of conception across the menstrual cycle.

Symmetry and human facial attractiveness

Abstract Symmetry may act as a marker of phenotypic and genetic quality and is preferred during mate selection in a variety of species. Measures of human body symmetry correlate with attractiveness, but studies manipulating human face images report a preference for asymmetry. These results may reflect unnatural feature shapes and changes in skin textures introduced by image processing. When the shape of facial features is varied (with skin textures held constant), increasing symmetry of face shape increases ratings of attractiveness for both male and female faces. These findings imply facial symmetry may have a positive impact on mate selection in humans.

Partnership status and the temporal context of relationships influence human female preferences for sexual dimorphism in male face shape

Secondary sexual characteristics may indicate quality of the immune system and therefore a preference for masculinity may confer genetic benefits to offspring; however, high masculinity may be associated with costs of decreased paternal investment. The current study examined womens preferences for masculinity in male faces by using computer graphics to allow transformation between feminine and masculine versions of individual male faces. We found that preferences for masculinity are increased when women either have a partner or are considering a short–term relationship. Such preferences are potentially adaptive, serving to: (i) maximize parental investment and cooperation in long–term relationships by biasing choices towards feminine faced males, and (ii) maximize possible good–gene benefits of short–term or extra–pair partners by biasing choices towards masculine faced males. We also found that individuals using oral contraception do not show the above effects, indicating that such hormonal intervention potentially disrupts womens choices for evolutionarily relevant benefits from males.

Self-perceived attractiveness influences human female preferences for sexual dimorphism and symmetry in male faces

Exaggerated sexual dimorphism and symmetry in human faces have both been linked to potential ‘good–gene’ benefits and have also been found to influence the attractiveness of male faces. The current study explores how female self–rated attractiveness influences male face preference in females using faces manipulated with computer graphics. The study demonstrates that there is a relatively increased preference for masculinity and an increased preference for symmetry for women who regard themselves as attractive. This finding may reflect a condition–dependent mating strategy analogous to behaviours found in other species. The absence of a preference for proposed markers of good genes may be adaptive in women of low mate value to avoid the costs of decreased parental investment from the owners of such characteristics.

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.

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.

Testosterone responses to competition in men are related to facial masculinity

Relationships between androgens and the size of sexually dimorphic male traits have been demonstrated in several non-human species. It is often assumed that a similar relationship exists for human male faces, but clear evidence of an association between circulating testosterone levels and the size of masculine facial traits in adulthood is absent. Here we demonstrate that, after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces. In participants randomly allocated to a ‘winning’ condition, testosterone was elevated relative to pre-task levels at 5 and 20 min post-task. In a control group of participants allocated to a ‘losing’ condition there were no significant differences between pre- and post-task testosterone. An index of facial masculinity based on the measurement of sexually dimorphic facial traits was not associated with pre-task (baseline) testosterone levels, but was associated with testosterone levels 5 and 20 min after success in the competitive task. These findings indicate that a mans facial structure may afford important information about the functioning of his endocrine system.

Investigating an imprinting-like phenomenon in humans Partners and opposite-sex parents have similar hair and eye colour

Research has shown that human partners are more similar than expected by chance on a variety of traits. Studies examining hair and eye colour show some evidence of positive assortment. Positive assortment may reflect attraction to self-similar characteristics but is also consistent with attraction to parental traits. Here, we examine self-reported partner hair and eye colour and the influence that own and parental colour characteristics have on these variables. Parental characteristics were found to correlate positively with actual partner characteristics for both men and women. Regression analysis predicting partner characteristics from maternal and paternal traits (which controls for own traits) revealed the greater importance of the opposite-sex parent over the same-sex parent in predicting both hair and eye colour of actual partners. The findings may reflect an influence of parental colour characteristics on human partner choice. Attraction to opposite-sex parental characteristics is seen in a wide variety of animals where it is usually attributed to imprinting processes in infancy. Although the mechanism is unclear and not necessarily confined to infancy, the data reported here are consistent with a somewhat analogous process to imprinting occurring in humans. D 2002 Elsevier Science Inc. All rights reserved.

Facial attractiveness judgements reflect learning of parental age characteristics

Mate preferences are shaped by infant experience of parental characteristics in a wide variety of species. Similar processes in humans may lead to physical similarity between parents and mates, yet this possibility has received little attention. The age of parents is one salient physical characteristic that offspring may attend to. The current study used computer–graphic faces to examine how preferences for age in faces were influenced by parental age. We found that women born to ‘old’ parents (over 30) were less impressed by youth, and more attracted to age cues in male faces than women with ‘young’ parents (under 30). For men, preferences for female faces were influenced by their mothers age and not their fathers age, but only for long–term relationships. These data indicate that judgements of facial attractiveness in humans reflect the learning of parental characteristics.