Sexually dimorphic traits are associated with subsistence strategy in African faces from the Sahel/Savannah belt

OBJECTIVES

Previous research revealed that in some African populations, food-production strategies are associated with facial shape. Nomadic pastoralists living in the African Sahel/Savannah belt have a different facial morphology than their sedentary neighbors. We investigated whether the lifestyle associated with a subsistence pattern has an impact on sexual dimorphism in the facial structure.

METHODS

We employed several methods from geometric morphometrics and demonstrated such effect in four ethnically distinct populations that share the same geographic space.

RESULTS

We show that the facial traits which correlate with a subsistence strategy are systematically associated with levels of facial sex-typicality. In particular, we found that faces with more pronounced pastoralist features have on average more masculine facial traits and that this effect is more pronounced in men than in women.

CONCLUSIONS

In general, though, the magnitude of overall facial dimorphism does not differ between pastoralists and farmers. Pastoralists (in contrast to farmers) tend to have a more masculine facial morphology but facial differences between the sexes are in both groups the same.

Congruence in European and Asian perception of Vietnamese facial attractiveness, averageness, symmetry and sexual dimorphism

Attractiveness is a proposed universal cue to overall biological quality. Nonetheless, local raters and raters of the same ethnicity may be more accurate in assessing the cues for attractiveness than distant and unfamiliar raters. Shared ethnicity and shared environment may both affect rating accuracy: our aim was to compare their relative influence. Therefore, we photographed young Vietnamese participants (N = 93, 33 women) from Hanoi, Vietnam. The photographs were rated by Czechs, Asian Vietnamese, and Czech Vietnamese (raters of Vietnamese origin who lived in Czechia for all or most of their life). Using geometric morphometrics, we measured facial shape cues to biological quality: averageness, asymmetry, and sexual dimorphism. We expected that Vietnamese raters residing in Czechia and Vietnam would agree on perceived attractiveness and use shape-related facial cues to biological quality better than Czech European raters, who are less familiar with East Asians. Surprisingly, mixed-effect models and post hoc comparisons identified no major cross-group differences in attributed attractiveness and path analyses revealed that the three groups based their rating on shape-related characteristics in a similar way. However, despite the considerable cross-cultural agreement regarding perceived attractiveness, Czech European raters associated attractiveness with facial shape averageness significantly more than Vietnamese raters.

Attractiveness Differentially Affects Direct Versus Indirect Face Evaluations in Two Cultures

Although decades of research have identified facial features relating to people's evaluations of faces, specific features have largely been examined in isolation from each other. Recent work shows that considering the relative importance of these features in face evaluations is important to test theoretical assumptions of impression formation. Here, we examined how two facial features of evolutionary interest, facial attractiveness and facial-width-to-height ratio (FWHR), relate to evaluations of faces across two cultures. Because face evaluations are typically directly measured via self-reports, we also examined whether these features exert differential effects on both direct and indirect face evaluations. Evaluations of standardized photos naturally varying in facial attractiveness and FWHR were collected using the Affect Misattribution Procedure in the United States and Turkey. When their relative contributions were considered in the same model, facial attractiveness, but not FWHR, related to face evaluations across cultures. This positive attractiveness effect was stronger for direct versus indirect evaluations across cultures. These findings highlight the importance of considering the relative contributions of facial features to evaluations across cultures and suggest a culturally invariant role of attractiveness when intentionally evaluating faces.

Is there no beauty in sexually dimorphic eyes? Facial attractiveness and White Europeans ocular morphology-Brief communication

The link between human ocular morphology and attractiveness, especially in the context of its potential adaptive function, is an underexplored area of research. In our study, we examined the association between facial attractiveness and three sexually dimorphic measures of ocular morphology in White Europeans: the sclera size index, width-to-height ratio, and relative iris luminance. Sixty participants (30 women) assessed the attractiveness of the opposite-sex photographs of 50 men and 50 women. Our results show that in both men and women, none of the three measures was linked to the opposite sex ratings of facial attractiveness. We conclude that those ocular morphology measures may play a limited role in human mate preferences.

Visible beyond Violet: How Butterflies Manage Ultraviolet

Ultraviolet (UV) means ‘beyond violet’ (from Latin ‘ultra’, meaning ‘beyond’), whereby violet is the colour with the highest frequencies in the ‘visible’ light spectrum. By ‘visible’ we mean human vision, but, in comparison to many other organisms, human visual perception is rather limited in terms of the wavelengths it can perceive. Still, this is why communication in the UV spectrum is often called hidden, although it most likely plays an important role in communicating various kinds of information among a wide variety of organisms. Since Silberglied’s revolutionary Communication in the Ultraviolet, comprehensive studies on UV signals in a wide list of genera are lacking. This review investigates the significance of UV reflectance (and UV absorption)—a feature often neglected in intra- and interspecific communication studies—mainly in Lepidoptera. Although the text focuses on various butterfly families, links and connections to other animal groups, such as birds, are also discussed in the context of ecology and the evolution of species. The basic mechanisms of UV colouration and factors shaping the characteristics of UV patterns are also discussed in a broad context of lepidopteran communication.

