Facial attractiveness signals different aspects of “quality” in women and men

We explored the relationships between facial attractiveness and several variables thought to be related to genotypic and phenotypic quality in humans (namely fluctuating asymmetry (FA), body mass index (BMI), health, age). To help resolve some controversy around previous studies, we used consistent measurement and statistical methods and relatively large samples of both female (n=94) and male (n=95) subjects (to be evaluated and measured), and female (n=226) and male (n=153) viewers (to rate attractiveness). We measured the asymmetry of 22 traits from three trait families (eight facial, nine body and five fingerprint traits) and constructed composite asymmetry indices of traits showing significant repeatability. Facial attractiveness was negatively related to an overall asymmetry index in both females and males, with almost identical slopes. Female facial attractiveness was best predicted by BMI and past health problems, whereas male facial attractiveness was best predicted by the socioeconomic status (SES) of their rearing environment. Composite FA indices accounted for a small (<4%) but usually significant percentage of the variation in facial attractiveness in both sexes, when factors related to asymmetry were controlled statistically. We conclude that, although facial attractiveness is negatively related to developmental instability (as measured by asymmetry), attractiveness also signals different aspects of “quality” in the two sexes, independent of FA.     

Do facial averageness and symmetry signal health?

We investigated whether the attractive facial traits of averageness and symmetry signal health, examining two aspects of signalling: whether these traits are perceived as healthy, and whether they provide accurate health information. In Study 1, we used morphing techniques to alter the averageness and symmetry of individual faces. Increases in both traits increased perceived health, and perceived health correlated negatively with rated distinctiveness (a converse measure of averageness) and positively with rated symmetry of the images. In Study 2, we examined whether these traits signal real, as well as perceived, health, in a sample of individuals for whom health scores, based on detailed medical records, were available. Perceived health correlated negatively with distinctiveness and asymmetry, replicating Study 1. Facial distinctiveness ratings of 17-year-olds were associated with poor childhood health in males, and poor current and adolescent health in females, although the last association was only marginally significant. Facial asymmetry of 17-year-olds was not associated with actual health. We discuss the implications of these results for a good genes account of facial preferences.     

Symmetry of the face in old age reflects childhood social status

The association of socioeconomic status (SES) with a range of lifecourse outcomes is robust, but the causes of these associations are not well understood. Research on the developmental origins of health and disease has led to the hypothesis that early developmental disturbance might permanently affect the lifecourse, accounting for some of the burden of chronic diseases such as coronary heart disease. Here we assessed developmental disturbance using bodily and facial symmetry and examined its association with socioeconomic status (SES) in childhood, and attained status at midlife. Symmetry was measured at ages 83 (facial symmetry) and 87 (bodily symmetry) in a sample of 292 individuals from the Lothian Birth Cohort 1921 (LBC1921). Structural equation models indicated that poorer SES during early development was significantly associated with lower facial symmetry (standardized path coefficient ?.25, p = .03). By contrast, midlife SES was not significantly associated with symmetry. The relationship was stronger in men (?.44, p = .03) than in women (?.12, p = .37), and the effect sizes were significantly different in magnitude (p = .004). These findings suggest that SES in early life (but not later in life) is associated with developmental disturbances. Facial symmetry appears to provide an effective record of early perturbations, whereas bodily symmetry seems relatively imperturbable. As bodily and facial symmetries were sensitive to different influences, they should not be treated as interchangeable. However, markers of childhood disturbance remain many decades later, suggesting that early development may account in part for associations between SES and health through the lifecourse. Future research should clarify which elements of the environment cause these perturbations.     

Facial sexual dimorphism,developmental stability,and susceptibility to disease in men and women

We investigated aspects of self-reported health history–the number and duration of respiratory and stomach or intestinal infections and the number of uses of antibiotics over the last 3 years–in relation to measured facial masculinity, developmental instability [facial asymmetry and body fluctuating asymmetry (FA)] and facial attractiveness in a sample of 203 men and 203 women. As predicted from the hypothesis that the degree of facial masculinity is an honest signal of individual quality, men's facial masculinity correlated negatively and women's positively with respiratory disease number and duration. Stomach illness, however, was not associated significantly with facial masculinity and antibiotic use correlated significantly (negatively) only with men's facial masculinity. For both facial asymmetry and body FA, significant, positive associations were seen with the number of respiratory infections. In addition, facial asymmetry was associated positively with the number of days infected and marginally, in the same direction, with antibiotic use. Facial attractiveness showed no significant relationships with any of our health-history measures. This study provides some evidence that facial masculinity in both sexes may signal disease resistance and that developmental stability covaries positively with disease resistance. The validity of our health measures is discussed.     

