Fluctuating Asymmetry and Sexual Dimorphism in Human Facial Morphology: A Multi-Variate Study

• NCJ Number: 304134
• Author(s): Omid Ekrami; et al
• Date Published: 2021
• Grant Number(s): 2015-R2-CX-0023; 2014-DN-BX-K031; 2008-DN-BX-K125
• Agencies: NIJ-Sponsored

Annotation

This study examined a large dataset of high-density 3D facial scans of 1,260 adults (630 males and 630 females), mapping a high-density 3D facial mask onto the facial scans in order to obtain a high number of quasi-landmarks on the faces; and multi-dimensional measures of fluctuating asymmetry were extracted from the landmarks using Principal Component Analysis, and masculinity/femininity scores were obtained for each face using Partial Least Squares, followed by an examination of the possible correlation between these two qualities, using Pearson’s coefficient and Canonical Correlation Analysis.

Abstract

Fluctuating asymmetry is often used as an indicator of developmental instability and is proposed as a signal of genetic quality. The display of prominent masculine phenotypic features, which are a direct result of high androgen levels, is also believed to be a sign of genetic quality, as these hormones may act as immunosuppressants. Fluctuating asymmetry and masculinity are therefore expected to covary; however, there is lack of strong evidence in the literature regarding this hypothesis. The current study found no correlation between fluctuating asymmetry and masculinity in men; however, a weak but significant correlation was found between average fluctuating asymmetry and masculinity in women, in which feminine faces had higher levels of fluctuating asymmetry on average. This correlation could possibly point to genetic quality as an underlying mechanism for both asymmetry and masculinity; however, it might also be driven by other fitness or life history traits, such as fertility. The study concludes that its findings challenge the prevalent concept in recent literature that fluctuating asymmetry and masculinity should be (more strongly) correlated in men. Future studies should possibly focus more on the evolutionary relevance of the observed correlation in women. (publisher abstract modified)