Menstrual cycle alters face preference

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.

Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus)

Females alter their mate choices as they transition through different reproductive stages; however, the proximal mechanisms for such behavioral fluctuation are unclear. In many taxa, as females transition through different reproductive stages, there is an associated change in hormone levels; therefore, we examined whether fluctuation in hormone levels serves as a proximal mechanism for within-individual variation in mate choice in female túngara frogs (Physalaemus pustulosus). We manipulated hormone levels of females by administering 0, 10, 100, 500 or 1,000 IU of human chorionic gonadotropin (HCG), which is a ligand for luteinizing hormone (LH) receptors and will therefore cause increased gonadal hormone production. Phonotaxis assays were conducted to measure three aspects of mate choice behavior before and after HCG administration; receptivity (response to a conspecific mate signal), permissiveness (response to a signal that is less attractive than conspecific signals) and discrimination (ability to discern signal differences). The probability of response to a conspecific and an artificial hybrid signal significantly increased at the highest HCG doses. The difference in mean response time between pre- and post-HCG tests was significantly different for both the receptivity and permissiveness tests among the five doses. Increased permissiveness, however, was not due to decreased discrimination because females could discriminate between calls even at the highest HCG doses. These hormonal manipulations caused the same behavioral pattern we reported in females as they transitioned through different reproductive stages (Lynch, K.S., Rand, A.S., Ryan, M.J., Wilczynski, W., 2005. Plasticity in female mate choice associated with changing reproductive states. Anim. Behav. 69, 689-699), suggesting that changes in hormone levels can influence the female's mate choice behavior.

Conditional expression of women's desires and men's mate guarding across the ovulatory cycle

Thirty-eight normally cycling women provided daily reports of sexual interests and feelings for 35 days. Near ovulation, both pair-bonded and single women reported feeling more physically attractive and having greater interest in attending social gatherings where they might meet men. Pair-bonded women who were near ovulation reported greater extra-pair flirtation and greater mate guarding by their primary partner. As predicted, however, these effects were exhibited primarily by women who perceived their partners to be low on hypothesized good genes indicators (low in sexual attractiveness relative to investment attractiveness). Ovulation-contingent increases in partner mate guarding were also moderated by female physical attractiveness; midcycle increases in mate guarding were experienced primarily by less attractive women, whereas more attractive women experienced relatively high levels of mate guarding throughout their cycle. These findings demonstrate ovulation-contingent shifts in desires and behaviors that are sensitive to varying fitness payoffs, and they provide support for the good genes hypothesis of human female extra-pair mating. The daily assessment method provides an important supplement to existing studies using scheduled laboratory visits as the purpose of the study (examining cycle-related variation) is not known by participants.

Estrogen-dependent selectivity of genomic responses to birdsong

Behavioral responses to sociosexual signals often depend on gonadal steroid hormones, which are thought to modulate behavior by acting on motivational systems in the brain. There is mounting evidence that sex steroids may also modulate perception of sociosexual signals by affecting sensory processing. In seasonally breeding songbirds such as the white-throated sparrow (Zonotrichia albicollis), the female's behavioral response to hearing male song depends on her plasma levels of estradiol (E2). Here, we examined whether plasma E2 also affects the selectivity of the song-induced zenk (egr-1) response in the auditory forebrain, which is known to vary according to the behavioral relevance of song stimuli. Non-breeding females were held on a winter-like photoperiod and implanted with silastic capsules containing either no hormone or E2. E2-treated birds hearing 42 min of conspecific song had more cells immunoreactive for the protein product of zenk in the auditory forebrain than did those hearing frequency-matched synthetic tones. In birds not treated with E2, however, the zenk response to song did not differ from that to tones. We found similar effects in the avian homolog of the inferior colliculus, indicating that E2 may affect the processing of auditory information upstream of the forebrain. Our data suggest that in females, zenk induction in the auditory system is selective for song only when plasma E2 exceeds non-breeding levels. E2-dependent plasticity of auditory pathways and processing centres may promote recognition of and attention to conspecific song during the breeding season.