Developmental changes in children's facial preferences

Facial averageness, symmetry, health, and femininity are positively associated with adults' judgements of attractiveness, but little is known about the age at which preferences for individual facial traits develop. We investigated preferences for these facial traits and global attractiveness in 4- to 17-year-olds (N = 346). All age groups showed preferences for globally attractive faces. Preferences for averageness, symmetry, and health did not emerge until middle childhood and experienced apparent disruption or stasis around age 10- to 14-years; femininity was not preferred until early adulthood, and this preference was seen only in girls. Children's pubertal development was not clearly related to any facial preferences, but the results are consistent with the suggestion that early adrenal hormone release may play an activating role in mate preferences, while other constraints may delay further increases in preferences during later puberty.     

Chimpanzee facial symmetry: a biometric measure of chimpanzee health

This paper reports a study of fitness indicator theory in chimpanzees. First, it establishes a theoretical perspective for the study of fitness indicator theory and the relationships among indicators of fitness in humans and other animals. Second, it describes a methodology for assessing facial fluctuating asymmetry (FA) in a sample (N = 21) of zoo chimpanzees (Pan troglodytes). Third, associations among chimpanzee facial FA and health are described. FA was positively associated with negative health symptoms, and negatively associated with general health. Results are discussed under the framework of good genes theory.     

Are there vocal cues to human developmental stability? Relationships between facial fluctuating asymmetry and voice attractiveness

Fluctuating asymmetry (FA), deviation from perfect bilateral symmetry, is thought to reflect an organism's relative inability to maintain stable morphological development in the face of environmental and genetic stressors. Previous research has documented negative relationships between FA and attractiveness judgments in humans, but scant research has explored relationships between the human voice and this putative marker of genetic quality in either sex. Only one study (and in women only) has explored relationships between vocal attractiveness and asymmetry of the face, a feature-rich trait space central in prior work on human genetic quality and mate choice. We therefore examined this relationship in three studies comprising 231 men and 240 women from two Western samples as well as Hadza hunter–gatherers of Tanzania. Voice recordings were collected and rated for attractiveness, and FA was computed from two-dimensional facial images as well as, for a subset of men, three-dimensional facial scans. Through meta-analysis of our results and those of prior studies, we found a negative association between FA and vocal attractiveness that was highly robust and statistically significant whether we included effect sizes from previously published work, or only those from the present research, and regardless of the inclusion of any individual sample or method of assessing FA (e.g., facial or limb FA). Weighted mean correlations between FA and vocal attractiveness across studies were ?.23 for men and ?.29 for women. This research thus offers strong support for the hypothesis that voices provide cues to genetic quality in humans.     

The relationship between sexual dimorphism in human faces and fluctuating asymmetry

Previous studies have found both support and lack of support for a positive relationship between masculinity and symmetry, two putative signs of mate quality, in male faces. We re-examined this relationship using an explicit measure of facial fluctuating asymmetry, as well as other measures of asymmetry, and measures of facial masculinity/femininity. We also used ratings of these traits for faces. Further, we examined the relationship between facial sexual dimorphism and body asymmetry. We found no significant correlations between facial masculinity and any of our measures of asymmetry or ratings of symmetry in males. Facial femininity was not consistently associated with facial symmetry in females, but was associated with body symmetry. Therefore, for females, but not males, facial femininity and body symmetry may reflect similar aspects of mate quality. We also examined the relationships between trait ratings and measurements. Our results provide validation of our ability to measure aspects of asymmetry that are perceived to be symmetrical, and aspects of sexual dimorphism that are perceived as feminine in females and masculine in males.     

