Department of Anthropology, Istanbul University, Istanbul, Turkey.
Department of Evolutionary Anthropology, University of Vienna, Vienna, Austria.
Am J Hum Biol. 2024 Nov;36(11):e24155. doi: 10.1002/ajhb.24155. Epub 2024 Sep 12.
Human sexual dimorphism in physical strength manifests itself in men having a greater muscle mass than women, reflecting ancestral roles in competition, protection, and provisioning. Prenatal testosterone exposure, approximated via the second-to-fourth digit ratio (2D:4D), is linked to increased muscular strength in both sexes, indicating a developmental influence. Previous research has shown that both physical strength and 2D:4D have facial shape correlates, especially in men, but most studies have focused on Western populations and one trait. We therefore hypothesized a broader relationship between facial shape and both physical strength and 2D:4D.
In this study, we quantified the association between facial shape, handgrip strength (HGS), and 2D:4D in a non-Western Turkish sample (72 men, 55 women; Md = 22 y, SIR = 1.8 y) using two dimensional geometric morphometrics. Thirty-eight somatometric and 32 semi-landmarks were digitized on facial photographs taken in frontal view. Physical strength was assessed via handgrip strength (HGS), and the second digit length was divided by the fourth digit length to calculate 2D:4D.
Both HGS and 2D:4D were significantly associated with shape in both sexes, but only in men did they explain a significant amount of facial variation. Thin-plates spline deformation grids and geometric morphometric morphs visualized the facial shape changes related to variations in handgrip strength, 2D:4D, and sexual dimorphism, enabling trait comparisons.
This study contributes a comparative sample from the Middle East, which is indispensable to discern universalities from Western peculiarities. It provides evidence to better understand the biological basis of facial traits, which can potentially serve as increasingly relevant social cues in today's online and digital environments.
男性的体力比女性更强，这种人体的性别二态性表现在肌肉质量上，反映了祖先在竞争、保护和供应方面的角色。通过第二到第四指骨长度比（2D:4D）来近似估计胎儿期的睾丸激素暴露，与两性的肌肉力量增加有关，表明其具有发育影响。先前的研究表明，身体力量和 2D:4D 都与面部形状有关，尤其是在男性中，但大多数研究都集中在西方人群和一个特征上。因此，我们假设面部形状与身体力量和 2D:4D 之间存在更广泛的关系。
在这项研究中，我们使用二维几何形态测量法，在一个非西方的土耳其样本（72 名男性，55 名女性；Md=22 岁，SIR=1.8 岁）中，量化了面部形状、握力（HGS）和 2D:4D 之间的关联。38 个体测标志和 32 个半标志被数字化到正面拍摄的面部照片上。通过握力（HGS）评估体力，第二指长度除以第四指长度来计算 2D:4D。
HGS 和 2D:4D 在两性中都与形状显著相关，但只有在男性中，它们才能解释大量的面部变异。薄板样条变形网格和几何形态学形态可视化了与握力、2D:4D 和性别二态性变化相关的面部形状变化，使特征比较成为可能。
本研究提供了从中东获得的比较样本，这对于辨别西方特殊性中的普遍性是不可或缺的。它提供了证据，以更好地理解面部特征的生物学基础，这些特征在当今的在线和数字环境中可能作为越来越相关的社会线索。