Mate choice decisions: the role of facial beauty

For most people, facial beauty appears to play a prominent role in choosing a mate. Evidence from research on facial attractiveness indicates that physical beauty is a sexually selected trait mediated, in part, by pubertal facial hormone markers that signal important biological information about the displayer. Such signals would be ineffective if they did not elicit appropriate cognitive and/or emotional responses in members of the opposite sex. In this article, I argue that the effectiveness of these hormonal displays varies with perceivers' brains, which have been organized by the degree of steroid hormone exposure in the uterus, and activated by varying levels of circulating steroids following puberty. I further propose that the methodology used for examining mate choice decisions has general applicability for determining how cognitive and emotional evaluations enter into decision processes.

The Evolutionary Psychology of Facial Beauty

What makes a face attractive and why do we have the preferences we do? Emergence of preferences early in development and cross-cultural agreement on attractiveness challenge a long-held view that our preferences reflect arbitrary standards of beauty set by cultures. Averageness, symmetry, and sexual dimorphism are good candidates for biologically based standards of beauty. A critical review and meta-analyses indicate that all three are attractive in both male and female faces and across cultures. Theorists have proposed that face preferences may be adaptations for mate choice because attractive traits signal important aspects of mate quality, such as health. Others have argued that they may simply be by-products of the way brains process information. Although often presented as alternatives, I argue that both kinds of selection pressures may have shaped our perceptions of facial beauty.

THE EVOLUTION OF HUMAN PHYSICAL ATTRACTIVENESS

Everywhere the issue has been examined, people make discriminations about others’ physical attractiveness. Can human standards of physical attractiveness be understood through the lens of evolutionary biology? In the past decade, this question has guided much theoretical and empirical work. In this paper, we (a) outline the basic adaptationist approach that has guided the bulk of this work, (b) describe evolutionary models of signaling that have been applied to understand human physical attractiveness, and (c) discuss and evaluate specific lines of empirical research attempting to address the selective history of human standards of physical attractiveness. We also discuss ways evolutionary scientists have attempted to understand variability in standards of attractiveness across cultures as well as the ways current literature speaks to body modification in modern Western cultures. Though much work has been done, many fundamental questions remain unanswered.

Women's preference for dominant male odour: effects of menstrual cycle and relationship status

Body odour may provide significant cues about a potential sexual partner's genetic quality, reproductive status and health. In animals, a key trait in a female's choice of sexual partner is male dominance but, to date, this has not been examined in humans. Here, we show that women in the fertile phase of their cycle prefer body odour of males who score high on a questionnaire-based dominance scale (international personality items pool). In accordance with the theory of mixed mating strategies, this preference varies with relationship status, being much stronger in fertile women in stable relationships than in fertile single women.

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 women's behavior during the menstrual cycle have offered insight into the motivations underpinning women's 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 women's preferences for male and female faces and in their attitudes to their romantic relationship during the menstrual cycle. In Study 1, we found partnered women's 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 women's 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 women's 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.

Oral contraceptive use and female genital arousal: methodological considerations

This study explored effects of oral contraceptive pill (OCP) use on physiological sexual arousal as measured by a vaginal photoplethysmograph. Sixteen women aged 18-29 viewed audiovisual neutral and erotic stimuli before and an average of 6 weeks following the onset of OCP use. Although subjective measures of sexual arousal, including perceptions of genital arousal, significantly increased in response to erotic stimuli both before and after OCP onset, physiological sexual arousal only increased before OCP use. A comparison of individual responses before and after OCP onset reveals a much higher degree of intrasubject variability after OCP onset. We discuss these findings as they relate to OCP use as a confounding methodological variable to consider in future investigations employing vaginal photoplethysmography.

A comparative assessment of the perception of Chinese facial profile esthetics

INTRODUCTION

The aim of this study was to compare the perception of male and female Chinese facial profile esthetics between dental professionals, dental students, and laypersons.

