Do women's preferences for symmetry change across the menstrual cycle?

In many species, symmetry enhances physical attractiveness of the face and body. In humans, facial attractiveness is also enhanced by symmetrical decoration in the form of facial paint [Cárdenas, R. A., & Harris, L. J. (2006)]. According to the good-genes hypothesis [e.g., Thornhill, R., & Gangestad, S. W. (1999)], symmetry is preferred because it is associated with mate quality. According to the receiver bias hypothesis [e.g., Enquist, M., & Johnstone, R. (1997)], it is a by-product of how the visual system is designed. Proponents of the good-genes hypothesis have suggested that a preference for symmetry may vary with fertility, namely, that it will be enhanced in women in the high-fertility phase of the menstrual cycle. Previous research does demonstrate that, during this phase, women prefer the scent of more symmetrical men [e.g., Gangestad, S. W., & Thornhill, R. (1998)]. However, research employing assessment of faces fails to find a similar effect [Koehler, N., Rhodes, G., & Simmons, L. W. (2002)]. Previous research asked subjects to judge faces one at a time during high fertility (around ovulation) and low fertility (menstruation). We used a different face-presentation method, tested women during the other low-fertility (midluteal) phase, and used decorated as well as undecorated faces. As in our prior study [Cárdenas, R. A., & Harris, L. J. (2006)], symmetry of facial features and symmetry of decoration enhanced attractiveness, but, contrary to the possible prediction of the good-genes hypothesis, the effects did not vary across the cycle. The results as they are, therefore, can be equally accommodated by both hypotheses.     

Facial attractiveness,developmental stability,and fluctuating asymmetry

Despite robust cross-cultural reliability of human facial attractiveness ratings, research on facial attractiveness has only superficially addressed the connection between facial attractiveness and the history of sexual selection in Homo sapiens. There are reasons to believe that developmental stability and phenotypic quality are related. Recent studies of nonhuman animals indicate that developmental stability, measured as fluctuating asymmetry in generally bilateral symmetrical traits, is predictive of performance in sexual selection: Relatively symmetrical males are advantaged under sexual selection. This pattern is suggested by our study of facial attractiveness and fluctuating asymmetry in seven bilateral body traits in a student population. Overall, facial attractiveness negatively correlated with fluctuating asymmetry; the relation for men, but not for women, was statistically reliable. Possible confounding factors were controlled for in the analysis.     

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.     

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.     

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.     

The Body and Face of Woman: One Ornament that Signals Quality?

Evidence has accumulated in recent years supporting the hypothesis that both facial and bodily physical attractiveness in humans are certifications of developmental and hormonal health. Such evidence indicates that physical attractiveness is an honest or Zahavian signal of phenotypic and genetic quality. The hypothesis that physical beauty connotes health was first proposed by Westermarck and was discussed later by Ellis and Symons. It has been suggested that facial attractiveness in women is a deceptive signal of youth, unrelated to phenotypic and genetic quality. This sensory-bias or super-stimulus hypothesis is not supported by this study of men’s ratings of the attractiveness of photographs of 92 nude women. Independent ratings of photographs of faces, fronts with faces covered, and backs of the same women are significantly, positively correlated. The correlation between the ratings of different photos implies that women’s faces and external bodies comprise a single ornament of honest mate value, apparently constructed during puberty by estrogen and also probably by developmental adaptations for symmetry. Thus, women’s physical attractiveness in face and body honestly signal hormonal and perhaps developmental health.     

People with multiple tattoos and/or piercings are not at increased risk for HBV or HCV in The Netherlands

Background

Although published results are inconsistent, it has been suggested that tattooing and piercing are risk factors for HBV and HCV infections. To examine whether tattooing and piercing do indeed increase the risk of infection, we conducted a study among people with multiple tattoos and/or piercings in the Netherlands who acquired their tattoos and piercings in the Netherlands and/or abroad.

Methods

Tattoo artists, piercers, and people with multiple tattoos and/or piercings were recruited at tattoo conventions, shops (N = 182), and a biannual survey at our STI-outpatient clinic (N = 252) in Amsterdam. Participants were interviewed and tested for anti-HBc and anti-HCV. Determinants of HBV and HCV infections were analysed using logistic regression analysis.

