Scientific data and articles about human neurology and biology and their implications on culture, society, personality traits and a sustainable future.
Thursday, September 29, 2016
(Prenatal) testosterone and face morphology
2D:4D ratio and face shape
"We found that [...] (ii) 2D : 4D affects male and female face shape by similar patterns, but (iii) is three times more intense in men than in women."
Males
Visualization of the shape regression on 2D : 4D ratio (averaged among both hands) within males. The middle face with an undeformed square grid is the average landmark configuration and corresponds to the average digit ratio for males. The right grids show deformations from the mean face to faces that are predicted for higher 2D : 4D ratios (0.068=2 s.d. and 0.136=4 s.d., respectively, higher than the average). The left faces correspond to low 2D : 4D ratios (−2 s.d. and −4 s.d.). The ±4 s.d. values are outside the data range.
Shape regression within males on the 2D : 4D ratio of the left hand (upper and lower left figures), the right hand (middle figures), and the mean 2D : 4D ratio (right figures). The three upper figures are visualizations of predicted faces for 2D : 4D ratio 4 s.d. higher than the average. Accordingly, the lower figures are predicted faces for 2D : 4D ratio 4 s.d. lower than the average.
Females
"Although the deformation grids resemble those for males in the figure above, the regression for females is less stable and not significant. Moreover, the shape change predicted for an increase in 2D : 4D ratio is about three times higher in males than in females."
Shape regression within females on the 2D : 4D ratio of the left hand (left figures), the right hand (middle figures), and the mean 2D : 4D ratio (right figures). The three upper figures are visualizations of predicted faces for 2D : 4D ratio 6 s.d. higher than the average. Accordingly, the lower figures are predicted faces for 2D : 4D ratio 6 s.d. lower than the average. (source: Second to fourth digit ratio and face shape, Bernhard Fink, Karl Grammer, Philipp Mitteroecker, Philipp Gunz, Katrin Schaefer, Fred L Bookstein, and John T Manning, Proc Biol Sci. 2005 Oct 7; 272(1576): 1995–2001, Published online 2005 Aug 17. doi: 10.1098/rspb.2005.3179, retrieved July 1st 2016)
Second-to-fourth digit ratio and facial shape in boys: the lower the digit ratio, the more robust the face
"[W]e show a significant relationship between facial shape and 2D : 4D before the onset of puberty [...]. Regression analyses depict the same shape patterns as in adults, namely that the lower the 2D : 4D, the smaller and shorter the forehead, the thicker the eyebrows, the wider and shorter the nose, and the larger the lower face. Our findings add to previous evidence that certain adult male facial characteristics that elicit attributions of masculinity and dominance are determined very early in ontogeny.[...]
[O]ur results show that intermale facial shape variation owing to differences in prenatal testosterone exposure is already present in childhood. One description might be that ‘the effects of [postnatal or adult] circulating hormones are superimposed on changes induced prenatally’. [...]"
Figure 2 (above): Visualization of the shape regression upon 2D : 4D ratio in boys' faces. While the upper panels show thin-plate spline deformation grids from the sample average to predicted facial shapes for several digit ratios, the lower panels visualize the same facial shapes through image unwarping and image averaging. The middle column (with the undeformed grid in upper row) corresponds with the average landmark configuration and the average digit ratio for boys. The faces immediately left and right of the central face show +2 s.d. and −2 s.d., respectively, and the faces at far left and far right show +4 s.d. and −4 s.d., respectively, compared with the average 2D : 4D ratio. Ratios higher than the average 1.09 (+4 s.d.) and 1.04 (+2 s.d.), the faces on the right to lower ones 0.93 (−2 s.d.) and 0.87 (−4 s.d.). Digit ratio accounted for 14.5% of the shape variation. Note that values ± 4 s.d. are outside the observed range.
Figure 3 (above): Superimposed facial shape estimates for various digit ratios (−4 s.d., −2 s.d., average, +2 s.d., +4 s.d.) in boys (n = 17). The darker the line, the smaller the corresponding digit ratio.
Lower testosterone makes thick eyebrows recede and heads become rounder
"Decreasing testosterone levels were noticeable through the changes to the shape of human skulls from the period. Thick eyebrow ridges receded, as heads became rounder."
"Here we provide data on craniofacial feminization (reduction in average brow ridge projection and shortening of the upper facial skeleton) in Homo sapiens from the Middle Pleistocene to recent times. We argue that temporal changes in human craniofacial morphology reflect reductions in average androgen reactivity (lower levels of adult circulating testosterone or reduced androgen receptor densities), which in turn reflect the evolution of enhanced social tolerance since the Middle Pleistocene."