Symptomic Mimicry Between SARS-CoV-2 and the Common Cold Complex

The recent changes in COVID-19 symptoms suggest convergent evolution of respiratory diseases. This process is analogous to the emergence of animal mimetic complexes and complements previously identified types of mimicry. A novel pathogen might go unnoticed or insufficiently counteracted if it resembles a disease that the host already faced on multiple occasions, which creates a selective pressure towards a typical symptomic phonotype. In short, the reason why so many unrelated pathogens cause similar symptoms may correspond to the reasons that drove the evolution of the 'warning' wasp-like colouration in various insect species.

Predicting strength from aggressive vocalizations versus speech in African bushland and urban communities

The human voice carries information about a vocalizer's physical strength that listeners can perceive and that may influence mate choice and intrasexual competition. Yet, reliable acoustic correlates of strength in human speech remain unclear. Compared to speech, aggressive nonverbal vocalizations (roars) may function to maximize perceived strength, suggesting that their acoustic structure has been selected to communicate formidability, similar to the vocal threat displays of other animals. Here, we test this prediction in two non-WEIRD African samples: an urban community of Cameroonians and rural nomadic Hadza hunter-gatherers in the Tanzanian bushlands. Participants produced standardized speech and volitional roars and provided handgrip strength measures. Using acoustic analysis and information-theoretic multi-model inference and averaging techniques, we show that strength can be measured from both speech and roars, and as predicted, strength is more reliably gauged from roars than vowels, words or greetings. The acoustic structure of roars explains 40-70% of the variance in actual strength within adults of either sex. However, strength is predicted by multiple acoustic parameters whose combinations vary by sex, sample and vocal type. Thus, while roars may maximally signal strength, more research is needed to uncover consistent and likely interacting acoustic correlates of strength in the human voice. This article is part of the theme issue 'Voice modulation: from origin and mechanism to social impact (Part I)'.

Sexual Dimorphism in Facial Contrast: A Case from Central Africa

Apart from morphological differences, male and female faces also vary in color, especially in overall lightness and facial contrast, i.e., the contrast between the luminance and color of facial features (eyes, lips, or brows) and luminance and color of the surrounding skin. In many populations, it has been demonstrated that women tend to be lighter than men. Other differences were found in facial contrast: women have a higher contrast between the lightness of their eyes and lips and the surrounding skin. Manipulation of this contrast in an artificial genderless face can result in a masculine or feminine appearance. So far, however, this phenomenon has been studied mostly in Euro-American and East Asian samples, with little evidence from populations with darker facial tone. We explored natural sexual dimorphism in both facial contrast and lightness in an African, namely Cameroonian, sample, and compared it with results for a European, in particular Czech, population. Our findings showed that sexual differences in luminance contrast of eyes and brows were in both studied populations similar but in the Cameroonian sample, significant difference in lips contrast was absent. These results indicate that sex differences in facial contrast are a side effect of the sex differences in skin color and can be used as a proxy for skin color perception.

Differential effects of resource scarcity and pathogen prevalence on heterosexual women's facial masculinity preferences

The present research focused on how environmental harshness may affect heterosexual women's preferences of potential male mates' facial characteristics, namely masculinity-femininity. The evidence on this issue is mixed and mostly from Western samples. We aimed to provide causal evidence using a sample of Turkish women and Turkish male faces. A video-based manipulation was developed to heighten environmental harshness perceptions. In the main experiment, participants were primed with resource scarcity, pathogen prevalence or neither (control). They then saw masculinised vs. feminised versions of the same faces and indicated the face that they would prefer for a long-term relationship and separately rated the faces on various dimensions. In general, masculinised faces were perceived as slightly more attractive, slightly healthier and much more formidable. A multilevel Bayesian model showed that pathogen prevalence lowered the preference for masculinised faces while resource scarcity weakly elevated it. The overall drop in attractiveness ratings in cases of high perceived pathogen prevalence, one of the strongest effects we observed, suggests that during epidemics, the formation of new relationships is not a favourable strategy. Implications for evolutionary theories of mate preference are discussed.

