Fluctuating asymmetry and human male life-history traits in rural Belize

Palatal asymmetry assessed by intraoral scans: effects of sex, orthodontic treatment, and twinning. A retrospective cohort study

BACKGROUND

Symmetry is critical in perceived attractiveness, especially in female faces. The palate determines the teeth' alignment and supports facial soft tissues. Therefore, the study aimed to assess the effects of sex, orthodontic treatment, age, and heritability on the directional, anti-, and fluctuational asymmetry in the digital palatal model.

METHODS

The palate of 113 twins, 86 female and 27 male subjects, with and without previous orthodontic treatment, were scanned by the Emerald (Planmeca) intraoral scanner. Three lines were constructed horizontally in the digital model, one between the right and left first upper molars and two between the first molars and incisive papilla. Two observers calculated the left and right angles between the mid-sagittal plane and molar-papilla lines. The intraclass correlation coefficient was used to assess the inter-observer absolute agreement. The directional symmetry was determined by comparing the mean left and right angles. The antisymmetry was estimated from the distribution curve of the signed side difference. The fluctuating asymmetry was approximated from the magnitude of the absolute side difference. Finally, the genetic background was assessed by correlating the absolute side difference between monozygotic twin siblings.

RESULTS

The right angle (31.1 degrees) was not significantly different from the left one (31.6 degrees). The signed side difference followed a normal distribution with a mean of -0.48 degrees. The absolute side difference (2.29 degrees, p < 0.001) was significantly different from zero and negatively correlated (r=-0.46, p < 0.05) between siblings. None of the asymmetries was affected by sex, orthodontic treatment or age.

CONCLUSIONS

The palate illustrates neither directional asymmetry nor antisymmetry, indicating that most people's palates are symmetric. However, the significant fluctuating asymmetry suggests that some subject has considerable asymmetry but is not influenced by sex, orthodontic treatment, age, and genetics. The proposed digital method is a reliable and non-invasive tool that could facilitate achieving a more symmetrical structure during orthodontic and aesthetic rehabilitation.

TRIAL REGISTRATION

The Clinicatrial.gov registration number is NCT05349942 (27/04/2022).

A meta-analysis of the association between male dimorphism and fitness outcomes in humans

Humans are sexually dimorphic: men and women differ in body build and composition, craniofacial structure, and voice pitch, likely mediated in part by developmental testosterone. Sexual selection hypotheses posit that, ancestrally, more 'masculine' men may have acquired more mates and/or sired more viable offspring. Thus far, however, evidence for either association is unclear. Here, we meta-analyze the relationships between six masculine traits and mating/reproductive outcomes (96 studies, 474 effects, N = 177,044). Voice pitch, height, and testosterone all predicted mating; however, strength/muscularity was the strongest and only consistent predictor of both mating and reproduction. Facial masculinity and digit ratios did not significantly predict either. There was no clear evidence for any effects of masculinity on offspring viability. Our findings support arguments that strength/muscularity may be sexually selected in humans, but cast doubt regarding selection for other forms of masculinity and highlight the need to increase tests of evolutionary hypotheses outside of industrialized populations.

Religion and fertility patterns: comparison of life history traits in Catholics and Protestants, Hallstatt (Austria) 1733-1908

Catholicism and Protestantism have different ways of promoting the family unit that could influence survival and fertility at a population level. Parish records in the Austrian village of Hallstatt allowed the reconstruction of Catholic and Protestant genealogies over a period of 175 years (1733-1908) to evaluate how religion and social changes affected reproduction and survival. Life history traits such as lifespan beyond 15 years, number of offspring, reproductive span, children born out of wedlock and child mortality were estimated in 5678 Catholic and 3282 Protestant individuals. The interaction of sex, time and religion was checked through non-parametric factorial ANOVAs. Religion and time showed statistically significant interactions with lifespan >15 years, number of offspring and age at birth of first child. Protestants lived longer, had a larger reproductive span and an earlier age at birth of first child. Before the famine crisis of 1845-1850, Protestants showed lower values of childhood mortality than Catholics. Comparison of the number of children born out of wedlock revealed small differences between the two religions. Religion influenced reproduction and survival, as significant differences were found between Catholics and Protestants. This influence could be explained in part by differential socioeconomic characteristics, since Protestants may have enjoyed better living and sanitary conditions in Hallstatt.