MATERIAL

The sample comprised 31 dental professionals (20 orthodontists, 11 oral surgeons), 92 dental students, and 152 laypersons in an Asian community. The facial profile photographs and lateral cephalometric radiographs of a Chinese man and a woman, each with a normal profile, a Class I incisor relationship, and a Class I skeletal pattern, were digitized. The digital images were modified to obtain 7 facial profiles for each sex. The images were constructed by altering cephalometric skeletal and dental hard tissue Chinese normative values by 2 standard deviations in the anteroposterior plane only. The 7 profiles were (1) bimaxillary protrusion, (2) protrusive mandible, (3) retrusive mandible, (4) normal profile (Class I incisor with Class I skeletal pattern), (5) retrusive maxilla, (6) protrusive maxilla, and (7) bimaxillary retrusion.

RESULTS

Normal and bimaxillary retrusion Chinese male and female profiles were perceived to be highly attractive by all 3 groups. Profiles with a protrusive mandible were perceived to be the least attractive. Dental professionals, dental students, and laypersons were highly correlated for the perception of male (r > 0.67) and female (r > 0.93) profile esthetics. All correlation coefficients were found to be significant for the perception of female profiles, but, for male profiles, only the correlation coefficient between dental students and laypersons was significant.

CONCLUSIONS

Chinese male and female profiles that were normal or had bimaxillary retrusion were perceived to be highly attractive by dental professionals, dental students, and laypersons, and profiles with a protrusive mandible were perceived to be the least attractive. Dental students and laypersons were more tolerant of a male profile with a retrusive mandible than were dental professionals, and all groups were more tolerant of bimaxillary protrusion in women than in men. Dental professionals, dental students, and laypersons had a similar trend in male and female esthetic preferences. The perception of female profiles by all 3 groups was highly and significantly correlated. Only the perception of male esthetics by dental students and laypersons was not significantly correlated with dental professionals.

Wide faces or large canines? The attractive versus the aggressive primate

Hominids display marked body size dimorphism, suggestive of strong sexual selection, yet they lack significant sex differences in canine size that are commonly associated with intrasexual competition in primates. We resolve this paradox by examining sex differences in hominoid facial morphology. We show that chimpanzees, but not gorillas, exhibit clear sexual dimorphism in face width, over and above that expected based on sex differences in body size. We show that this facial dimorphism, expressed as an index, is negatively correlated with canine dimorphism among anthropoid primates. Our findings suggest that a lack of canine dimorphism in anthropoids is not owing to weak sexual selection, but rather is associated with strong sexual selection for broader face width. Enlarged cheek-bones are linked with attractiveness in humans, and we propose that the evolution of a broad face and loss of large canines in hominid males results from mate choice.

Menstrual cycle, pregnancy and oral contraceptive use alter attraction to apparent health in faces

Previous studies demonstrating changes in women's face preferences have emphasized increased attraction to cues to possible indirect benefits (e.g. heritable immunity to infection) that coincides with periods of high fertility (e.g. the late follicular phase of the menstrual cycle). By contrast, here we show that when choosing between composite faces with raised or lowered apparent health, women's preferences for faces that are perceived as healthy are (i) stronger during the luteal phase of the menstrual cycle than during the late follicular, fertile phase, (ii) stronger in pregnant women than in non-pregnant women and (iii) stronger in women using oral contraceptives than in women with natural menstrual cycles. Change in preference for male faces was greater for short- than long-term relationships. These findings indicate raised progesterone level is associated with increased attraction to facial cues associated with possible direct benefits (e.g. low risk of infection) and suggest that women's face preferences are influenced by adaptations that compensate for weakened immune system responses during pregnancy and reduce the risk of infection disrupting foetal development.