Facial attractiveness and preference of sexual dimorphism: A comparison across five populations

Despite intensive research, evolutionary psychology has not yet reached a consensus regarding the association between sexual dimorphism and attractiveness. This study examines associations between perceived and morphological facial sexual dimorphism and perceived attractiveness in samples from five distant countries (Cameroon, Colombia, Czechia, Iran and Turkey). We also examined possible moderating effects of skin lightness, averageness, age, body mass and facial width. Our results suggest that in all samples, women's perceived femininity was positively related to their perceived attractiveness. Women found perceived masculinity in men attractive only in Czechia and Colombia, two distant populations. The association between perceived sexual dimorphism and attractiveness is thus potentially universal only for women. Across populations, morphological sexual dimorphism and averageness are not universally associated with either perceived facial sexual dimorphism or attractiveness. With our exploratory approach, results highlight the need for control of which measure of sexual dimorphism is used (perceived or measured) because they affect perceived attractiveness differently. Morphological averageness and sexual dimorphism are not good predictors of perceived attractiveness. It is noted that future studies should use samples from multiple populations to allow for identification of specific effects of local environmental and socioeconomic conditions on preferred traits in unmanipulated local facial stimuli.

Perception-driven dynamics of mimicry based on attractor field model

We provide a formal account of an interface that bridges two different levels of dynamic processes manifested by mimicry: prey-prey interactions and predators' perception. Mimicry is a coevolutionary process between an animate selective agent and at least two similar organisms selected by agent's perception-driven actions. Attractor field model explains perceived similarity of forms by noting that in both human and animal cognition, morphologically intermediate forms are more likely to be perceived as belonging to rare rather than abundant forms. We formalize this model in terms of predators' perception space deformation using numerical simulations and argue that the probability of confusion between similar species creates pressure on the perception space, which in turn leads to inflation of regions of perception space with high density of species representations. Such inflation causes increased discrimination between species by a predator, which implies that adaptive mimicry could initially emerge more easily among atypical species because they do not need the same level of similarity to the model. We provide a theoretical instrument to conceptualize interdependence between objective measurable matrices and perceived matrices of the same external reality. We believe that our framework leads to a more precise understanding of the evolution of mimicry.

Environmental convergence in facial preferences: a cross-group comparison of Asian Vietnamese, Czech Vietnamese, and Czechs

It has been demonstrated that sociocultural environment has a significant impact on human behavior. This contribution focuses on differences in the perception of attractiveness of European (Czech) faces as rated by Czechs of European origin, Vietnamese persons living in the Czech Republic and Vietnamese who permanently reside in Vietnam. We investigated whether attractiveness judgments and preferences for facial sex-typicality and averageness in Vietnamese who grew up and live in the Czech Republic are closer to the judgements and preferences of Czech Europeans or to those of Vietnamese born and residing in Vietnam. We examined the relative contribution of sexual shape dimorphism and averageness to the perception of facial attractiveness across all three groups of raters. Czech Europeans, Czech Vietnamese, and Asian Vietnamese raters of both sexes rated facial portraits of 100 Czech European participants (50 women and 50 men, standardized, non-manipulated) for attractiveness. Taking Czech European ratings as a standard for Czech facial attractiveness, we showed that Czech Vietnamese assessments of attractiveness were closer to this standard than assessments by the Asian Vietnamese. Among all groups of raters, facial averageness positively correlated with perceived attractiveness, which is consistent with the "average is attractive" hypothesis. A marginal impact of sexual shape dimorphism on attractiveness rating was found only in Czech European male raters: neither Czech Vietnamese nor Asian Vietnamese raters of either sex utilized traits associated with sexual shape dimorphism as a cue of attractiveness. We thus conclude that Vietnamese people permanently living in the Czech Republic converge with Czechs of Czech origin in perceptions of facial attractiveness and that this population adopted some but not all Czech standards of beauty.

A cross-cultural study of sex-typicality and averageness: Correlation between frontal and lateral measures of human faces

OBJECTIVES

Facial averageness and sexual dimorphism are extensively studied attractiveness markers, which are viewed as possible indicators of biological quality. Both are complex morphological traits, and both can be easily assessed from frontal and lateral projection of a human face. Interestingly, examination of mutual relations between the frontal and lateral dimensions of these markers has so far received little attention in published research.

METHODS

In our cross-cultural study, we used geometric morphometric data from male and female faces from Brazil, Cameroon, Colombia, and the Czech Republic, and analyzed correlations between frontal and lateral measurements of averageness and degree of maleness/femaleness, that is, the individual variation in features that characterize sexual dimorphism. We also analyzed whether the association between frontal and lateral measurements differed in men and women.

RESULTS

In general, our results showed a moderate correlation in sexually dimorphic features between lateral and frontal facial configuration in both sexes, while frontal and lateral facial averageness was moderately correlated only in women. This pattern was less consistent when individual populations were analyzed separately.