The Changing Face of Beauty: A Global Assessment of Facial Beauty

Beauty is difficult to define. The US population becomes more diverse by the day. Thus, traditional stereotypes of beauty in various ethnic groups become less applicable as diversity increases. Often, new and uniquely beautiful facial features and proportions emerge as different ethnicities converge. With the increased diversity in facial appearance comes increased variability in patients' goals. A successful cosmetic surgeon will cultivate an understanding of aesthetic ideals in different ethnic groups, nurture discussions with patients to determine their aesthetic goals, devise a surgical plan for each patient, and develop and refine the necessary surgical skills to perform the procedure.

The Face of Early Cognitive Decline? Shape and Asymmetry Predict Choice Reaction Time Independent of Age, Diet or Exercise

Slower reaction time is a measure of cognitive decline and can occur as early as 24 years of age. We are interested if developmental stability predicts cognitive performance independent of age and lifestyle (e.g., diet and exercise). Developmental stability is the latent capacity to buffer ontogenetic stressors and is measured by low fluctuating asymmetry (FA). FA is random—with respect to the largest side—departures from perfect morphological symmetry. The degree of asymmetry has been associated with physical fitness, morbidity, and mortality in many species, including humans. We expected that low FA (independent of age, diet and exercise) will predict faster choice reaction time (i.e., correct keyboard responses to stimuli appearing in a random location on a computer monitor). Eighty-eight university students self-reported their fish product consumption, exercise, had their faces 3D scanned and cognitive performance measured. Unexpectedly, increased fish product consumption was associated with worsened choice reaction time. Facial asymmetry and multiple face shape variation parameters predicted slower choice reaction time independent of sex, age, diet or exercise. Future work should develop longitudinal interventions to minimize early cognitive decline among vulnerable people (e.g., those who have experienced ontogenetic stressors affecting optimal neurocognitive development).

Fluctuating body asymmetry in young Polish women in relation to childhood socioeconomic status

The aim of this study was to analyse the relationship between childhood socioeconomic conditions and body asymmetry in young Polish women. The study measured fluctuating asymmetry (FA), which refers to small random deviations from perfect symmetry in bilaterally paired body structures. Data were obtained from 620 female students aged from 19 to 25 years recruited from Jagiellonian University in Cracow, Poland. The research was carried out in the period from January 2016 to May 2017. A composite fluctuating asymmetry (cFA) of the women was calculated using five bilateral body traits. The lengths and widths of the women’s ears, lengths of their 2nd and 4th digits and wrist widths of the right and left sides of the body were measured twice using standard methodology. The following data were collected in a questionnaire: degree of urbanization of the woman’s place of residence during childhood, number of older siblings, parental education and woman’s dominant hand. The results showed a tendency for FA to fall with an increase in parental education, and to rise with an increase in number of older siblings. The level of FA was significantly lower in women from rural areas than in those from cities. The results of the study show that FA in early adulthood is significantly associated with socioeconomic status during childhood, and confirm that the level of FA in adulthood may be a good indicator of stress factors in the early stages of development.

Body symmetry and reproductive hormone levels in women

Fluctuating asymmetry (FA), a morphological marker of developmental stability, may be related to an individual's biological condition, e.g., health or fertility. The aim of this study was to test if the level of a woman's FA was related to her fertility and reproductive potential as measured by reproductive hormone levels. Fifty-three healthy, non-pregnant, naturally cycling women (mean age = 23.42, SD = 1.85 years), participated in the study, conducted in Wrocław (Poland) in May 2015. Early-follicular phase serum levels of anti-Müllerian hormone (AMH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and estradiol (E2) were measured. FA was calculated based on anthropometric measures of six bilateral body traits, and the composite FA index was used in statistical analyses. No relationship was observed between FA and the levels of FSH, LH, and AMH (p > .05), controlled for potential confounders. However, the level of E2 was positively correlated with FA (p < .05). Thus, in young women, FA was not related to hormones levels related to ovarian reserve, but more symmetrical women had lower E2 levels. As FA is an index of developmental stability, environmental, and genetic stress, the results of the study confirm previous research suggesting that developmental conditions may be related to women's endogenous estrogen levels.

Bilateral Asymmetry in Chinese Families with Cleft Lip with or without Cleft Palate

Objective

To determine if Chinese individuals with nonsyndromic cleft lip with or without cleft palate (CL/P) display more bilateral asymmetry than do their unaffected relatives.