High prenatal testosterone: smaller and shorter foreheads, thicker and lower brows, wider and shorter noses, broader faces (at the cheekbones]), and more prominent chins
"This approach reveals that some aspects of facial masculinity are organized before puberty, suggesting they develop in response to testosterone exposure in utero (Meindl et al. 2012): individuals with lower 2D:4D ratios tend to have smaller and shorter foreheads, thicker and lower brows, wider and shorter noses, broader faces (across the zygomatic arches), and more prominent chins than individuals with higher ratios (Meindl et al. 2012; Schaefer et al. 2005)."
High circulating testosterone in puberty: longer faces, more pronounced brows
"Elevated levels of circulating testosterone beginning at puberty in males, on the other hand, tend to predominately affect facial elongation and brow ridge development. Individuals with higher adult levels of salivary testosterone tend to have superoinferiorly longer faces and more pronounced brows, with brows that are also mediolaterally [=from the middle to the side] expanded (with right and left sides tending toward fusing at midline)—a facial morphology that is absent in the masculinized faces of males with low 2D:4D ratios who do not have elevated levels of circulating testosterone (Schaefer et al. 2005). In males with delayed puberty, treatment with exogenous testosterone has been found to increase upper and total facial height and mandibular ramus and total length but did not affect lower facial height, mandibular body length, or cranial base length (Verdonck et al. 1999). [...] Brow ridge morphology also appears to be important in how people perceive the aggressiveness and trustworthiness of others (Carre´ et al. 2010; Todorov, Baron, and Oosterhof 2008; Xu et al. 2012)."
Puberal testosterone results in longer and broader lower jaw, and sunken narrow eyes
"As a result [of steroid hormones during adolescence], the average adult male has a longer and broader lower jaw than that of a female, and brow ridge growth results in more sunken narrow eyes."
More masculine faces linked to higher testosterone levels after competitive tasks
"after experimentally determined success in a competitive task, men with more a masculine facial structure show higher levels of circulating testosterone than men with less masculine faces."
High prenatal testosterone linked to facial masculinity
"Higher [umbilical] cord testosterone levels were associated with masculinized facial features when males and females were analysed together (...), as well as when males (...) and females (...) were examined separately (...). The relationships remained significant and substantial after adjusting for potentially confounding variables. Adult circulating testosterone concentrations were available for males but showed no statistically significant relationship with gendered facial morphology (...). This study provides the first direct evidence of a link between prenatal testosterone exposure and human facial structure. (...)
GEFS selected five linear (forehead width, nasal bridge length, nasal tip protrusion, upper lip height and nose width) and seven geodesic (intercanthal width, forehead width, outer canthal width, nasal bridge length, nasal tip protrusion, upper lip height and nose width) distances as the most discriminating features between the two sexes. These distances are outlined in figure 3. A mathematical model was generated based on these distances (described in figure 2) and was found to correctly classify male and female faces with 99.47% accuracy.
(...)
A more masculinized face structure has been associated with aggression [48], risk-taking behaviour [49,50] and dominance [51]."
Fig.2 : Creation of the ‘gender score’ for each face.
Fig. 3 : (a) Five Euclidean [2D] and (b) seven geodesic [3D surface] distances that maximally separate males and females in the LDA space.
Low 2D:4D (high prenatal tesosterone) associated with robust and prominent lower face; circulating testosterone with elongated face
"We found some evidence for opposite effects of early androgen action (via 2D:4D ratio) on the upper and the lower face respectively (i.e. low 2D:4D ratio results in a relatively robust and prominent lower face), whereas circulating testosterone seems to cause a rather uniform elongation of the face. Local deformations primarily show pronounced and medially tailed eyebrows for the shapes associated with increasing salivary testosterone. These preliminary results suggest that prenatal and pubertal testosterone have differential effects on male facial shape (...)."
"In our study, we found a negative correlation between the 2D:4D ratio and auricular dimensions. According to the results of our study, the males with a lower 2D:4D ratio (more androgenic men), the length and width of auricles were longer than the other males with higher 2D:4D ratio. In other words, with a decrease in the 2D:4D ratio, the length and width of the auricle increased."
Low 2D:4D ratio associated with higher horizontal facial symmetry in males, and with lower facial symmetry in females
"We measured 2D:4D in a sample of male and female college students and analysed their faces for horizontal asymmetries. 2D:4D was significantly negatively related to facial asymmetry in males, whereas in females facial asymmetry was significantly positively related to 2D:4D. We suggest that digit ratio may thus be considered as a pointer to an individual's developmental instability and stress through its association with prenatal sexual steroids."
