Neither facial aggressiveness nor facial width to height ratio are related to fighting success Thomas Richardson, Anam Bhutta, Elena Bantoft, R. Tucker Gilman Abstract There is a growing consensus that there is information in a man’s face about how formidable (big and strong) he is. Recent work in mixed martial artists has shown that there may be facial correlates of fighting success. Fighters with more aggressive looking faces, as well as higher facial width to height ratios (fWHR), win a greater percentage of their fights. This has been used as evidence that human males may have evolved to signal and detect formidability using facial features. However, all previous studies have used datasets that may have considerable overlap, so it is important to replicate these effects in new samples. Moreover, some studies show that facial width to height ratio is correlated with body size, which may have confounded associations between fWHR and fighting success. The present study attempted to replicate and expand previous findings in 3 samples totalling several hundred professional fighters taken from several combat sporting leagues. I also tested whether head tilt affected ratings of aggressiveness, as previous studies have found conflicting effects. Overall, I found no significant links between fighting success and fWHR or facial aggressiveness. Tilting the head up or down both made a fighter’s face look more aggressive. Interestingly, there was only low- moderate agreement between raters on the apparent aggressiveness of a given face. Further, I found that facial width to height ratio was related to body size, and that body size mediated the link between fWHR and perceived aggression. This work casts doubt on several theories that argue the human face evolved to show fighting prowess and threat. 49 There is a growing consensus that human males have been sexually selected for contest competition, particularly of the violent variety (Puts 2010, Sell et al., 2012; Puts et al., 2016; Plavcan, 2012). Physical violence, murder, and war are (and have always been) near- exclusively perpetrated by men, across all studied cultures (Adams 1983). The archaeological record contains substantial evidence of male-on-male violence (Keely, 1996; Walker, 2001). Violence and war are thought to have been extremely common in our hunter-gatherer past, with as many as 30% of males dying through violence (Keely, 1996; LeBlanc et al., 2003; Guilane and Zammit, 2008; Gat, 2008; Pinker 2012; Walker and Bailey, 2013; Gat 2015). Most of this violence was intergroup, rather than intragroup, though both are significant (Wrangham, 2018). Consequently, human males have been sexually selected to be formidable. An individual’s formidability (sometimes called ‘physical dominance’) is determined by their ability to inflict physical damage on other humans. Formidability is typically operationalised using measures such as height, weight, muscle mass, and direct measures of strength (Blaker and Van Vugt, 2014). Humans show such large sexual dimorphism in facial features that we can tell whether someone is biologically male or female from a picture of their face with over 95% accuracy (Burton et al., 1993). This is likely to be a consequence of sexual selection, but whether the differences are driven by change in the male or female face is not entirely clear. Male facial masculinity is unlikely to be explained by intersexual selection (i.e., female choice), because females do not consistently find masculine faces attractive (Scott, et al., 2014). Female facial femininity on the other hand is strongly and consistently attractive to males (reviewed in Little et al., 2011). Male faces may have been modified by selection to protect their eyes, brains and breathing apparatus (nose and mouth) in fights (Carrier and Morgan, 2015). Many studies show that a man’s face shape contains information about how formidable he is. Sell et al., (2009) asked individuals from several countries to judge the relative strength of men from only photos of their faces. They found that these judgements correlated with the men’s upper body strength. Other studies have also found facial correlates of upper body strength (Butovskaya et al., 2018; Fink et al., 2007; Han et al., 2017; Holzleitner & Perrett, 2016; but see van Dongen et a., 2014). Promisingly, these studies have found similar results in WEIRD (western, educated, industrialised, rich and democratic) and non-WEIRD societies (see Sell et al., 2009 and Butovskaya et al., 2018 for non-WEIRD evidence). Other work has found that there is information about a man’s height in his facial features (Holzleitner et al., 2014; von Borell et al., 2019; Zaidi et al., 2019). 