Design/Subjects

A case-control study of 313 individuals with CL/P from Shanghai, China, with 201 unaffected relatives as controls.

Methods

Size-adjusted asymmetry scores were defined by data on middle-finger length, palm length, palpebral fissure width, and ear length. Case-control comparisons used a multivariate repeated measures analysis of variance, paired t tests, and the Wilcoxon signed rank test.

Results

The ear-length measure showed a significant increase in fluctuating asymmetry (FA) in individuals with CL/P compared with their unaffected relatives, which was most pronounced in the female cleft lip and palate subgroup (p = .04). No other measures showed any increase in FA.

Conclusion

Evidence was found for increased FA, as measured by overall ear length, in Chinese individuals with nonsyndromic CL/P, compared with their unaffected family members. The use of bilateral measurements other than dermatoglyphics may prove to be a valuable means of assessing overall developmental stability in individuals with developmental malformations and in their families.

Low temperatures during ontogeny increase fluctuating asymmetry and reduce maternal aggression in the house mouse, Mus musculus

Maternal aggression is behavior displayed by post-partum lactating female mice toward unfamiliar conspecifics, presumably as a defense against infanticide. A variety of perinatal stressors can impair maternal care in adulthood. Previous studies on associations between developmental perturbations and maternal aggression have produced mixed results. To address this issue, we employed a proxy for developmental instability, fluctuating asymmetry (FA) to further elucidate the relationship between low temperature stress and maternal aggression. FA, small, random deviations from perfect symmetry in bilateral characters is used as a quantitative measure of stress during ontogeny. Dams were either maintained in standard laboratory temperatures (21 ± 2 °C), or cold temperatures (8 ± 2 °C) during gestation. During lactation, their progeny either remained in the temperature condition in which they were gestated or were transferred to the other temperature condition. Four individual measures of FA, a composite of these measures, and three measures of maternal aggression were assessed in the female progeny in adulthood. Exposure to low temperatures during both pre- and early post-natal development increased composite FA and reduced all three measures of maternal aggression compared to controls. Exposure to low temperatures during the pre- or postnatal period alone did not induce either high FA or altered maternal aggression. Certain measures of FA and nest defense were negatively correlated. Our results suggest that low temperatures experienced during gestation and lactation may have important fitness costs. Low maternal aggression towards infanticidal conspecifics is likely to limit the number of offspring surviving into adulthood. Overall, FA appears to be a reliable indicator of chronic developmental stress with implications for fitness.

Third molar development by measurements of open apices in an Italian sample of living subjects

The aim of this study is to analyse the age-predicting performance of third molar index (I3M) in dental age estimation. A multiple regression analysis was developed with chronological age as the independent variable. In order to investigate the relationship between the I3M and chronological age, the standard deviation and relative error were examined. Digitalized orthopantomographs (OPTs) of 975 Italian healthy subjects (531 female and 444 male), aged between 9 and 22 years, were studied. Third molar development was determined according to Cameriere et al. (2008). Analysis of covariance (ANCOVA) was applied to study the interaction between I3M and the gender. The difference between age and third molar index (I3M) was tested with Pearson's correlation coefficient. The I3M, the age and the gender of the subjects were used as predictive variable for age estimation. The small F-value for the gender (F = 0.042, p = 0.837) reveals that this factor does not affect the growth of the third molar. Adjusted R(2) (AdjR(2)) was used as parameter to define the best fitting function. All the regression models (linear, exponential, and polynomial) showed a similar AdjR(2). The polynomial (2nd order) fitting explains about the 78% of the total variance and do not add any relevant clinical information to the age estimation process from the third molar. The standard deviation and relative error increase with the age. The I3M has its minimum in the younger group of studied individuals and its maximum in the oldest ones, indicating that its precision and reliability decrease with the age.

Men's reproductive investment decisions : Mating, Parenting, and Self-perceived Mate Value

Using questionnaire data completed by 170 men, we examine variation in paternal investment in relation to the trade-off between mating and parenting. We found that as men's self-perceived mate value increases, so does their mating effort, and in turn, as mating effort increases, paternal investment decreases. This study also simultaneously examined the influence on parental investment of men's mating effort, men's perception of their mates' fidelity, and their perceived resemblance to their offspring. All predicted investment. The predictors of investment are also tested independently for men who are still in a relationship with the mother of their children and those that are separated from her. Finally we examine how self-perceived mate value affects how men respond to variation in paternity confidence. Men with a self-perceived low mate value were less likely to respond to lowered mate fidelity by reducing their parental investment compared with men with a self-perceived high mate value.

