No link found between facial shape and aggression

The professor Mireia Esparza, from the Anthropology Section of the Department of Animal Biology of the University of Barcelona, is part of the international research group who carried out this study. The research is coordinated by the experts Rolando González José, from the Patagonic National Centre (CENPAT-CONICET, Argentina) and Jorge Gómez Valdés, from the National Autonomous University of Mexico.

Sample of about 5,000 individuals from 94 worldwide human populations

The study provides new scientific data to reject the hypotheses that associate facial shape with antisocial and criminal behaviours, which attained its maximum splendour during the mid-19th century and lately have been revitalized. To carry out the study, researchers used a sample of 4,960 individuals from 94 worldwide populations. This large sample allowed to get a global estimation of facial shape and to develop an accurate analysis taking into account distinguishing traits. The experts based the research on the study of the fWHR -- facial width-to-height ratio -- as a possible predictor of aggressive behaviours in men populations.

According to the professor Mireia Esparza, "fWHR was used for two main reasons: on one hand, it is a good indicator of face shape and, on the other hand, it was used in those previous studies which established a correlation between higher fWHR scores and aggression. By this way, we were able to compare results without any bias caused by the use of any other indicator." Esparza contributed to this international study by reconstructing the genealogies of the Hallstatt population from biodemographic data to get genealogical information of the skulls studied and estimate the fitness of each individual analysed.

Craniofacial measurements and 2D and 3D cranial landmark coordinates

Research's results support previous studies which do not prove any relation between fWHR and aggression. "This study goes more deeply," remarks Mireia Esparza. "The methodology used is based on craniofacial measurements and 2D and 3D cranial landmark coordinates, so it provides us with more accurate results than other previous studies based on photographs analysis. Moreover, our research used a large sample of about 5,000 individuals from 94 worldwide populations, so we were able to carry out inter and intra-population comparisons."

"Finally -- she continues -- , two specific databases, one sample of male prisoners of the Mexico City Federal Penitentiary and one the skulls from the catholic church of Hallstaff, Austria, enabled a deeper analysis. The Hallstatt database was used to estimate the correlation among life history parameters, such as fitness or reproductive success, and skull shape traits; this sample has been essential to yield that there is not significant correlation between fWHR and male fitness in this population. The Mexican database demonstrated that fWHR is not significantly greater on those males involved in aggressive crimes in comparison with the general population."

Neither more violence, nor more reproductive success

According to the coordinators of the study, the experts Rolando González José and Jorge Gómez Valdés, "the social and political implications that this kind of non-contrasted adaptive hypotheses could have, may increase racial prejudices, discrimination and intolerance." Besides demonstrating that facial traits are a poor predictor of aggressive behaviours, the study also proves that fWHR is unrelated to sexual dimorphism. In other words, males who present higher fWHR values -- wide faces in comparison with their height -- do not have a greater reproductive success or show more violent behaviours. If males displaying higher fWHR scores achieved better fitness values, it would trigger a process of sexual selection focused on fWHR. "Our study proves that there is not statistical association between fWHR and male fitness, and that facial shape is not a good predictor of behaviour," concludes Esparza.