50 Additionally, a fascinating study by Třebický et al., (2013) found that there may be cues to a man’s fighting ability in his face. By studying mixed martial arts (MMA) fighters, they could obtain relatively well-standardised facial photos and direct measures of fighting success (percentage of fights won). They had participants’ rate how aggressive a fighter’s face looked, obtaining a measure of ‘facial aggressiveness’. They found that a fighter’s facial aggressiveness was positively correlated with fighting success. On the other hand, when participants were asked to judge how good a fighter was just based on his face, they found this did not correlate with actual fighting ability. A follow-up study by Little et al., (2015) found that participants could predict the winner of MMA bouts better than chance despite only being shown pictures of the fighter’s faces. It should be noted that the faces were taken from the same fighting league (The Ultimate Fighting Championship or UFC) as in Třebický et al., (2013) but 1 year later, so there will be overlap between the datasets. However, Třebický et al., (2019) failed to replicate the original effect of Třebický et al., (2013) in a smaller sample of 44 Czech amateur MMA fighters. Indirect evidence supporting a link between fighting ability and face shape was also found by Doll et al., (2014). They asked raters to judge how good a fighter a man appeared looking just at his facial photo. They found this rating correlated with ratings of fighting ability given by a man’s friends. However, Doll et al., did not record whether a man’s friends had actually seen him fight before, so it is unclear whether ratings of fighting ability made by friends have any objective basis. Other masculine facial traits, such as beardedness, may not be related to fighting success (Dixson et al., 2018). It is unclear whether associations between facial features and fighting ability are the result of men having evolved to signal their fighting ability through their face, or whether participants simply learn the facial features associated with formidability over time. Another pair of studies found that the facial width to height ratio (fWHR) is also associated with fighting ability. Defined as the width of the cheekbones divided by height of the lower face, fWHR is thought to be an evolved signal of aggression and threat (see Geniole et al., 2015 and Haselhuhn et al., 2015 for reviews). In support of this Zilioli et al., (2015) found in a sample of 245 UFC fighters that fWHR was related to percentage of fights won, once total number of fights was controlled. In a second study they found a large positive correlation between fWHR and perceived facial ‘toughness’. Třebický et al., (2015) replicated this effect using the sample of faces taken from Třebický et al., (2013), and also showed that fWHR correlated with facial aggressiveness. They did not test whether fWHR mediated the link between facial aggressiveness and fighting success, though this seems a plausible hypothesis. 51 Currently, psychology (along with much of science) is in the midst of a ‘replication crisis’. Many effects often fail to appear when researchers repeat the original studies in new samples. Several large-scale collaborations have been conducted, where multiple labs attempt to directly replicate cherished findings using larger samples. These ‘Many Labs’ projects have revealed that as many as half of the findings they test do not replicate consistently (Open science collaboration, 2015; Ebersole et al., 2016; Klein et al. 2018). As such researchers are returning to foundational and influential studies and attempting to replicate them. This paper is one of those attempts. One potential cause for concern with the studies above is that the original studies (Třebický et al., 2013; Zilioli et al., 2015) and their replications used overlapping datasets. As fighters (not raters) are the units of analyses in these studies, this is equivalent to replicating a study using a sample that includes many of the same participants as the original study. This can be problematic as it means results are not independent of each other. Indeed, nearly all studies exploring how fighting ability is associated with face shape use samples that may overlap considerably. Třebický et al., (2013; 2015), Little et al., (2015) and Zilioli et al., (2015) all used data collected from UFC fighters over a period of around 1 year (June 2011- September 2012). Fighters enter and leave the UFC fairly often, but few fighters are likely to last less than a year. This raises the possibility that the results reviewed above are the consequence of the specific dataset they all used. To remedy this, I attempted to replicate these effects in 3 fighting leagues with little or no overlap with the UFC. Finally, some studies have indicated that the way a person tilts their head may influence how they are perceived. Some studies find that tilting the head down increases perceptions of dominance and masculinity (Hehman, et al., 2013; Toscano, et al., 2018; Witkower & Tracy, 2019; Torrance et al., 2020), while others find tilting the head up increases dominance perceptions (Mignault & Chaudhuri, 2003; Bee, et al., 2009; Burke & Sulikowski, 2010).