CONCLUSIONS

We suggest that, in general, the weak association between lateral and frontal facial configurations may be the result of selection pressures in favor of individual identity signals. Moreover, especially in women, the frontal and lateral dimension of a given facial attractiveness marker may provide similar information about the qualities of the individual. The absence of a significant correlation in male facial averageness suggests that frontal and lateral averageness convey different information about an individual.

Body coloration and mechanisms of colour production in Archelosauria: the case of deirocheline turtles

Animal body coloration is a complex trait resulting from the interplay of multiple mechanisms. While many studies address the functions of animal coloration, the mechanisms of colour production still remain unknown in most taxa. Here we compare reflectance spectra, cellular, ultra- and nano-structure of colour-producing elements, and pigment types in two freshwater turtles with contrasting courtship behaviour, Trachemys scripta and Pseudemys concinna. The two species differ in the distribution of pigment cell-types and in pigment diversity. We found xanthophores, melanocytes, abundant iridophores and dermal collagen fibres in stripes of both species. The yellow chin and forelimb stripes of both P. concinna and T. scripta contain xanthophores and iridophores, but the post-orbital regions of the two species differ in cell-type distribution. The yellow post-orbital region of P. concinna contains both xanthophores and iridophores, while T. scripta has only xanthophores in the yellow-red postorbital/zygomatic regions. Moreover, in both species, the xanthophores colouring the yellow-red skin contain carotenoids, pterins and riboflavin, but T. scripta has a higher diversity of pigments than P. concinna. Trachemys s. elegans is sexually dichromatic. Differences in the distribution of pigment cell types across body regions in the two species may be related to visual signalling but do not match predictions based on courtship position. Our results demonstrate that archelosaurs share some colour production mechanisms with amphibians and lepidosaurs (i.e. vertical layering/stacking of different pigment cell types and interplay of carotenoids and pterins), but also employ novel mechanisms (i.e. nano-organization of dermal collagen) shared with mammals.

Positive association between facial and vocal femininity/masculinity in women but not in men

Multicomponent stimuli improve information reception. In women, perceived facial and vocal femininity-masculinity (FM) are concordant; however, mixed results are found for men. Some feminine and masculine traits are related to sex hormone action and can indicate reproductive qualities. However, most of the current research about human mate choice focuses on isolated indicators, especially visual assessment of faces. We therefore examined the cross-modal concordance hypothesis by testing correlations between perceptions of FM based on facial, vocal, and behavioral stimuli. Standardized facial pictures, vocal recordings and dance videos of 38 men and 41 women, aged 18-35 years, were rated by 21 male and 43 female students, aged 18-35 years, on 100-point scale (0 = very feminine; 100 = very masculine). All participants were Brazilian students from University of Sao Paulo. In women, facial and vocal FM correlated positively, suggesting concordant information about mate quality. Such results were not found in men, indicating multiple messages, which agree with women's multifaceted preference for male FM. In both sexes, FM of dance did not correlate with voices or faces, indicating different information and distinct process of development. We thus partially supported the cross-modal concordance hypothesis.

She Always Steps in the Same River: Similarity Among Long-Term Partners in Their Demographic, Physical, and Personality Characteristics

In mate choice, individuals consider a wide pool of potential partners. It has been found that people have certain preferences, but intraindividual stability of mate choice over time remains little explored. We tested individual consistency of mate choice with respect to a number of demographic, physical, and personality characteristics. Only mothers were recruited for this study, because we wanted to find out not only whether women choose long-term partners with certain characteristics but also whether the father of their child(ren) differs from their other long-term (ex-)partners. Women (N = 537) of 19–45 years of age indicated the demographic, physical (by using image stimuli), and personality characteristics of all of their long-term partners (partners per respondent: mean = 2.98, SD = 1.32). Then we compared the average difference between an individual’s long-term partners with the expected average difference using a permutation test. We also evaluated differences between partners who had children with the participants (fathers) and other long-term partners (non-fathers) using permutation tests and mixed-effect models. Our results revealed that women choose long-term partners consistently with respect to all types of characteristics. Although effect sizes for the individual characteristics were rather weak, maximal cumulative effect size for all characteristics together was high, which suggests that relatively low effect sizes were caused by high variability with low correlations between characteristics, and not by inconsistent mate choice. Furthermore, we found that despite some differences between partners, fathers of participants’ child(ren) do fit their ‘type’. These results suggest that mate choice may be guided by relatively stable but to some degree flexible preferences, which makes mate choice cognitively less demanding and less time-consuming. Further longitudinal studies are needed to confirm this conclusion.