In females, masculine faces associated with higher levels of autistic traits; in males, feminine faces associated with higher levels of autistic traits
"Reports linking prenatal testosterone exposure to autistic traits and to a masculinised face structure have motivated research investigating whether autism is associated with facial masculinisation. This association has been reported with greater consistency for females than for males, in studies comparing groups with high and low levels of autistic traits. In the present study, we conducted two experiments by first examining facial masculinity/femininity in 153 neurotypical adults selected for either low, mid-range or high levels of autistic traits. Their three-dimensional facial photographs were subjectively rated by 41 raters for masculinity/femininity and were objectively analysed. In the second experiment, we generated 6-face composite images which were rated by another 36 raters. Across both experiments, findings were consistent for ratings of photographs and composite images. For females, a linear relationship was observed where femininity ratings decreased as a function of higher levels of autistic traits. For males, we found a U-shape function where males with mid-range levels of traits were rated lowest on masculinity. Objective facial analyses revealed that higher levels of autistic traits were associated with less feminine facial structures in females and less masculine structures in males. These results suggest sex-specific relationship between autistic traits and facial masculinity/femininity."
Autistic children and their siblings have masculinized faces (both boys and girls)
Fig.
1: A composite facial image annotated with 13 facial landmarks and a
summary of the landmark names, distances, and distance types measured in
the current study.
Facial landmarks were based on the definitions described in Farkas39.
Landmarks that indicate masculinization:
wider nose base (Sbal-Sbal, between inside of nostrils) and higher nose (N-Sn)
larger upper lip (Sto-Sn, between middle of mouth and underside of nose)
outside of eyes wider apart (Ex-Ex, distance between outside of eyes)
wider (Ft-Ft) and lower forehead (Tr-G)
"Based on the 11 facial distances, the gender classification algorithm correctly classified the sex of the 40 boys and 40 girls with an accuracy of 95.4% for boys and 96.0% for girls. Facial areas were not statistically significantly different between boys and girls (p = 0.12, d = 0.35). Seven of the 11 features were significantly different between boys and girls (see Table 1). Of these, six features (linear alar-base width, linear upper lip height, geodesic outer-canthal width, geodesic forehead width, geodesic nose height, and geodesic upper lip height) were larger in boys than in girls (largest p = 0.01, d = 0.56). Consistent with Tan et al.21, geodesic forehead height was larger in girls than in boys (p < 0.001, d = 1.17).
(...)
The current study provided evidence supporting the hypothesis that facial masculinity would be more pronounced in typically developing boys and girls with a family history of ASD compared to those without. These findings extend our previous work which reported increased facial masculinity among children diagnosed with ASD. Overall, we provide evidence for a broad autism phenotype expressed in facial masculinity among non-autistic siblings of autistic children."
"[T]he autistic boys had significantly lower gender scores for their faces (i.e., more masculine) when compared to the control boys (...). Furthermore, five of the six facial distances were significantly larger in autistic boys than those of control boys. Autistic boys showed larger linear alar-base width, (...), linear nose height (...), linear upper lip height (...), geodesic outer-canthal width (...), and geodesic nose height (...). The difference in geodesic forehead height between boys with and without ASD did not reach statistical significance with the Bonferroni correction (p = 0.02).
(...)
For girls (...) gender scores were significantly lower (i.e., less feminine) for the ASD group compared to the control group (...). Moreover, five of the six facial distances were significantly larger in autistic girls compared to control girls [(identical to boys above)]. Geodesic forehead height was comparable for girls with and without ASD (...).
(...)
The distributions of the gender scores for the four groups of children included in this study [show] a clear leftward (more masculine) shift in the distributions for the autistic girls and boys compared to their typically developing same-sex counterparts.
(...)
[A]utistic boys with more masculine overall facial morphology had more severe ASD presentations relating to social communication. (...)
[A]utistic girls with less feminine facial structure presented with more pronounced difficulties in social communication."
The present findings provide support for the hypermasculinisation account in which increased facial masculinity was observed in the overall facial structure and in individual features of autistic boys and girls in comparison to typically-developing controls."
Facial traits linked to low 2D:4D of Buryats are partly reversed to those of Europeans.
"The results revealed that 2D:4D was associated with facial morphology in Buryat men, and to a lesser extent in women. Narrower faces, elongated in the vertical direction, and a narrower lower facial outline, were characteristic of Buryat men with low 2D:4D ratios, which corresponded to the male-like facial shapes in Buryats."
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