Developmental stability in yellow dung flies (Scathophaga stercoraria): fluctuating asymmetry,heterozygosity and environmental stress

The genetic basis for developmental stability, the ability of an organism to withstand genetic and environmental disturbance of development, is poorly understood. Fluctuating asymmetry (FA: small random deviations from symmetry in paired, bilateral traits) is the most widely used measure of developmental stability, and evidence suggests FA is weakly and negatively associated with genome‐wide heterozygosity. We investigated the genetic basis of developmental stability in the yellow dung fly. Fly lines were inbred for 16 generations at which time they were homozygous at the phosphoglucomutase (PGM) loci and PGM appears to influence FA in at least one other taxon. After 16 generations of inbreeding, lines homozygous for different PGM alleles were crossed and levels of FA for four metric traits were compared in the inbred and crossed flies. We also compared FA levels in these flies with previously gathered data on wild‐type (second generation outcrossed) flies, and additionally looked at the effects of two environmental stresses (larval food limitation and increased temperature) on FA. There were no significant differences in any measure of FA, nor in mean FA, in any trait when inbred and crossed flies were compared. Comparison of FA in these and wild flies also revealed no significant differences. Food limitation had no influence on FA, whereas heat stress increased FA of naturally, but not sexually, selected traits. Our results do not show a negative relationship between heterozygosity and FA, but support the notion that FA levels are stress, trait and taxon specific.     

The influence of shape and colour cue classes on facial health perception

Facial appearance signals information about an individual, and one trait in particular is vitally important for social interaction and mate choice decisions: physical health. Facial cues to health can be divided into two broad classes - facial shape, which is linked to previous health and is relatively fixed; and facial colouration, which changes over the short-term, reflecting current health. These cue classes in themselves give insight into the kinds of health condition valued by human observers when making social inferences. Here, using novel and generalizable methods, the influence of these cue classes on health perception and their link to a measure of general health are examined. Study One employs a Brunswik lens model approach, finding that observers utilise exclusively shape cues to judge health, and that of these shape cues, only averageness is related to a measure of self-reported general health. Study Two shows that when averageness and carotenoid colouration are varied together, both make separable contributions to perceived health, but that averageness explains a larger proportion of variance. Taken together, these results indicate that humans may have evolved to favour cues to previous condition when judging health, because they are more valid. However, the findings also suggest that the role of facial appearance in perceiving health is more complex than previously thought, with different cues potentially reflecting specific aspects of physiological health.     

Fluctuating asymmetry: A tool for impact assessment on fish populations in a tropical polluted bay,Brazil

Fluctuating asymmetry (FA), which can be defined as random morphologic changes on bilateral symmetry plan of paired morphometric and meristic characters in response of environmental disturbances, is an alternative tool to traditional methods of environmental health assessment that has an interesting potential to appraise the state of adaptation of a population before that acute contaminations affect the whole community or ecosystem. This study aimed to assess the occurrence of FA in three morphometric and three meristic characters of the Corocoro grunt Orthopristis ruber (Cuvier, 1830), and compare the deviations in bilateral symmetry of this reef-associated and omnivorous in Guanabara Bay (Brazil), the venue for various outdoor aquatic sports during the 2016 Olympic Games. Five indexes of FA were tested over the six characters of 66 O. ruber, which were caught during the dry and wet seasons of 2011 and at three areas Guanabara Bay of different environmental characteristics. In addition to validate the existence of FA for O. ruber, our findings revealed significant deviations in the bilateral symmetry according to the FA indexes and fish characters. Together with the FA1 index, the number of gill rakers and the number of rays of the pectoral fin provided the best methodological approach to address the levels of FA in O. ruber as a response to environmental stressors in each region. The levels of FA in O. ruber was significantly lower in the Urca region (less impacted) than for individuals caught near the Paquetá Island and Rio-Niterói Bridge sites (more degraded). Partial Redundancy Analysis also shows that the fish characters are affected in different ways by environmental stressors, but especially in response to the levels of dissolved oxygen and, secondarily, to water transparency, and that Paquetá Island is apparently less impacted than the site near the Rio-Niterói Bridge. Our results confirm the potential of FA to be used as a tool to detect environmental effects on a reef-associated fish species in a tropical polluted bay, but further studies are necessary to validate our findings for other species and ecosystems.     

Is the number of possible QTL for asymmetry phenotypes dependent on thermal stress?

In bilateral organisms, fluctuating asymmetry (FA) was often used as an index of developmental instability but FA was not always found to be higher in stressful environments. An intercontinental set of recombinant inbred lines (RIL) was used to search for genetic variation in fluctuating asymmetry (FA) of both wing length (WL) and wing width (WW) in Drosophila melanogaster when reared at both benign (25 °C) and stressful (30 °C) temperatures. FA levels did not differ between benign and stressful temperatures. At benign temperature, no QTL was significant for FA. However, at stressful temperature, composite interval mapping revealed some QTL for FA in both WL and WW. QTL-based scans under stressful thermal environments may be an informative approach for either FA or developmental instability analyses, even when FA levels are similar between stressful and benign environments.     