Toward a New Approach to Cross-Cultural Distinctiveness and Typicality of Human Faces: The Cross-Group Typicality/ Distinctiveness Metric

In the present research, we took advantage of geometric morphometrics to propose a data-driven method for estimating the individual degree of facial typicality/distinctiveness for cross-cultural (and other cross-group) comparisons. Looking like a stranger in one’s home culture may be somewhat stressful. The same facial appearance, however, might become advantageous within an outgroup population. To address this fit between facial appearance and cultural setting, we propose a simple measure of distinctiveness/typicality based on position of an individual along the axis connecting the facial averages of two populations under comparison. The more distant a face is from its ingroup population mean toward the outgroup mean the more distinct it is (vis-à-vis the ingroup) and the more it resembles the outgroup standards. We compared this new measure with an alternative measure based on distance from outgroup mean. The new measure showed stronger association with rated facial distinctiveness than distance from outgroup mean. Subsequently, we manipulated facial stimuli to reflect different levels of ingroup-outgroup distinctiveness and tested them in one of the target cultures. Perceivers were able to successfully distinguish outgroup from ingroup faces in a two-alternative forced-choice task. There was also some evidence that this task was harder when the two faces were closer along the axis connecting the facial averages from the two cultures. Future directions and potential applications of our proposed approach are discussed.

Predictors of Fighting Ability Inferences Based on Faces

Facial perception plays a key role in various social interactions, including formidability assessments. People make relatively accurate inferences about men's physical strength, aggressiveness, and success in physical confrontations based on facial cues. The physical factors related to the perception of fighting ability and their relative contribution have not been investigated yet, since most existing studies employed only a limited number of threat potential measures or proxies. In the present study, we collected data from Czech Mixed Martial Arts (MMA) fighters regarding their fighting success and physical performance in order to test physical predictors of perceived fighting ability made on the basis of high-fidelity facial photographs. We have also explored the relationship between perceived and actual fighting ability. We created standardized 360° photographs of 44 MMA fighters which were assessed on their perceived fighting ability by 94 raters (46 males). Further, we obtained data regarding their physical characteristics (e.g., age, height, body composition) and performance (MMA score, isometric strength, anaerobic performance, lung capacity). In contrast to previous studies, we did not find any significant links between the actual and the perceived fighting ability. The results of a multiple regression analysis have, however, shown that heavier fighters and those with higher anaerobic performance were judged as more successful. Our results suggest that certain physical performance-related characteristics are mirrored in individuals' faces but assessments of fighting success based on facial cues are not congruent with actual fighting performance.

360 Degrees of Facial Perception: Congruence in Perception of Frontal Portrait, Profile, and Rotation Photographs

Studies in social perception traditionally use as stimuli frontal portrait photographs. It turns out, however, that 2D frontal depiction may not fully capture the entire morphological diversity of facial features. Recently, 3D images started to become increasingly popular, but whether their perception differs from the perception of 2D has not been systematically studied as yet. Here we investigated congruence in the perception of portrait, left profile, and 360° rotation photographs. The photographs were obtained from 45 male athletes under standardized conditions. In two separate studies, each set of images was rated for formidability (portraits by 62, profiles by 60, and 360° rotations by 94 raters) and attractiveness (portraits by 195, profiles by 176, and 360° rotations by 150 raters) on a 7-point scale. The ratings of the stimuli types were highly intercorrelated (for formidability all rs > 0.8, for attractiveness all rs > 0.7). Moreover, we found no differences in the mean ratings between the three types of stimuli, neither in formidability, nor in attractiveness. Overall, our results clearly suggest that different facial views convey highly overlapping information about structural facial elements of an individual. They lead to congruent assessments of formidability and attractiveness, and a single angle view seems sufficient for face perception research.

Distribution of Ultraviolet Ornaments in Colias Butterflies (Lepidoptera: Pieridae)

Ultraviolet patterns in butterflies have been recognized and studied for many years. They are frequently involved in both intraspecific and interspecific interactions. Only a handful of studies, however, have investigated possible links between ultraviolet (UV) reflectance and ecological properties in some genera of the Lepidoptera as a whole. This study examines the impact of habitat and distribution on UV reflectance patterns on the wings of 106 species and subspecies of Colias butterflies. Based on standardized digital photographs, we performed a multivariate analysis of relations between UV reflectance, preferred habitat (alpine, arctic, dry grasslands, humid, forest, and ubiquitous), and distribution area (Afrotropical, Nearctic, Neotropical, European, Caucaso-Anatolian, boreal Eurasian, Central Asian mountains, northern China and Japan, and northern Oriental region). UV patterns occur more frequently in the male (60 taxa) than in female (25 taxa) Coliads. This difference in presence of UV patterns is used for differentiating between the males and females of a given species or subspecies. Further possible explanations of this phenomenon are also discussed. This study also shows that particular configurations of UV patterns are significantly associated with particular distribution areas. This relation is relatively strong but overall trends remain unclear. Based on the results of this study, it can be concluded that there exists a significant difference in the configuration of UV reflectance between the sexes, and that the configuration of UV reflectance significantly interacts with the geographical distribution of Colias species and subspecies.