More symmetrical children have faster and more consistent choice reaction times

Greater cognitive ability in childhood is associated with increased longevity, and speedier reaction time (RT) might account for much of this linkage. Greater bodily symmetry is linked to both higher cognitive test scores and faster RTs. It is possible, then, that differences in bodily system integrity indexed by symmetry may underlie the associations of RT and intelligence with increased longevity. However, RT and symmetry have seldom been examined in the same study, and never in children. Here, in 2 large samples aged 4 to 15 (combined n = 856), we found that more symmetrical children had significantly faster mean choice RT and less variability in RT. These associations of faster and less variable RT with greater symmetry early in life raise the possibility that the determinants of longevity in part originate in processes influencing bodily system integrity early in the life-course.

Recreational Drug Use and Fluctuating Asymmetry: Testing the Handicap Principle

Zahavi's handicap principle suggests that only organisms with good genetic quality can afford to engage in costly behaviors. Recreational drug use can be harmful to one's health and therefore might be viewed as a costly signal of one's genetic quality. One of the measurements of genetic quality is bodily symmetry assessed by fluctuating asymmetry. If unhealthy drug use is a behavioral example of Zahavi's handicap principle, then men who use different stimulants or recreational drugs should be more symmetrical than men who do not use them at all or use them only in low quantity. The aim of this study was to examine the relationships between drug use and fluctuating asymmetry. The subjects were 190 young women and 202 young men. Six bilaterally symmetrical traits were measured: length of II–V digits, wrist breadth, and ear height. Questionnaires included questions about smoking, alcohol drinking, drug use, and designer drug use. There was no relationship between bodily symmetry and smoking frequency, alcohol drinking frequency, drug or designer drug use, total substance use, age of smoking initiation, or reason of this initiation. The results indicate that drug use does not reflect genetic quality and does not necessarily relate to the handicap hypothesis.

Recreational drug use and fluctuating asymmetry: testing the handicap principle

Zahavi's handicap principle suggests that only organisms with good genetic quality can afford to engage in costly behaviors. Recreational drug use can be harmful to one's health and therefore might be viewed as a costly signal of one's genetic quality. One of the measurements of genetic quality is bodily symmetry assessed by fluctuating asymmetry. If unhealthy drug use is a behavioral example of Zahavi's handicap principle, then men who use different stimulants or recreational drugs should be more symmetrical than men who do not use them at all or use them only in low quantity. The aim of this study was to examine the relationships between drug use and fluctuating asymmetry. The subjects were 190 young women and 202 young men. Six bilaterally symmetrical traits were measured: length of II-V digits, wrist breadth, and ear height. Questionnaires included questions about smoking, alcohol drinking, drug use, and designer drug use. There was no relationship between bodily symmetry and smoking frequency, alcohol drinking frequency, drug or designer drug use, total substance use, age of smoking initiation, or reason of this initiation. The results indicate that drug use does not reflect genetic quality and does not necessarily relate to the handicap hypothesis.

Beauty in a multicultural world

The increased demand for facial cosmetic surgery has come from a more diverse, informed, and selective patient population from all walks of life. Virtually no two patients have the same background or cosmetic objectives. However, the classic tenets of beauty including phi, symmetry, averageness, youthfulness, and sexual dimorphism can be applied to persons of all ethnicities to assist in objectifying the abstract concept.

A comparative study of fluctuating asymmetry in Chinese families with nonsyndromic cleft palate

OBJECTIVE

To compare the asymmetry displayed by Chinese patients with nonsyndromic cleft palate (NSCP), their unaffected parents, and a control population.

METHOD

With rigorous inclusion criteria, a total number of 675 individuals with NSCP, 675 parental pairs of these patients, and 650 control individuals were involved in this case-control study. Size-adjusted fluctuating asymmetry (FA) scores were calculated by data on 10 variables. Analysis of variance was used for a three-way comparison of patients/gender-matched parents/gender-matched controls.

RESULTS

A significant increase in FA for ear length (p<.05) was noted in NSCP patients when compared with their gender-matched parents. A significant increase in FA for ear length and palpebral fissure width (p<.05) was observed in NSCP patients when compared with the gender-matched control population. A significant increase in FA for palpebral fissure width (p<.05) was detected in parents of NSCP patients when compared with a gender-matched control population.