Male reproductive physiology as a sexually selected handicap? Erectile dysfunction is correlated with general health and health prognosis and may have evolved as a marker of poor phenotypic quality

Many extravagant physical traits are selected because they are used as cues for mate choice (sexual selection). Why is mate choice driven by costly ornaments? A theory of sexual selection posits that extravagant traits are preferred because are reliable indicators of superior (heritable) phenotypic quality. In particular, the preferred traits can be expressed only in individuals with superior conditions because are handicaps which impose a high cost to the carrier. The human penis achieves its reproductive function by the complex neuro-vascular mechanisms that controls erection. Surprisingly, erectile dysfunction and infertility, two condition which nearly annihilate fitness, are widespread medical conditions which affect millions of people of any age worldwide. The very high incidence of erectile dysfunction appears as an evolutionary paradox. Impotence is associated with all major systemic diseases as well depression and stress. Stress is also one of the causes of infertility. Therefore, male reproduction appears to be extremely sensitive to internal and external stressors. Moreover, erectile dysfunction is a predictor of myocardial infarction and stroke, whereas men with regular sexual activity have lower risk of death due to coronary disease. This large body of medical literature makes erection the best case for a fitness indicator in the human male. We suggest that the fragility of male sexual physiology observed in modern society is the specific consequence of an evolutionary process driven by the handicap principle.

Female intrasexual competition decreases female facial attractiveness

Evolutionary theory predicts that female intrasexual competition will occur when males of high genetic quality are considered to be a resource. It is probable that women compete in terms of attractiveness since this is one of the primary criteria used by men when selecting mates. Furthermore, because hormones influence the mate-selection process, they may also mediate competition. One competitive strategy that women use is derogation--any act intended to decrease a rival's perceived value. To investigate intrasexual competition through derogation, the influence of oestrogen on women's ratings of female facial attractiveness was examined. During periods of high oestrogen, competition, and hence derogation, increased, as evidenced by lower ratings of female facial attractiveness. By contrast, oestrogen levels did not significantly affect ratings of male faces. These findings support the theory of female intrasexual competition with respect to attractiveness.

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 women's 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 female's relative value in the mating market at the time in the cycle when the probability of conception is at its highest.

Facial resemblance increases the attractiveness of same-sex faces more than other-sex faces

Our reactions to facial self-resemblance could reflect either specialized responses to cues of kinship or by-products of the general perceptual mechanisms of face encoding and mere exposure. The adaptive hypothesis predicts differences in reactions to self-resemblance in mating and prosocial contexts, while the by-product hypothesis does not. Using face images that were digitally transformed to resemble participants, I showed that the effects of resemblance on attractiveness judgements depended on both the sex of the judge and the sex of the face being judged: facial resemblance increased attractiveness judgements of same-sex faces more than other-sex faces, despite the use of identical procedures to manipulate resemblance. A control experiment indicated these effects were caused neither by lower resemblance of other-sex faces than same-sex faces, nor by an increased perception of averageness or familiarity of same-sex faces due to prototyping or mere exposure affecting only same-sex faces. The differential impact of self-resemblance on our perception of same-sex and other-sex faces supports the hypothesis that humans use facial resemblance as a cue of kinship.

Altering first impressions after facial plastic surgery

BACKGROUND

First impressions are greatly influenced by facial appearance. Clinical data from psychiatric medicine overwhelming indicate that attractive individuals receive better judgment, treatment and behavior [1,2,10]. This study aimed to determine whether cosmetic alteration of facial features projects a better first impression.

METHODS

Random reviewers were asked independently to grade standardized preoperative and postoperative photographs of patients who underwent facial plastic surgery. The reviewers were blinded to the pre- or postoperative status of the photograph. The questions posed to the reviewers were based on first-impression studies used in the past.

RESULTS

The findings indicate that postoperative cosmetic surgery patients were graded as 31% more attractive, 27% better in social skills, 22% more successful in dating, 19% better in athletic skills, 15% better in relationship skills, and 13% more financially successful.

CONCLUSION

Facial cosmetic surgery can improve the first impression an individual creates.