UV reflectance is associated with environmental conditions in Palaearctic Pieris napi (Lepidoptera: Pieridae)

The subject of our investigation was the visual features of wing color with special focus on the UV reflectance in the green-veined white butterfly (Pieris napi). Previous studies had concluded that UV reflectance on dorsal wing surfaces is found only in the female P. napi. Based on UV sensitive photography, we analyzed a correlation between 12 geographic and environmental factors and UV reflectance patterns on 3 patches on the forewings of 407 P. napi specimens from the Palaearctic region. Results had shown that females significantly differ from males: they exhibit a 25% higher UV reflectance. To investigate whether and how UV reflectance levels on the forewings and hindwings of both sexes are influenced by the environment, we performed a principal component analysis (PCA) with several environmental variables. For several variables (in particular, latitude and longitude, mean annual temperature and precipitation, and temperature annual range and altitude), the generalized linear model (GLM) model revealed a significant correlation in both sexes. This suggests a link between UV reflectance levels and the environment and distribution of P. napi. We found that stronger UV reflectance is associated with generally more hostile environments and concluded that large-scale environmental factors influence the UV reflectance on the forewings of both male and female green-veined white butterflies.

The Bogazici face database: Standardized photographs of Turkish faces with supporting materials

Many sets of human facial photographs produced in Western cultures are available for scientific research. We report here on the development of a face database of Turkish undergraduate student targets. High-resolution standardized photographs were taken and supported by the following materials: (a) basic demographic and appearance-related information, (b) two types of landmark configurations (for Webmorph and geometric morphometrics (GM)), (c) facial width-to-height ratio (fWHR) measurement, (d) information on photography parameters, (e) perceptual norms provided by raters. We also provide various analyses and visualizations of facial variation based on rating norms using GM. Finally, we found that there is sexual dimorphism in fWHR in our sample but that this is accounted for by body mass index. We present the pattern of associations between rating norms, GM and fWHR measurements. The database and supporting materials are freely available for scientific research purposes.

Health status by gender, hair color, and eye color: Red-haired women are the most divergent

Red hair is associated in women with pain sensitivity. This medical condition, and perhaps others, seems facilitated by the combination of being red-haired and female. We tested this hypothesis by questioning a large sample of Czech and Slovak respondents about the natural redness and darkness of their hair, their natural eye color, their physical and mental health (24 categories), and other personal attributes (height, weight, number of children, lifelong number of sexual partners, frequency of smoking). Red-haired women did worse than other women in ten health categories and better in only three, being particularly prone to colorectal, cervical, uterine, and ovarian cancer. Red-haired men showed a balanced pattern, doing better than other men in three health categories and worse in three. Number of children was the only category where both male and female redheads did better than other respondents. We also confirmed earlier findings that red hair is naturally more frequent in women than in men. Of the ‘new’ hair and eye colors, red hair diverges the most from the ancestral state of black hair and brown eyes, being the most sexually dimorphic variant not only in population frequency but also in health status. This divergent health status may have one or more causes: direct effects of red hair pigments (pheomelanins) or their by-products; effects of other genes that show linkage with genes involved in pheomelanin production; excessive prenatal exposure to estrogen (which facilitates expression of red hair during fetal development and which, at high levels, may cause health problems later in life); evolutionary recentness of red hair and corresponding lack of time to correct negative side effects; or genetic incompatibilities associated with the allele Val92Met, which seems to be of Neanderthal origin and is one of the alleles that can cause red hair.

Positive association between vocal and facial attractiveness in women but not in men: A cross-cultural study

Various species use multiple sensory modalities in the communication processes. In humans, female facial appearance and vocal display are correlated and it has been suggested that they serve as redundant markers indicating the bearer's reproductive potential and/or residual fertility. In men, evidence for redundancy of facial and vocal attractiveness is ambiguous. We tested the redundancy/multiple signals hypothesis by correlating perceived facial and vocal attractiveness in men and women from two different populations, Brazil and the Czech Republic. We also investigated whether facial and vocal attractiveness are linked to facial morphology. Standardized facial pictures and vocal samples of 86 women (47 from Brazil) and 81 men (41 from Brazil), aged 18-35, were rated for attractiveness by opposite-sex raters. Facial and vocal attractiveness were found to positively correlate in women but not in men. We further applied geometric morphometrics and regressed facial shape coordinates on facial and vocal attractiveness ratings. In women, facial shape was linked to their facial attractiveness but there was no association between facial shape and vocal attractiveness. In men, none of these associations was significant. Having shown that women with more attractive faces possess also more attractive voices, we thus only partly supported the redundant signal hypothesis.