Filter feeding,deviations from bilateral symmetry,developmental noise,and heterochrony of hemichordate and cephalochordate gills

We measured gill slit fluctuating asymmetry (FA), a measure of developmental noise, in adults of three invertebrate deuterostomes with different feeding modes: the cephalochordate Branchiostoma floridae (an obligate filter feeder), the enteropneusts Protoglossus graveolens (a facultative filter feeder/deposit feeder) and Saccoglossus bromophenolosus (a deposit feeder). FA was substantially and significantly low in B. floridae and P. graveolens and high in S. bromophenolosus. Our results suggest that the gills of species that have experienced a relaxation of the filter feeding trait exhibit elevated FA. We found that the timing of development of the secondary collagenous gill bars, compared to the primary gill bars, was highly variable in P. graveolens but not the other two species, demonstrating an independence of gill FA from gill bar heterochrony. We also discovered the occasional ectopic expression of a second set of paired gills posterior to the first set of gills in the enteropneusts and that these were more common in S. bromophenolosus. Moreover, our finding that gill slits in enteropneusts exhibit bilateral symmetry suggests that the left‐sidedness of larval cephalochordate gills, and the directional asymmetry of Cambrian stylophoran echinoderm fossil gills, evolved independently from a bilaterally symmetrical ancestor.     

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.     

Courtship and genetic quality: asymmetric males show their best side

Fluctuating asymmetry (FA), the small random deviations from perfect morphological symmetry that result during development, is ubiquitous throughout the animal kingdom. In many species, FA seems to play a role in mate choice, perhaps because it signals an individual''s genetic quality and health. However, the relationship between an individual''s FA and behaviour is generally unknown: what do more asymmetric individuals do about their own asymmetry? We now show for the first time that individuals respond behaviourally to their own morphological FA in what appears to be an adaptive manner. During courtship, male guppies exhibiting high FA in ornamental colour, bias their displays towards their more colourful body side, thus potentially increasing their attractiveness by exaggerating the quantity of their orange signal. This appears to be a strictly behavioural male response to cues provided by females, as it does not occur when males court a non-reactive model female. Whether inferior males realize any mating advantage remains uncertain, but our study clearly demonstrates a behavioural response to random morphological asymmetries that appears to be adaptive. We propose that the tendency to show or otherwise use a ‘best side’ is common in nature, with implications for sexual signalling and the evolution of more pronounced asymmetries.     

Fluctuating asymmetry and age in children: evolutionary implications for the control of developmental stability

Fluctuating asymmetry (FA) is small deviations from perfect symmetry which reflect one component of fitness, i.e. developmental stability. There is accumulating evidence that low FA is important in inter- and intra-sexual selection in humans. However, there is little information on the pattern of FA in children. Data from cross-sectional studies of 680 participants from 2–18 years suggests that (1) both absolute and relative FA reduces with age until 10 years (2) there is an increase in FA in adolescents (11–15 years) with a peak at 13 years for males and 14 years for females (3) after 15 years there is reduction in FA which is maintained until 18 years. The importance of growth rate, metabolic maintenance and sex steroids on developmental stability is discussed.     

FLUCTUATING ASYMMETRY DOES NOT CONSISTENTLY REFLECT SEVERE DEVELOPMENTAL DISORDERS IN HUMAN FETUSES

Developmental instability (DI), as measured by fluctuating asymmetry (FA), may reflect fitness and facilitate the expression of morphological variation. Insights in the underlying mechanisms and magnitude of DI during early development would increase our understanding of its role in evolutionary biology. We studied associations between FA and congenital abnormalities of different origins and functional systems in deceased human fetuses. Major congenital abnormalities corresponded to severe, often-lethal developmental disorders disrupting normal development from early organogenesis onward, but only moderately increased FA. Lower FA with age also supported the hypothesis that more severe abnormalities, leading to an earlier death, increased DI. Although FA related significantly to measures of fitness or health, we anticipated stronger associations because fetal health problems were detrimental. Furthermore, elevated FA occurred in only 4 of 17 disorders (left–right patterning, limb defects, and problems of bronchopulmonary and urogenital system). Fetuses experiencing major abnormalities other than these four types did not show increased FA. This suggests that the functional importance of symmetry in limbs has resulted in strong selection for symmetry and reduced its sensitivity to stress. Finally, the observed patterns suggest that specific developmental pathways have a stronger effect on DI than others do.     