CONCLUSION

Our results indicated that, when compared with a gender-matched control population, patients with NSCP show significantly increased FA in both ear length and palpebral fissure width, but the parents of patients with NSCP show significantly increased FA only in palpebral fissure width. In general, these characteristics seem to be more distinct in male individuals.

The influence of symmetry on children's judgments of facial attractiveness

In experiment 1, we examined developmental changes in the influence of symmetry on judgments of attractiveness by showing adults and children pairs of individual faces in which one face was transformed 75% toward perfect symmetry, while the other face was transformed by exaggerating its asymmetries by 75%. Adults and 9-year-olds, but not 5-year-olds, rated the more symmetric faces as more attractive than the less symmetric faces, although the effect was stronger in adults than 9-year-olds. The preference for symmetry was stronger for male than female faces, and stronger for adults' than children's faces. In experiment 2, comparisons of the symmetry of the original male and female faces revealed no measured differences but lower ratings by adults of symmetry in the male faces. Overall, the results suggest that the influence of symmetry on attractiveness judgments emerges after the age of 5 years, and matures after the age of 9 years. The stronger effects for adult viewers may reflect an increase in sensitivity to symmetry as experience with faces increases and/or as the visual system matures. As well, attractiveness may become more salient after puberty, so that honest signals of mate quality, such as symmetry, have a stronger effect for adult viewers, especially when judging adult faces.

Heterosexual romantic couples mate assortatively for facial symmetry, but not masculinity

Preferences for partners with symmetric and sex-typical faces are well documented and considered evidence for the good-genes theory of mate choice. However, it is unclear whether preferences for these traits drive the real-world selection of mates. In two samples of young heterosexual couples from the United Kingdom (Study 1) and the United States (Study 2), the authors found assortment for facial symmetry but not for sex typicality or independently rated attractiveness. Within-couple similarity in these traits did not predict relationship duration or quality, although female attractiveness and relationship duration were negatively correlated among couples in which the woman was the more attractive partner. The authors conclude that humans may mate assortatively on facial symmetry, but this remains just one of the many physical and nonphysical traits to which people likely attend when forming romantic partnerships. This is also the first evidence that preferences for symmetry transfer from the laboratory to a real-world setting.

Fluctuating and directional asymmetry in young human males: effect of heavy working condition and socioeconomic status

Many adverse environmental and genetic factors can affect stability of development during human growth. Although the level of fluctuating asymmetry (FA) may be influenced by environmental and genetic stress encountered during this period, directional asymmetry (DA) is largely attributable to differential mechanical loading during bone growth, for example, handedness. I assessed the effects of heavy working conditions and socioeconomic conditions on asymmetry levels in three groups of young human males: 1) individuals employed in the heavy industry sector (n = 104, mean age = 18.48 +/- 0.61 years), 2) individuals who had the same socioeconomic status as the laborers (n = 102, mean age = 18.39 +/- 0.58 years) but were not laborers, and 3) nonlaborers from the higher socioeconomic levels of society (n = 103, mean age = 18.43 +/- 0.67). For all subjects, hand length, hand width, elbow width, wrist width, knee width, ankle width, foot length, foot width, ear length, and ear width were measured. All measurements of the upper extremities in the labor group appeared to exhibit DA; in the other two groups only hand measurements exhibited DA. According to analysis of FA, subjects living in poor conditions exhibited more FA than their nonlaborer peers living in better conditions. In addition, biomechanical pressures due to heavy working conditions of the labor group appeared to cause increased DA in the upper extremities: DA increased with an increase in the number of years working.

Tall men with medium body fat mass percentage display more developmental stability

A symmetrical body may signal the ability of an individual to cope with developmental perturbations and may thus be considered a 'health certificate'. It is known that symmetrical men are considered more attractive by women and that their reproductive success is higher. This study examined the associations between measures of body structure and fluctuating asymmetry in young Turkish men. Weight, height, and bioelectrical impedance were measured in a sample of 250 men residing in Ankara (mean age=18.4, SD=0.6), and body mass index was calculated. Fluctuating asymmetry was measured using hand length, hand width, elbow width, wrist width, knee width, ankle width, foot length, foot width, ear length, and ear width. According to the obtained findings, there is a negative linear relationship between composite fluctuating asymmetry (CFA) and height, and a positive quadratic relationship between CFA and fat mass. These results might indicate that the tall Turkish men with medium body fat mass percentage display more developmental stability.