Does age difference really matter? Facial markers of biological quality and age difference between husband and wife

Information conveyed by facial attractiveness markers such as averageness, bilateral symmetry, and secondary sexual characteristics may play an important adaptive role in human sexual selection. Nonetheless, mate choice also relies on other non-physical characteristics such as, for instance, an individual's age. Women prefer and enter in relationships with older partners, whereas in men the inverse relation is observed. Surprisingly, the link between facial morphological markers of biological quality on the one hand and age disparity between partners on the other hand has been as yet subject of very little research. This study aims to fill this gap. We had used facial photographs and demographic data of heterosexual marriages. Facial cues of biological quality, such as averageness, bilateral symmetry, and sexual dimorphism, were digitally measured using geometric morphometric methods and then associated with spouses' age difference. It turned out that a greater age disparity between spouses correlates, in both partners, with higher scores in facial measures which indicate partners' biological quality. One exception is female facial masculinity - generally regarded as an unattractive marker of a low biological quality - which, too, is associated with higher spouse age disparity. In general, our results show that facial symmetry, averageness, and secondary sexual characteristics may play a role in age-dependent mate choice. We suggest that in marriages where the wife is considerably younger than the husband, wife's greater facial masculinity may increase her perceived age and with it, her perceived maturity.

Further evidence for links between facial width-to-height ratio and fighting success: Commentary on Zilioli et al. (2014)

Recent research has reported an association between facial width-to-height ratio (fWHR) and both fighting performance and judgments of formidability in a sample of mixed martial arts (MMA) combatants. The results provide evidence of fWHR being associated with sporting performance and aggression in men. However, it has been argued that the effect of fWHR might be a by-product of associations between body size and behavioral measures. Here we tested whether fWHR is associated with perceived aggressiveness, fighting ability and success in physical confrontation, while controlling for body size, also in a sample of MMA fighters. We found that perceived fighting ability was predicted by weight but not by fWHR. In contrast, both fWHR and body weight independently predicted perceived aggressiveness. Furthermore, we found positive associations between fWHR and fighting performance which appear to be independent of body size. Our findings provide further support for the proposal that fWHR is associated with fighting ability and perceived aggression, and that these effects are independent of body size. Therefore, fWHR might be considered as a viable and reliable marker for inference of success in male intra-sexual competition.

Perceived intelligence is associated with measured intelligence in men but not women

Background

The ability to accurately assess the intelligence of other persons finds its place in everyday social interaction and should have important evolutionary consequences.

Methodology/Principal Findings

We used static facial photographs of 40 men and 40 women to test the relationship between measured IQ, perceived intelligence, and facial shape. Both men and women were able to accurately evaluate the intelligence of men by viewing facial photographs. In addition to general intelligence, figural and fluid intelligence showed a significant relationship with perceived intelligence, but again, only in men. No relationship between perceived intelligence and IQ was found for women. We used geometric morphometrics to determine which facial traits are associated with the perception of intelligence, as well as with intelligence as measured by IQ testing. Faces that are perceived as highly intelligent are rather prolonged with a broader distance between the eyes, a larger nose, a slight upturn to the corners of the mouth, and a sharper, pointing, less rounded chin. By contrast, the perception of lower intelligence is associated with broader, more rounded faces with eyes closer to each other, a shorter nose, declining corners of the mouth, and a rounded and massive chin. By contrast, we found no correlation between morphological traits and real intelligence measured with IQ test, either in men or women.

Conclusions

These results suggest that a perceiver can accurately gauge the real intelligence of men, but not women, by viewing their faces in photographs; however, this estimation is possibly not based on facial shape. Our study revealed no relation between intelligence and either attractiveness or face shape.

Shape differences between the faces of homosexual and heterosexual men

Previous studies have shown that homosexual men differ from heterosexual men in several somatic traits and lay people accurately attribute sexual orientation based on facial images. Thus, we may predict that morphological differences between faces of homosexual and heterosexual individuals can cue to sexual orientation. The main aim of this study was to test for possible differences in facial shape between heterosexual and homosexual men. Further, we tested whether self-reported sexual orientation correlated with sexual orientation and masculinity-femininity attributed from facial images by independent raters. In Study 1, we used geometric morphometrics to test for differences in facial shape between homosexual and heterosexual men. The analysis revealed significant shape differences in faces of heterosexual and homosexual men. Homosexual men showed relatively wider and shorter faces, smaller and shorter noses, and rather massive and more rounded jaws, resulting in a mosaic of both feminine and masculine features. In Study 2, we tested the accuracy of sexual orientation judgment from standardized facial photos which were assessed by 80 independent raters. Binary logistic regression showed no effect of attributed sexual orientation on self-reported sexual orientation. However, homosexual men were rated as more masculine than heterosexual men, which may explain the misjudgment of sexual orientation. Thus, our results showed that differences in facial morphology of homosexual and heterosexual men do not simply mirror variation in femininity, and the stereotypic association of feminine looking men as homosexual may confound judgments of sexual orientation.

