Ekrami Omid, Claes Peter, Van Assche Ellen, Shriver Mark D, Weinberg Seth M, Marazita Mary L, Walsh Susan, Van Dongen Stefan
Evolutionary Ecology Group, Department of Biology, University of Antwerp, 2610 Antwerp, Belgium.
Department of Electrical Engineering, ESAT/PSI, KU Leuven, 3000 Leuven, Belgium.
Symmetry (Basel). 2021 Feb;13(2). doi: 10.3390/sym13020304. Epub 2021 Feb 10.
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.
In this study, we examined a large dataset of high-density 3D facial scans of 1260 adults (630 males and 630 females). We mapped a high-density 3D facial mask onto the facial scans in order to obtain a high number of quasi-landmarks on the faces. 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. The possible correlation between these two qualities was then examined using Pearson's coefficient and Canonical Correlation Analysis.
We 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.
Our results question the idea that fluctuating asymmetry and masculinity should be (more strongly) correlated in men, which is in line with the recent literature. Future studies should possibly focus more on the evolutionary relevance of the observed correlation in women.
波动不对称性常被用作发育不稳定性的指标，并被认为是基因质量的信号。雄激素水平高直接导致的显著男性化表型特征的展现，也被视为基因质量的标志，因为这些激素可能起到免疫抑制剂的作用。因此，波动不对称性和男性化特征预计会共同变化。然而，文献中缺乏关于这一假设的有力证据。
在本研究中，我们检查了1260名成年人（630名男性和630名女性）的高密度3D面部扫描的大型数据集。我们将一个高密度3D面部模板映射到面部扫描图像上，以便在面部获得大量的准地标点。使用主成分分析从地标点中提取波动不对称性的多维测量值，并使用偏最小二乘法为每张脸获得男性化/女性化分数。然后使用皮尔逊系数和典型相关分析来检验这两种特征之间可能的相关性。
我们发现男性的波动不对称性和男性化特征之间没有相关性。然而，在女性中，平均波动不对称性与男性化特征之间发现了微弱但显著的相关性，其中女性化的脸平均具有更高水平的波动不对称性。这种相关性可能指向基因质量是不对称性和男性化特征的潜在机制；然而，它也可能由其他健康或生活史特征驱动，例如生育能力。
我们的结果对男性的波动不对称性和男性化特征应该（更强地）相关这一观点提出了质疑，这与最近的文献一致。未来的研究可能应该更多地关注观察到的女性相关性的进化意义。