Schizophrenia as one extreme of a sexually selected fitness indicator

Schizophrenia remains an evolutionary paradox. Its delusions, hallucinations and other symptoms begin in adolescence or early adulthood and so devastate sexual relationships and reproductive success that selection should have eliminated the disorder long ago. Yet it persists as a moderately heritable disorder at a global 1% prevalence--too high for new mutations at a few genetic loci. We suggest that schizophrenia persists and involves many loci because it is the unattractive, low-fitness extreme of a highly variable mental trait that evolved as a fitness ("good genes") indicator through mutual mate choice. Here we show that this hypothesis explains many key features of schizophrenia and predicts that some families carry modifier alleles that increase the indicator's neurodevelopmental sensitivity to heritable fitness and condition. Such alleles increase the extent to which high-fitness family members develop impressive courtship abilities and achieve high reproductive success, but also increase the extent to which low-fitness family members develop schizophrenia. Here we introduce this fitness indicator model of schizophrenia, discuss its explanatory power, explain how it resolves the evolutionary paradox, discuss its implications for gene hunting, and identify some empirically testable predictions as directions for further research.

Sex differences in judgments of physical attractiveness: a social relations analysis

Men and women rated the physical attractiveness of other men and women who were sitting nearby and were rated by them in return. They also provided meta-perceptions of how they thought those others rated them. Attractiveness ratings were partly a function of both the target being rated and the perceiver providing the ratings regardless of the sex of the perceiver or target, but the highest levels of consensus occurred when men judged the attractiveness of women and the highest levels of idiosyncrasy occurred when men rated other men. Meta-perceptions were also idiosyncratic; some believed that they were consistently considered attractive, whereas others thought they were seen as unattractive. People were aware of what others thought of them and, in particular, women's meta-perceptions were highly related to men's judgments of them. People agree about others' attractiveness, and those who are attractive to others know they are pretty or handsome.

Concordant preferences for opposite-sex signals? Human pheromones and facial characteristics

We have investigated whether preferences for masculine and feminine characteristics are correlated across two modalities, olfaction and vision. In study 1, subjects rated the pleasantness of putative male (4,16-androstadien-3-one; 5alpha-androst-16-en-3-one) and female (1,3,5 (10),16-estratetraen-3-ol) pheromones, and chose the most attractive face shape from a masculine-feminine continuum for a long- and a short-term relationship. Study 2 replicated study 1 and further explored the effects of relationship context on pheromone ratings. For long-term relationships, women's preferences for masculine face shapes correlated with ratings of 4,16-androstadien-3-one and men's preferences for feminine face shapes correlated with ratings of 1,3,5(10),16-estratetraen-3-ol. These studies link sex-specific preferences for putative human sex pheromones and sexually dimorphic facial characteristics. Our findings suggest that putative sex pheromones and sexually dimorphic facial characteristics convey common information about the quality of potential mates.

Smelling human sex hormone-like compounds affects face gender judgment of men

Although strong cross-sensory interactions between visual, tactile and auditory modalities have already been shown, we know little about how chemosensory information affects processing in other sensory modalities. We studied whether smelling gender-specific odorous sex hormone-like steroids: 5-alpha-androgenst-16-en-3-one (androgen) or oestra-1, 3, 5 (10), 16-tetraen-3-ol (estrogen) can bias face gender discrimination. We found that, as a result of inhalation of androgen, men perceive faces to be more masculine as compared to when they are exposed to estrogen. Our results provide evidence for specific cross-sensory effects of the gender-specific chemosensory cues on the categorization of visual face gender.