A trade-off between early growth rate and fluctuating asymmetry in Brazilian boys

BACKGROUND

Right-left discrepancies in normally symmetrical traits are assumed to result from inability of the individual to buffer environmental and genetic stresses. Fluctuating asymmetry (FA) may therefore signal the quality of an individual to potential mates, or to parents during early life. FA could signal the heritable ability to buffer stress-the 'good genes' hypothesis. Alternatively, FA could signal the degree of within-lifetime exposure to stress, in particular during specific sensitive periods of development--the 'good development' hypothesis.

AIM

We tested the hypotheses that FA at 9 years of age is positively related to (a) fetal growth rate, (b) early infant growth rate, and (c) total post-natal growth rate.

METHODS

FA, weight and height were measured in a sample of 172 boys aged 9 years from Pelotas, Brazil, who had previous measurements of weight and height at birth and 6 months.

RESULTS

Fetal growth was not related to FA, however FA was positively related to total weight gain after birth (p < 0.05). This association could be broadly attributed to weight gain in the first 6 months of post-natal life (p = 0.075). Those currently obese had significantly greater FA than those non-obese (p < 0.05).

CONCLUSIONS

Our results support the 'good development' hypothesis, and suggest that growth rate during an early post-natal critical window, previously linked to numerous health outcomes, also has long-term effects on FA.

Height, Relationship Satisfaction, Jealousy, and Mate Retention

Male height is associated with high mate value. In particular, tall men are perceived as more attractive, dominant and of a higher status than shorter rivals, resulting in a greater lifetime reproductive success. Female infidelity and relationship dissolution may therefore present a greater risk to short men. It was predicted that tall men would report greater relationship satisfaction and lower jealousy and mate retention behavior than short men. Ninety eight heterosexual men in a current romantic relationship completed a questionnaire. Both linear and quadratic relationships were found between male height and relationship satisfaction, cognitive and behavioral jealousy. Tall men reported greater relationship satisfaction and lower levels of cognitive or behavioral jealousy than short men. In addition, linear and quadratic relationships were found between male height and a number of mate retention behaviors. Tall and short men engaged in different mate retention behaviors. These findings are consistent with previous research conducted in this area detailing the greater attractiveness of tall men.

Female Mate Choice is Influenced by Male Sport Participation

Sexual selection theory argues that females invest more heavily in reproduction than males and thus tend to be choosier in terms of mate choice. Sport may provide a context within which females can gain information about male quality to inform this choice. Males may be able to display attractive traits such as athleticism, strength, and physique to females while participating in sport. We predicted that females would favor males that participated in team sports over individual sports and non-athletes because team sport athletes may be more likely to display qualities such as the ability to work well with others and role acceptance. We used a questionnaire, a photograph, and manipulated descriptions to gauge the effects of sport involvement, attractiveness, and status on 282 females' willingness to participate in various types of relationships. Team sport athletes were perceived as being more desirable as potential mates than individual sport athletes and non-athletes. It is suggested that team sport athletes may have traits associated with good parenting such as cooperation, likeability, and role acceptance, and/or these athletes may be better able to assert dominance in a team setting. Results are discussed in terms of further implications and future research.

Fluctuating asymmetry as an animal welfare indicator -- a review of methodology and validity

It has been suggested that fluctuating asymmetry (FA) reflects an animal's ability to cope with the sum of challenges during its growing period and, thus, is a potential welfare indicator. In this review we investigate the evidence of associations between FA and other welfare indicators measured at the level of the individual and of effects of welfare-relevant environmental conditions on FA in populations of captive birds and mammals including humans. As the question of validity cannot be treated independently from the quality of the available data, first a checklist for the proper measurement and analysis of FA is drafted and used to evaluate the methodological quality of the various studies. We recommend this checklist to be used as a standard for future FA studies. We found 17 relevant studies on associations between FA and other welfare indicators, and 36 studies on effects of welfare-relevant factors on FA. Frequent methodological shortcomings or insufficient methodological information allow for only cautious conclusions. The proportion of significant results supporting the link between higher FA and poorer welfare is only moderately high. Independent from statistical significance, almost all studies found the relationship between FA and welfare to be prevailingly in the expected direction. FA is a promising measure of animal welfare, despite a great number of open questions, e.g. relating to the ontogeny of FA or its sensitivity to various stressors. The considerable potential of FA as a welfare indicator makes it worthwhile to pursue more intensely validation studies as well as applied studies. These studies should pay particular attention to an appropriate methodological approach.

