Second-to-fourth digit ratio and facial shape in Buryats of Southern Siberia

Abstract

Background The 2nd-to-4th digit ratio (2D:4D) is a putative predictor of a prenatal exposure to sex hormones. 2D:4D is sexually dimorphic (males < females). Studies, linking digit ratio and full facial shapes among Europeans, show that a low 2D:4D is associated with a set of male-specific facial features. Buryats – Mongolian people from Southern Siberia – demonstrate a different pattern of facial sexual dimorphism than Europeans (narrower and more vertically elongated faces in men as opposed to women). Aim The aim of the present study was to investigate the association between facial shape and the 2D:4D in comparison to the pattern of facial sexual dimorphism in Buryats. Subjects Buryats: 88 men and 80 women aged 20 ± 2 years. Outcome measures To assess relationship between facial shape and 2D:4D we used a geometric morphometric approach based on standardized full-face frontal photographs and direct measurements of the digit lengths among right-handed individuals. Results 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. Conclusions In Europeans, such facial features were reported for men with a high 2D:4D, which corresponded more to female-like European facial shapes. Hence, our results show that sex-specific morphogenesis in humans is multidirectional, and that digit ratio is capable of predicting sex-specific facial traits even in populations with differing sexually-dimorphic morphology.

Facial and body sexual dimorphism are not interconnected in the Maasai

“…In this study, it was demonstrated that sexual facial dimorphism in Maasai is rather low, compared to Europeans and Asians [ 38 , 124 ], and sex explains 1.8% of the total variance of facial shape in the whole sample (for instance, in Buryats, a Mongolian population of Southern Siberia, sex explains 20% of the total facial shape variance, which was demonstrated using the same configuration of facial landmarks as in the present study [ 124 ]). When the three age cohorts of Maasai were tested separately, it was found that sex differences in facial morphology were minimal (2%) in the youngest age cohort, and increase with age, gaining up to 4% in in elder-adults age cohort.…”

“…Seventy-one facial landmarks and semi-landmarks were manually placed on each photograph using tpsDig2 2.17 [ 123 ]. Landmarks’ positions were set based on the configuration developed by Windhager et al [ 45 ], which has been already used in our earlier studies [ 37 , 121 , 124 ]. This configuration included 37 landmarks, which are known to be classical anthropometrical approximations to cranio-facial and soft-tissue facial shape determinants [ 33 , 45 , 66 , 125 , 126 ] as well as 34 semilandmarks, used for covering facial outline, eye-brows and lips shapes.…”

Perception of Emergent Leaders’ Faces and Evolution of Social Cheating: Cross-Cultural Experiments

“…Seventy-one anthropometric facial landmarks and semilandmarks were placed on each of the selected photographs in tpsDig 2. 17 (Rohlf, 2015) following configuration developed by Windhager et al (2011), and used previously in our earlier studies (Butovskaya et al, 2018;Rostovtseva et al, 2020aRostovtseva et al, , 2021aRostovtseva et al, , 2021b. The facial configurations were then standardized for the position, orientation, and scale using Generalized Procrustes superimposition with sliding of the semi-landmarks in tpsRelw 1.67 (Rohlf, 2015).…”

Cross-Cultural Differences in Perception of Facial Trustworthiness Based on Geometric Morphometric Morphs

“…Faces perceived as untrustworthy had more V-shaped eyes and brows positions (a frown), were more prolonged in vertical direction, had narrower facial outline, especially in the lower face. Generally, the facial shape pattern along trustworthy–untrustworthy vector almost fully corresponded to the facial femininity-masculinity vector for Buryats (see Rostovtseva et al, 2021b; Rostovtseva, Mezentseva, et al, 2020). Earlier studies conducted among representatives of European populations, also demonstrated that facial shape perceived as more trustworthy is female-like (Kleisner et al, 2013; Rostovtseva et al, 2023; Stirrat & Perrett, 2010).…”

“…This caused further exclusion of female photographs from the analysis, and the rest of our study focused only on the male part of the Buryat sample, and only on the male-male facial perception. The lack of association between female facial shape and independent biological or behavioral parameters is a very common situation (Mezentseva et al, 2023; Rostovtseva et al, 2021a; Rostovtseva, Mezentseva, et al, 2020). One of the possible reasons for that may be rooted in less general variability in female facial shape compared with male, due to variability in testosterone-mediated facial traits, which is much higher in men.…”