Between nurture and nature: the shifting determinants of female fertility in Danish twin cohorts

Behaviors related to fertility constitute primary candidates for investigating the relevance of evolutionary influences and biological dispositions on contemporary human behaviors. Using female Danish twin cohorts born 1870-1968, we document important transformations in the relative contributions of "nurture" and "nature" to within-cohort variations in early and complete fertility, and we point toward a systematic relation between the socioeconomic context of cohorts and the relevance of genetic and shared environmental factors. This transformation is most striking for early fertility where genetic factors strengthen over time and are consistent with up to 50 percent of the variation in early fertility in most recent cohorts. Understanding this emerging relevance of genetic factors is of central importance because early fertility constitutes an important determinant of complete fertility levels in low-fertility societies, and because teenage motherhood and early childbearing are often associated with negative life-cycle consequences. Moreover, our results emphasize the need for socially and contextually informed analyses of nature and nurture that allow both factors to influence human reproductive behavior over time.

Female condition influences preferences for sexual dimorphism in faces of male humans (Homo sapiens)

In some species, female condition correlates positively with preferences for male secondary sexual traits. Women's preferences for sexually dimorphic characteristics in male faces (facial masculinity) have recently been reported to covary with self-reported attractiveness. As women's attractiveness has been proposed to signal reproductive condition, the findings in human (Homo sapiens) and other species may reflect similar processes. The current study investigated whether the covariation between condition and preferences for masculinity would generalize to 2 further measures of female attractiveness: other-rated facial attractiveness and waist-to-hip ratio (WHR). Women with high (unattractive) WHR and/or relatively low other-rated facial attractiveness preferred more "feminine" male faces when choosing faces for a long-term relationship than when choosing for a short-term relationship, possibly reflecting diverse tactics in female mate choice.

Sex-differential brain activation during exposure to female and male faces

Sex-discriminating facial features are examples of visual information involved in guiding social behavior. We used functional magnetic resonance imaging (fMRI) to assess brain responses in face-relevant brain areas in men and women during exposure to neutral male and female faces. An increased fMRI signal was found in the left amygdala and adjacent anterior temporal regions in men, but not in women, during exposure to faces of the opposite versus the same sex. These data indicate that the relationship between the sex of the subject and the sex of the face affects activity in the inferior temporal lobe. The sex-differential nature of this activation pattern may reflect sex differences in cognitive style and attentional processes when confronting faces of the opposite sex.

Evolution of human mate choice

This article provides a review of evolutionary theory and empirical research on mate choices in nonhuman species and uses it as a frame for understanding the how and why of human mate choices. The basic principle is that the preferred mate choices and attendant social cognitions and behaviors of both women and men, and those of other species, have evolved to focus on and exploit the reproductive potential and reproductive investment of members of the opposite sex. Reproductive potential is defined as the genetic, material, and/or social resources an individual can invest in offspring, and reproductive investment is the actual use of these resources to enhance the physical and social well- being of offspring. Similarities and differences in the mate preferences and choices of women and men are reviewed and can be understood in terms of similarities and differences in the form of reproductive potential that women and men have to offer and their tendency to use this potential for the well-being of children.

Disco clothing, female sexual motivation, and relationship status: is she dressed to impress?

The relationship between a female's clothing choice, sexual motivation, hormone levels, and partnership status (single or not single, partner present or not present) was analyzed in 351 females attending Austrian discotheques. We digitally analyzed clothing choice to determine the amount of skin display, sheerness, and clothing tightness. Participants self-reported sexual motivation, and we assessed estradiol and testosterone levels through saliva sampling. Results show that females are aware of the social signal function of their clothing and that they in some cases alter their clothing style to match their courtship motivation. In particular, sheer clothing -although rare in the study- positively correlated with the motivation for sex. Hormone levels influenced clothing choice in many groups, with testosterone levels correlating positively with physique display. In females who had a partner but were at the disco unaccompanied by the partner, estradiol levels correlated positively with skin display and clothing tightness. Significant differences were not found, however, for clothing choice across the partnership-status groups.