Sex similarities and differences in preferences for short-term mates: what, whether, and why

Are there sex differences in criteria for sexual relationships? The answer depends on what question a researcher asks. Data suggest that, whereas the sexes differ in whether they will enter short-term sexual relationships, they are more similar in what they prioritize in partners for such relationships. However, additional data and context of other findings and theory suggest different underlying reasons. In Studies 1 and 2, men and women were given varying "mate budgets" to design short-term mates and were asked whether they would actually mate with constructed partners. Study 3 used a mate-screening paradigm. Whereas women have been found to prioritize status in long-term mates, they instead (like men) prioritize physical attractiveness much like an economic necessity in short-term mates. Both sexes also show evidence of favoring well-rounded long- and short-term mates when given the chance. In Studies 4 and 5, participants report reasons for having casual sex and what they find physically attractive. For women, results generally support a good genes account of short-term mating, as per strategic pluralism theory (S. W. Gangestad & J. A. Simpson, 2000). Discussion addresses broader theoretical implications for mate preference, and the link between method and theory in examining social decision processes.

Attention-deficit hyperactivity disorder and fluctuating asymmetry in another college sample

Attention deficit/hyperactivity disorder (AD/HD) represents a developmental lag that may be reflected in fluctuating asymmetry (FA), i.e., differences from perfect symmetry in traits that display bilateral symmetry. Burton et al. (2003 Am. J. Hum. Biol. 15:601-619) found a statistical trend for FA to increase (as dermatoglyphic index or as total index) as the behavioral measure for AD/HDness (Rasch logit values derived from the Wender Utah Rating Scale, or WURS) increased in males but not in females. The objective here was to do a similar study in an independently collected sample of college students (n = 222; 61 male, 161 female) not selected for AD/HD, looking at FA vs. symptoms for AD/HD based on Rasch versions of responses to the Diagnostic and Statistical Manual of Mental Disorders (DSM IV) (Barkley and Murphy 1998 Attention-Deficit Hyperactivity Disorder, New York: Guilford Press, p. 95-96) and the more comparable shortened WURS. FAs were lowest for body and ear height, and highest for eye width and nose width, and ranged from 0.01 +/- 0.001 (mean +/- SE) for foot and ankle widths to 0.13 +/- 0.01 in eye and nose widths for both sexes; the sexes did not differ significantly. Males displayed higher AD/HD symptom rates overall. There was a significant correlation between body FA and the WURS measure in females after Bonferroni correction (P = 0.002, r(2) = 0.058). Thus, AD/HD symptoms levels increased with an increase in body FA in female college students not selected for AD/HD.

The Pittsburgh Oral-Facial Cleft study: expanding the cleft phenotype. Background and justification

The Pittsburgh Oral-Facial Cleft study was begun in 1993 with the primary goal of identifying genes involved in nonsyndromic orofacial clefts in a variety of populations worldwide. Based on the results from a number of pilot studies and preliminary genetic analyses, a new research focus was added to the Pittsburgh Oral-Facial Cleft study in 1999: to elucidate the role that associated phenotypic features play in the familial transmission patterns of orofacial clefts in order to expand the definition of the nonsyndromic cleft phenotype. The purpose of this paper is to provide a comprehensive review of phenotypic features associated with nonsyndromic orofacial clefts. These features include fluctuating and directional asymmetry, non-right-handedness, dermatoglyphic patterns, craniofacial morphology, orbicularis oris muscle defects, dental anomalies, structural brain and vertebral anomalies, minor physical anomalies, and velopharyngeal incompetence.

Mate choice decisions: the role of facial beauty

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

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

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

The second to fourth digit ratio in elite and non-elite female athletes

Contests in the animal world to determine social status almost exclusively involve males, which points out that androgens may be indispensable in the development of competitive instincts. In animal studies, it has been shown that prenatal exposure to androgens may produce permanent changes toward more aggressive behavior in adulthood. Thus, there is a strong suspicion that women involved in competitive activities, such as sports, may have been exposed to high androgen levels in utero. There is strong evidence that the ratio between the second to fourth digits ratio (2D:4D ratio) correlates negatively with intrauterine androgen concentrations and could potentially be used as a marker for prenatal androgen exposure. Therefore, the purpose of our study was to test the hypothesis that women engaged in sports have lower 2D:4D ratio-a marker of high prenatal androgen exposure. We measured the 2D:4D ratios in elite and non-elite female athletes and compared them with female individuals not engaged in any sport activities. Our results showed that elite female athletes have significantly lower left hand 2D:4D ratios compared to the control group (P < 0.05). Therefore, we can speculate that low 2D:4D ratio may be a positive correlate of sports potential in females.