Results

The median number of tattoos and piercings was 5 (IQR 2–10) and 2 (IQR 2–4), respectively. Almost 40% acquired their tattoo of piercing abroad. In total, 18/434 (4.2%, 95%CI: 2.64%–6.46%) participants were anti-HBc positive and 1 was anti-HCV positive (0.2%, 95%CI: 0.01%–1.29%). Being anti-HBc positive was independently associated with older age (OR 1.68, 95%CI: 1.03–2.75 per 10 years older) and being born in an HBV-endemic country (OR 7.39, 95%CI: 2.77–19.7). Tattoo- and/or piercing-related variables, like having a tattoo or piercing in an HBV endemic country, surface percentage tattooed, number of tattoos and piercings etc., were not associated with either HBV or HCV.

Conclusions

We found no evidence for an increased HBV/HCV seroprevalence among persons with multiple tattoos and/or piercings, which might be due to the introduction of hygiene guidelines for tattoo and piercing shops in combination with the low observed prevalence of HBV/HCV in the general population. Tattoos and/or piercings, therefore, should not be considered risk factors for HBV/HCV in the Dutch population. These findings imply the importance of implementation of hygiene guidelines in other countries.     

Carcass Decoration Changes Web Structure and Prey Capture Rate in an Orb-Web Spider, Cyclosa mulmeinensis (Araneae, Araneidae)

Cyclosa spiders attach prey carcasses as decorations to their webs, but the functions of the carcasses are unclear and controversial. We investigated distinctive features of these webs in the field and conducted prey-capture experiments in the lab using the orb-web spider Cyclosa mulmeinensis. Webs with attached decoration had a significantly narrower mesh width than those without decoration and a higher degree of vertical asymmetry in the web’s shape. In the laboratory, webs without decorations trapped significantly more prey, even though other features of the webs were nearly identical. These results suggest that web decorations do not attract prey in this species, but might play other roles such as blinding predators to the spider’s presence.     

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 sound of symmetry: Voice as a marker of developmental instability

Low fluctuating asymmetry (FA, a measure of deviation from bilateral symmetry) appears to be a phenotypic marker of reproductive viability and health. In the present study, we investigated whether ratings of voice attractiveness were correlated with variations in FA. Several bilateral traits were measured to calculate a FA index and independent raters who did not know and never saw the subjects assessed the attractiveness of recordings of each subject's voice. Voices of subjects with greater bilateral symmetry were rated as more attractive by members of both sexes than those with asymmetrical traits.     

Facial symmetry and judgements of apparent health: Support for a “good genes” explanation of the attractiveness–symmetry relationship

The “good genes” explanation of attractiveness posits that mate preferences favour healthy individuals due to direct and indirect benefits associated with the selection of a healthy mate. Consequently, attractiveness judgements are likely to reflect judgements of apparent health. One physical characteristic that may inform health judgements is fluctuating asymmetry as it may act as a visual marker for genetic quality and developmental stability. Consistent with these suggestions, a number of studies have found relationships between facial symmetry and facial attractiveness. In Study 1, the interplay between facial symmetry, attractiveness, and judgements of apparent health was explored within a partial correlation design. Findings suggest that the attractiveness–symmetry relationship is mediated by a link between judgements of apparent health and facial symmetry. In Study 2, an opposite-sex bias in sensitivity to facial symmetry was observed when judging health. Thus, perceptual analysis of symmetry may be an adaptation facilitating discrimination between potential mates on the basis of apparent health. The findings of both studies are consistent with a “good genes” explanation of the attractiveness–symmetry relationship and problematic for the claim that symmetry is attractive as a by-product of the ease with which the visual recognition system processes symmetric stimuli.     

Are large wattles related to particular MHC genotypes in the male pheasant?

In sexually dimorphic species, partners can assess heritable mate quality by analyzing costly sexual ornaments in terms of their dimension and possibly of their symmetry. In vertebrates an important aspect of genetic quality is the efficiency of the immune system, and in particular the Major Histocompatibility Complex (MHC). If ornaments are honest advertisements of pathogen resistance (good genes), in line with the Hamilton-Zuk hypothesis, a correlation between ornament expression and MHC profiles should exist. We tested this hypothesis in the common pheasant Phasianus colchicus by comparing male ornament characteristics (wattle and spur size, and wattle fluctuating asymmetry) with a portion of exon 2 of the class IIB MHC genes containing 19 putative antigen recognition sites. A total of 8 new alleles was observed in the MHCPhco exon IIB. We found significant differences in the occurrence of MHC genotypes between males carrying large or small wattles. Homozygous genotypes predicted large wattle males more correctly than small wattle males. The association between the dimension of the spur and the occurrence of MHC genotypes was marginally significant, however, we did not find any significant association between MHC genotypes and asymmetry. Our results suggest that female pheasants may use the ornament size as a cue to evaluate male quality and thus choose males carrying particular MHC profiles.     