Ovulatory shifts in female sexual desire

Women's reproductive biology imposes heavy obligatory costs of parental investment, creating strong selective forces hypothesized to shape female mating psychology around critical decisions such as the choice of partner, the timing of sexual intercourse, and the timing of reproduction. We propose that female sexual desire has evolved as one adaptation among several designed to regulate these decisions. We hypothesize (a) an increase in desire as conception probability increases, but only among women who are in committed long-term relationships; and (b) a shift in the desire for a primary partner as compared with extra-pair partners as ovulation approaches, dependent upon a woman's evaluation of her primary partner's relative quality. We tested several predictions derived from these hypotheses in a study of 173 women who were not taking oral contraceptives. Results confirmed Hypothesis 1: An ovulatory peak in sexual desire was found only for mated women; for unmated women, conception probability and sexual desire were uncorrelated. Hypothesis 2 was partially supported. Among mated women, those with higher conception probability exhibited higher levels of in-pair sexual desire relative to those at lower conception probability. Conception probability and relationship length interacted significantly to predict extra-pair desires, such that women in longer relationships were more likely to experience desire for extra-pair partners during periods of high conception probability. The pursuit of an in-pair conceptive strategy (as opposed to an extra-pair conceptive strategy) was also associated with the occurrence of sexual activity in the relationship.

Narcissism Guides Mate Selection: Humans Mate Assortatively, as Revealed by Facial Resemblance, following an Algorithm of “Self Seeking Like”

Theoretical studies suggest that mating and pair formation is not likely to be random. Computer simulations suggested that sex among genetically complex organisms requires mate choice strategies for its evolutionary maintenance, to reduce excessive genetic variance produced by out-crossing. One strategy achieving this aim efficiently in computer simulations is assortative mating modeled as “self seeking like”. Another one is selection of “good genes”. Assortative mating increases the probability of finding a genetically similar mate, without fomenting inbreeding, achieving assortative mating without hindering the working of other mate selection strategies which aim to maximize the search for “good genes”, optimizing the working of sex in evolutionary terms. Here we present indirect evidence that in a significant proportion of human reproductive couples, the partners show much higher facial resemblances than can be expected by random pair formation, or as the outcome of “matching for attractiveness” or the outcome of competition for the most attractive partner accessible, as had been previously assumed. The data presented is compatible with the hypothesis derived from computer simulations, that human mate selection strategies achieve various aims: “self seeking like” (including matching for attractiveness) and mating with the best available genes.

Darwinian aesthetics: sexual selection and the biology of beauty

Current theoretical and empirical findings suggest that mate preferences are mainly cued on visual, vocal and chemical cues that reveal health including developmental health. Beautiful and irresistible features have evolved numerous times in plants and animals due to sexual selection, and such preferences and beauty standards provide evidence for the claim that human beauty and obsession with bodily beauty are mirrored in analogous traits and tendencies throughout the plant and animal kingdoms. Human beauty standards reflect our evolutionary distant and recent past and emphasize the role of health assessment in mate choice as reflected by analyses of the attractiveness of visual characters of the face and the body, but also of vocal and olfactory signals. Although beauty standards may vary between cultures and between times, we show in this review that the underlying selection pressures, which shaped the standards, are the same. Moreover we show that it is not the content of the standards that show evidence of convergence--it is the rules or how we construct beauty ideals that have universalities across cultures. These findings have implications for medical, social and biological sciences.

Does sexual dimorphism in human faces signal health?

Evolutionary psychologists suggest that a preference for sexually dimorphic traits in human faces is an adaptation for mate choice, because such traits reflect health during development. For male faces, this claim rests on the immunocompetence-handicap hypothesis, which states that the increased testosterone levels needed to develop large masculine traits stress the immune system. We examined whether masculine traits in adolescent male faces are associated with health during development, and also whether feminine traits in adolescent female faces signal health. Feminine traits are attractive, but it is less clear whether they should signal health. Rated masculinity in adolescent male faces correlated modestly with actual health, and was perceived as healthy, but not as attractive. Rated femininity in adolescent female faces did not correlate with actual health, although it was perceived as healthy and attractive. These results support the immunocompetence-handicap hypothesis for male faces in that masculine traits signalled health during adolescence. However, they suggest that any health-related evolutionary benefits obtained from preferences for attractive facial traits may be weak.