Symmetry, averageness, and feature size in the facial attractiveness of women

Female facial attractiveness was investigated by comparing the ratings made by male judges with the metric characteristics of female faces. Three kinds of facial characteristics were considered: facial symmetry, averageness, and size of individual features. The results suggested that female face attractiveness is greater when the face is symmetrical, is close to the average, and has certain features (e.g., large eyes, prominent cheekbones, thick lips, thin eyebrows, and a small nose and chin). Nevertheless, the detrimental effect of asymmetry appears to result solely from the fact that an asymmetrical face is a face that deviates from the norm. In addition, a factor analysis indicated that averageness best accounts for female attractiveness, but certain specific features can also be enhancing.

Season of birth and fluctuating asymmetry

Fluctuating asymmetry (FA) refers to random, small deviations from perfect bilateral symmetry in morphological traits. These minor deviations from the ideal phenotype reflect environmental and genetic perturbations experienced during ontogeny. FA has been associated with negative health outcomes and many developmental disorders in humans. The prevalence of developmental disorders and adult health vary according to the month of birth, suggesting that seasonal stressors may leave enduring signs in the adult body, marked by high FA. The current study examined the relationship between FA and birth season. Data were collected for 205 males and females (average age = 20.39 years) on FA of 10 bilateral traits (second, third, fourth, and fifth digit length, palm height, wrist diameter, elbow width, ear height, foot breadth, and ankle circumference). Additional relationships were also investigated among FA, testosterone (T), and birth order. Results indicate that ear FA was lower for fall births compared to winter births in males. In females, palm FA was lower for fall births compared to those of the spring. FA of the digits was positively associated with T in males. Average FA, excluding the digits, decreased as the number of maternal siblings increased for both sexes. T concentrations in males were positively associated with the number of younger brothers. Our results generally confirm previous research on seasonal variation in adult longevity and neurological and psychiatric disorders, suggesting that winter and spring births are at risk for asymmetric developmental trajectory.

Attention-deficit hyperactivity disorder (AD/HD) and fluctuating asymmetry (FA) in a college sample: an exploratory study

Departures from normal development can be partly assessed by measuring fluctuating asymmetry (FA), that is, differences from perfect symmetry in traits that display bilateral symmetry. Attention-deficit hyperactivity disorder (AD/HD), one of the most common psychiatric conditions, is diagnosed if there are developmentally inappropriate levels of inattention, hyperactivity, and impulsivity. The objective here is to measure whether AD/HD behaviors positively correlate with FA in head, hands, and fingerprints of a sample of college students (n = 176, 57 male, 119 female) not selected for AD/HD. FA was measured as the absolute value of the difference between right and left sides divided by group mean trait size. Average FAs (mean, SE) were lowest for finger lengths (e.g., male, 3rd, 0.011 +/- 0.001; female, 3rd, 0.012 +/- 0.001) and highest for digit ridge counts (e.g., male, 5th, 0.075 +/- 0.007; female, 2nd, 0.069 +/- 0.005). Average FAs were similar between the sexes and only one facial measure and the facial index (summed FAs) differed significantly between the sexes (F > M). The scores for measures of the adult AD/HD behavioral assessment instrument, the Wender Utah Rating Scale (WURS) were high overall in this sample and males exhibited higher rates of symptoms than females. A Rasch measurement model analysis of individual responses to the WURS produced a true interval score for each person that is a measure of individual "AD/HDness." FA indices were then regressed on Rasch scores. A univariate analysis of all the variables demonstrated a significant interaction of sex. Hand, Dermatoglyphic, Face, and Total Indices were then regressed by sex on the Rasch values of "AD/HDness." Only in males was there a trend for the Dermatoglyphic Index (F(1,55) = 3.627, P = 0.062) and Total Index (F(1,55) = 3.811, P = 0.056) to increase as AD/HDness increases.