Energetic stress and the degree of fluctuating asymmetry: Implications for a long-lasting,honest signal

Summary Duplicate, bilateral structures of individual animals are usually symmetrical. In cases where such structures are asymmetrical, the degree of asymmetry may indicate the propensity of an individual to stray from the genetically programmed outcome during the development of the structure. Asymmetries have recently been assumed to constitute an honest signal of male quality and, as such, a cue for female choice. I tested the assumption that different rates of energy intake would produce differences in the degree of asymmetry by measuring original and induced fourth rectrices of both sides of the body in European nuthatchesSitta europaea. I found no predominance for the right or left side, thus showing the fluctuating nature of the asymmetry at a population level. This was not the case within individuals which consistently had a longer fourth rectrix on one or the other side of the body. Induced rectrices, grown during winter when food availability was relatively low, exhibited a higher degree of asymmetry than did such rectrices grown during winter after hoardable food had been provided earlier during the winter. The original rectrices, grown during relatively benign conditions in late summer, showed the smallest degree of fluctuating asymmetry. This indicates that the degree of asymmetry is affected by the rate of energy intake. Thus, male quality, reflecting the rate with which energy can be secured and shown by differing degrees of asymmetry, can be used as an honest, long-lasting cue by females in their choice of a mate.     

The Scent of Symmetry: A Human Sex Pheromone that Signals Fitness?

A previous study by the authors showed that the body scent of men who have greater body bilateral symmetry is rated as more attractive by normally ovulating (non-pill-using) women during the period of highest fertility based on day within the menstrual cycle. Women in low-fertility phases of the cycle and women using hormone-based contraceptives do not show this pattern. The current study replicated these findings with a larger sample and statistically controlled for men's hygiene and other factors that were not controlled in the first study. The current study also examined women's scent attractiveness to men and found no evidence that men prefer the scent of symmetric women. We propose that the scent of symmetry is an honest signal of phenotypic and genetic quality in the human male, and chemical candidates are discussed. In both sexes, facial attractiveness (as judged from photos) appears to predict body scent attractiveness to the opposite sex. Women's preference for the scent associated with men's facial attractiveness is greatest when their fertility is highest across the menstrual cycle. The results overall suggest that women have an evolved preference for sires with good genes.     

Stealing behavior and the maintenance of a visual display in the satin bowerbird

Honest signals that indicate male quality have been observedin many species and are thought to have evolved to allow malesto assess rivals accurately and respond to "cheaters." Femalescould potentially also use the same honest signals as reliableindicators of male quality. In bowerbirds, the numbers of specificbower decorations may serve as an honest signal of male quality:this study investigates whether decoration stealing among malesatin bowerbirds at the Bunya Mountains, Australia, may alsoinvolve honest signals. In this study, we aimed to determine1) predictors for the degree to which individual male satinbowerbirds steal, and are stolen from, and 2) predictors forwhy some male pairs interact by stealing, whereas other pairsdo not. We also assessed how experimentally standardizing thenumber of decorations on bowers would affect the 1) frequencyof stealing, 2) specific interactions among males, and 3) distributionof decorations across bowers. Bower decorations were labeledand tracked through one breeding season. Males that were successfulstealers, stole from other successful stealers, had many feathersand bottle tops on their bowers and painted their bower wallsoften. Male pairs were more likely to interact by stealing iftheir bowers were in close proximity. Most of the stealing observedwas of a reciprocal nature. After we standardized the numbersand types of decorations on a small group of males' bowers,the mean number of daily stealing gains and the total numberof males interacting by stealing did not change. In addition,no significant novel stealing interactions were initiated afterthe manipulation. The average number of all bower decorationsand the average number of rosella feathers on a given male'sbower prior to the manipulation were proportional to the averagenumbers for the period after the manipulation. Furthermore,males that originally had better collections of decorationstended to suffer fewer losses due to stealing after the manipulation.Our results suggest that the total number of decorations, thetotal number of rosella feathers on a male's bower, and possiblystealing behavior, may form part of the basis of an honest signalindicating male quality and therefore might be correlated withmating success.     