Biotic and Abiotic Factors Affecting Brevicoryne brassicae (L.) (Hemiptera: Aphididae) and the Associated Hyperparasitoid Alloxysta fuscicornis Hartig (Hymenoptera: Figitidae) Morphologies

This study investigates the influence of biotic and abiotic factors associated with the morphological development of Brevicoryne brassicae (Linnaeus) and the associated hyperparasitoid Alloxysta fuscicornis (Hartig). The experiment involved the examination of whether aphid size was influenced by their vertical distribution and density on the host plant, as well as whether variations in hyperparasitoid size and symmetry were correlated with those of their aphid hosts. An aphid multivariate size index was obtained using principal component analysis, while symmetry was evaluated in terms of fluctuating asymmetry (FA). Samples were collected in 2007 on cabbage plants cultivated at an experimental farm located in Uberlandia, Minas Gerais, Brazil (18°56??54???S; 48°12??46???W). The results demonstrated that the size of B. brassicae was negatively associated with temperature, but not with its vertical distribution on the host plant. Temperature was also negatively correlated with hyperparasitoid size. During warmer periods, females produced large quantities of small-sized offspring, whereas an opposite pattern, i.e. the production of fewer offspring of larger size took place during colder periods. This type of adjustment involving trade-offs between physiological and morphological mechanisms, as well as individual interaction with abiotic environmental factors, such as temperature, can be considered an adaptive plastic response in order to increase the chances of survival at a given locality. The encountered relationship between aphid and hyperparasitoid sizes may be an after effect of their indirectly biotic interaction. Hyperparasitoid FA was dependent on the width of the mummified aphids. However, the hypothesis that temperature and vertical distribution on the host plant might influence FA was not confirmed.     

Are human preferences for facial symmetry focused on signals of developmental instability?

Humans find symmetrical faces more attractive than are asymmetricalfaces. Evolutionary psychologists claim that our preferencefor symmetry can be explained in the context of mate choicebecause symmetry is an honest indicator of the genetic qualityof potential mates. These arguments assume that asymmetry inhuman faces is fluctuating asymmetry (FA), because this formof asymmetry can be revealing of developmental instability.However, no study has yet examined the characteristics of facialasymmetry. Here we provide the first detailed study of the patternsof asymmetry in human faces. We measured asymmetry in 35 facialtraits. Although some traits had distributions characteristicof FA, many had distributions that characterize directionalasymmetry (DA); on average, both men and women had right hemi-facedominance. For DA traits we used deviations from the mean asymmetryas a measure of developmental instability. Our measures of asymmetryaccounted for a moderate proportion of the variance in perceivedsymmetry. Importantly, only FAs and random deviations from DAcontributed to people's perception of symmetry. DA was not importantin symmetry judgments. Faces rated as symmetrical were alsorated as attractive. Random deviations from DA were weakly relatedto women's attractiveness judgments of men's faces. DAs didnot influence attractiveness judgments. Our data suggest thatpeople focus on aspects of facial asymmetry that may be revealingof developmental instability. Further studies that isolate FAfrom other forms of asymmetry are required to accurately assessthe influence of developmental instability on the quality ofindividuals and its potential role in mate preferences.     

Fluctuating asymmetry in the otoliths of larval fish as an indicator of condition: conceptual and methodological aspects

Developmental instability, measured as fluctuating asymmetry (FA) in bilateral traits, has been used widely as an indicator of genetic or environmental stress in a variety of plant and animal taxa. FA arises as small deviations from perfect bilateral symmetry which reflect 'mistakes' in developmental processes resulting from the inability of the genotype to buffer itself effectively against environmental perturbations. Recently, it has been proposed that FA in the otoliths can be used as an indicator of condition in larval fish. This paper reviews the conceptual and methodological aspects of FA relevant to its potential use as a measure of well-being. Its simplicity makes FA an attractive tool to measure developmental precision and condition. However, there are several pitfalls, such as measuring error or potentially size dependence. Subtle asymmetries, i.e. between sides variation of a trait at the individual level, may not always be indicative of condition and should be interpreted with caution. The past-growth record of otoliths may provide a powerful means of studying the development of asymmetries at the level of the individual.