by Neil Caton, Samuel Pearson, & Barnaby Dixon
The presence of dedicated pre-registered replication submissions in peer-reviewed journals is important for maintaining and improving the self-correcting tendency of the scientific enterprise. Replications inform us when we have (un)knowingly been led astray, and given the alarmingly high rates of false positives found in psychology to date, it is clear that we need more replications if the field is to continue separating the wheat from the chaff.
We recently conducted a pre-registered replication of a popular and influential study by Třebický et al. (2013) that was published in Psychological Science. This was the first study to provide scientific evidence for the claim that the same facial features are associated with both real-world fighting success and dominance judgments. Třebický and colleagues were the first to use Ultimate Fighting Championships data in the psychological sciences – a novel, creative, and unique idea. They correlated the entire facial morphology of UFC fighters’ with their fighting success and perceived aggressiveness. Men’s facial features predicted their actual fighting success, and participants could unconsciously perceive their fighting success simply by looking at their face. In our eyes, this is an important finding using a creative methodology that provides the first evidence in support of the claim that the face may be shaped by intrasexual selection—a long-standing debate in evolutionary face research.
Our acclaim for Třebický et al. (2013) led us to read the paper multiple times. Over those readings, several of study’s methodological details struck us as a cause for concern, and hence, formed the rationale for our decision to pursue a replication. Firstly, the association between facial shape and fighting success was found only in the combined sample of 19 light heavyweight and 14 heavyweight fighters. Second, Třebický and colleagues excluded certain groups of participants (e.g., men with moustaches and beards, Africans and Asians) prior to analysis, and the results were slightly under the significance threshold. There was no explanation for these exclusions in the original paper, likely owing to the tight word restrictions of Psychological Science at the time. Finally, Třebický and colleagues examined which facial structures were associated with actual fighting success and perceived aggressiveness, but not those associated with perceived fighting ability. While Třebický and colleagues examined the facial traits associated with fighting success, this doesn’t necessarily mean that participants perceived these traits as cues to fighting success (particularly when considering that Třebický and colleagues found that perceived ability did not significantly predict actual fighting ability). Overall, we acknowledge that Třebický et al. (2013) was the first study on the topic, and therefore there was no standardised process at the time for this creative and novel methodology.
To form the dataset for our replication project, we collected fight statistics, body composition and morphology, demographic information, and photos of 516 male fighters in the Ultimate Fighting Championship. We attached 36,636 facial landmarks to these 516 faces. We then collected data from 1,000 United States-based online raters to judge these 516 faces on perceived aggressiveness and fighting ability.
Consistent with the original study, we found that men with masculine facial features (e.g., large nose, deep-set eyes) were seen as more aggressive, independent of their body size. We also found novel evidence that men with masculine facial features were seen as better fighters, which was because these men were seen as being bigger overall. These analyses between facial shape and perceived fighting ability were not performed in the original study, but was our novel extension of the original study. We did not find an association between facial structure and fighting success. There could be several reasons for this non-significant association: the UFC contains the best fighters in the world, mixed-martial-arts competitions are often legally and ethically required to have weight categories, and/or win percentage may not be an ideal reflection of pure fighting success. If men with masculine facial features are seen as better fighters because they’re bigger overall, then men’s masculine facial features could predict their fighting success in the few championships that don’t have weight restrictions—not because the face predicts fighting success in itself, but because men with bigger faces are bigger overall.
Strikingly, we often found negative relations between perceived aggressiveness and fighting ability on overall win percentage (i.e., more successful fighters were perceived as less successful and aggressive). Třebický et al. (2013) noted some excellent points in their discussion section that we consider to be of importance here, one of which was postulating that human psychological systems track force output. To echo their suggestions, it could be that human psychological systems positively track knockout power but negatively track the other avenues to victory, such as submission and decision victories, leading to an overall negative association.
Overall, our results support the original Třebický et al. (2013) study in some ways but not in others. Humans may have evolved psychological mechanisms to aid in assessments of aggressiveness or competitive tendency, however they do not support the argument that structural facial cues are honest indicators of competitive ability.