Fluctuating asymmetry in red junglefowl

Fluctuating asymmetry, the random deviation from perfect bilateral symmetry, has recently attracted considerable attention. Levels of asymmetry have been shown to correlate with measures of individual quality. We measured asymmetry in a variety of ornamental and non-ornamental traits in red junglefowl, Gallus gallus and examined the patterns of asymmetry among different traits within an individual. All ornamental traits had significantly higher levels of fluctuating asymmetry than did non-ornamental traits. However, inter-trait correlations of asymmetry were low for both ornamental and non-ornamental traits. We then correlated measures of asymmetry with several potential indicators of male quality, including comb size, body size, and body condition. We found little evidence that asymmetry in any measured trait reflected male quality. We measured asymmetry in ornamental traits at several stages of development and found no relationship between male condition and changes in asymmetry over time. Our results indicate that it is necessary to employ caution when choosing traits to be measured in studies of fluctuating asymmetry and that a relationship between asymmetry and individual quality cannot be assumed.     

Facial attractiveness,symmetry, and physical fitness in young women

This study explores the evolutionary-based hypothesis that facial attractiveness (a guiding force in mate selection) is a cue for physical fitness (presumably an important contributor to mate value in ancestral times). Since fluctuating asymmetry, a measure of developmental stability, is known to be a valid cue for fitness in several biological domains, we scrutinized facial asymmetry as a potential mediator between attractiveness and fitness. In our sample of young women, facial beauty indeed indicated physical fitness. The relationships that pertained to asymmetry were in the expected direction. However, a closer analysis revealed that facial asymmetry did not mediate the relationship between fitness and attractiveness. Unexpected problems regarding the measurement of facial asymmetry are discussed.     

Human body odour, symmetry and attractiveness.

Several studies have found body and facial symmetry as well as attractiveness to be human mate choice criteria. These characteristics are presumed to signal developmental stability. Human body odour has been shown to influence female mate choice depending on the immune system, but the question of whether smell could signal general mate quality, as do other cues, was not addressed in previous studies. We compared ratings of body odour, attractiveness, and measurements of facial and body asymmetry of 16 male and 19 female subjects. Subjects wore a T-shirt for three consecutive nights under controlled conditions. Opposite-sex raters judged the odour of the T-shirts and another group evaluated portraits of the subjects for attractiveness. We measured seven bilateral traits of the subject's body to assess body asymmetry. Facial asymmetry was examined by distance measurements of portrait photographs. The results showed a significant positive correlation between facial attractiveness and sexiness of body odour for female subjects. We found positive relationships between body odour and attractiveness and negative ones between smell and body asymmetry for males only if female odour raters were in the most fertile phase of their menstrual cycle. The outcomes are discussed in the light of different male and female reproductive strategies.     

Symmetry and Human Facial Attractiveness

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.     

Ecological stress memory: Evidence in two out of seven species through the examination of the relationship between leaf fluctuating asymmetry and photosynthesis

Increased morphological fluctuating asymmetry is considered as an indication that the extent of a natural stress has surpassed the ability of the genotype to maintain the normal symmetry in the body plan. Young leaves can suffer by a variety of stresses, such as nutrient deficiencies, drought, heat and cold in combination with high light. Therefore, increased morphological fluctuating asymmetry in mature leaves may be considered as an ecological indicator of such environmental pressures. Hence, deviations from symmetry in a mature leaf may be a reminder of an adversity having occurred when the leaf was young and developing. We argued that a past stress may stigmatize future photosynthesis and we searched for correlations between leaf fluctuating asymmetry and photosynthetic parameters obtained from fast chlorophyll a fluorescence rise curves in mature leaves from seven tree species. The results were species-specific, with four species (Arbutus unedo, Cercis siliquastrum, Platanus orientalis and Populus alba) showing both maximum quantum yield of photosystem II and photosynthetic performance index (PI_total sensu Strasser) to be independent of the alleged juvenile stress, while in one species (Ceratonia siliqua) the two parameters were negatively correlated to leaf fluctuating asymmetry. Interestingly, in two species (Olea europaea and Pistacia lentiscus), higher leaf asymmetry was linked with lower risk of chronic photoinhibitory damage and higher photosynthetic capacity. An ‘ecological stress memory’ may be inferred for some species improving their tolerance to future adversities and global change.