Perceived aggressiveness predicts fighting performance in mixed-martial-arts fighters

Accurate assessment of competitive ability is a critical component of contest behavior in animals, and it could be just as important in human competition, particularly in human ancestral populations. Here, we tested the role that facial perception plays in this assessment by investigating the association between both perceived aggressiveness and perceived fighting ability in fighters' faces and their actual fighting success. Perceived aggressiveness was positively associated with the proportion of fights won, after we controlled for the effect of weight, which also independently predicted perceived aggression. In contrast, perception of fighting ability was confounded by weight, and an association between perceived fighting ability and actual fighting success was restricted to heavyweight fighters. Shape regressions revealed that aggressive-looking faces are generally wider and have a broader chin, more prominent eyebrows, and a larger nose than less aggressive-looking faces. Our results indicate that perception of aggressiveness and fighting ability might cue different aspects of success in male-male physical confrontation.

Cross-cultural variation in women's preferences for cues to sex- and stress-hormones in the male face

Women in the UK prefer the faces of men with low levels of the stress hormone cortisol, and the relationship is moderated by the sex hormone testosterone. In a Latvian sample, however, women's preferences were not affected by cortisol, and the interaction with testosterone differed from that of the UK. To further explore cross-cultural variation in preferences for facial cues to sex- and stress-hormones, we tested the preferences of women from 13 countries for facial composites constructed to differ in combinations of the hormones. We found significant relationships between a measure of societal development (the United Nations human development index 2011) and preferences for cues to testosterone in the face, and the interaction between preferences for cues to testosterone and cortisol. We also found a significant relationship between preferences for cues to testosterone and a societal-level measure of parasite stress. We conclude that societal-level ecological factors influence the relative value of traits revealed by combinations of sex- and stress-hormones.

Evolution Born of Moisture: Analogies and Parallels Between Anaximander's Ideas on Origin of Life and Man and Later Pre-Darwinian and Darwinian Evolutionary Concepts

This study focuses on the origin of life as presented in the thought of Anaximander of Miletus but also points to some parallel motifs found in much later conceptions of both the pre-Darwinian German romantic science and post-Darwinian biology. According to Anaximander, life originated in the moisture associated with earth (mud). This moist environment hosted the first living creatures that later populated the dry land. In these descriptions, one can trace the earliest hints of the notion of environmental adaptation. The origin of humans was seen as connected in some way with fish: ancient humans were supposed to have developed inside fish-like animals. Anaximander took into account changes in the development of living creatures (adaptations) and speculated on the origins of humans. Similar ideas are found also in the writings of much later, eighteenth and nineteenth century authors who were close to the tradition of German romantic science. We do not argue that these later concepts are in any way directly linked with those of the pre-Socratics, but they show surprising parallels in, e.g., the hypothesis that life originated in a moist environment or the supposition that human developed from fish-like ancestors. These transformations are seen as a consequence of timeless logic rather than as evolution in historical terms. Despite the accent on the origin of living things, both Anaximander and the later Naturphilosophen lack in their notions the element most characteristic of Darwin's thought, that is, the emphasis on historicity and uniqueness of all that comes into being.

The formation of the theory of homology in biological sciences

Homology is among the most important comparative concepts in biology. Today, the evolutionary reinterpretation of homology is usually conceived of as the most important event in the development of the concept. This paradigmatic turning point, however important for the historical explanation of life, is not of crucial importance for the development of the concept of homology itself. In the broadest sense, homology can be understood as sameness in reference to the universal guarantor so that in this sense the different concepts of homology show a certain kind of "metahomology". This holds in the old morphological conception, as well as in the evolutionary usage of homology. Depending on what is (or was) taken as a guarantor, different types of homology may be distinguished (as idealistic, historical, developmental etc.). This study represents a historical overview of the development of the homology concept followed by some clues on how to navigate the pluralistic terminology of modern approaches to homology.

Semetic rings: towards the new concept of mimetic resemblances

In order to better understand mimicry and similar phenomena, we introduce the concept of seme as means of horizontal (i.e. trans-lineage) transfer of images. Together with horizontal exchange of genes and epigenetic signals, semes complete the triad of powerful channels enabling synchronous communication across the biosphere.