Lack of support for the association between facial shape and aggression: a reappraisal based on a worldwide population genetics perspective

Abstract

Antisocial and criminal behaviors are multifactorial traits whose interpretation relies on multiple disciplines. Since these interpretations may have social, moral and legal implications, a constant review of the evidence is necessary before any scientific claim is considered as truth. A recent study proposed that men with wider faces relative to facial height (fWHR) are more likely to develop unethical behaviour mediated by a psychological sense of power. This research was based on reports suggesting that sexual dimorphism and selection would be responsible for a correlation between fWHR and aggression. Here we show that 4,960 individuals from 94 modern human populations belonging to a vast array of genetic and cultural contexts do not display significant amounts of fWHR sexual dimorphism. Further analyses using populations with associated ethnographical records as well as samples of male prisoners of the Mexico City Federal Penitentiary condemned by crimes of variable level of inter-personal aggression (homicide, robbery, and minor faults) did not show significant evidence, suggesting that populations/individuals with higher levels of bellicosity, aggressive behaviour, or power-mediated behaviour display greater fWHR. Finally, a regression analysis of fWHR on individual's fitness showed no significant correlation between this facial trait and reproductive success. Overall, our results suggest that facial attributes are poor predictors of aggressive behaviour, or at least, that sexual selection was weak enough to leave a signal on patterns of between- and within-sex and population facial variation.

Figure 1. Sexual dimporphism on fWHR and further cranial indices.

Box and whisker plots of global sexual dimorphism computed across the different databases. Indices that differed significantly among sexes (after t-test for independent samples) are shown in solid grey. A) Howells database; b) Pucciarelli database, c) 2D Geometric Morphometric database, d) 3D Geometric Morphometric database, e) Patagonian groups database. Square: median; box: 25%–75%; whisker: minimum-maximum values.

Figure 2. Sexual dimporphism on fWHR across socio-cultural categories.

Box and whisker plots of a) fWHR sexual dimorphism in samples belonging to three different socio-cultural categories: HG: hunter-gatherers; F: farmers; SS: state societies. b) fWHR values of males from the Mexican general population (GP), males prosecuted by homicide (H), robbery (R) and other minor faults (O). Square: mean; box: standard error; whisker: standard deviation. c) Regression of fWHR on fitness, estimated as lifetime reproductive success (LRS, number of children raised to adulthood).