Geniole, Shawn; Department of Psychology
      As do many species, humans visually assess the ability and propensity of others to cause trouble or harm (threat potential), although the mechanisms that guide this ability are unknown. One potential mechanism that may underlie advertisements and assessments of threat is the facial width-to-height ratio (face ratio). The overarching goal of this thesis was to test both the ecological validity of the face ratio (i.e., the extent to which it maps onto an individual’s actual threat potential), and its utility in influencing observers’ first impressions of traits related to threat potential. In Chapter 2, I found that men (n = 146) but not women (n = 76) with larger face ratios were more likely to cheat in a lottery for a cash prize than were men with smaller face ratios. In Chapter 3, to better identify the precise social function of the metric, I examined its differential association with two types of threat-related judgements, untrustworthiness and aggressiveness. The face ratio (n of faces = 141) was more strongly linked to observers’ (n = 129) judgements of aggression than to their judgements of trust, although it is possible that this metric advertises threat potential more generally, of which aggression is a best indicator. In Chapter 4 (which extended some preliminary, additional findings from Chapter 3), I found that observers’ (n = 56) judgements of aggression were strongly correlated with the face ratio (n of faces = 25) even when men were bearded, suggesting that this metric could have been operational in our ancestral past when interactions likely involved bearded men. In Chapter 5, I combined effect sizes from experiments conducted from several independent labs and identified significant (albeit weak) associations between the face ratio and actual threat behaviour, and significant (and stronger) associations between the face ratio and judgements of threat potential. Together, this body of work provides initial evidence that the face ratio, and sensitivity to it, may be part of an evolved system designed for advertising and assessing threat in humans, akin to threat assessment systems identified in other species.
    • An In-depth Examination of Personality and Aggression Across Different Contexts

      MacDonell, Elliott; Department of Psychology
      Acts of aggression are associated with a variety of negative outcomes. Accordingly, research has aimed to identify the personality traits that give rise to different forms of aggressive behaviour. Recent work has indicated that the factor of Honesty-Humility is associated with a variety of deviant behaviours, including aggression towards others; however, the nuances of these relationships require further investigation. This dissertation aimed to address several gaps in this literature through three main studies. In Study 1, we extended previous findings to younger populations, examining the associations between Honesty-Humility and aggression longitudinally in a large sample of children and youth. These findings demonstrated a bidirectional relationship between Honesty-Humility and aggression over time, such that low levels of Honesty-Humility resulted in higher levels of aggression and vice versa. In Study 2, we explored the specific facets of Honesty-Humility to determine if they differentially predict proactive and reactive aggression. Despite the theoretical link between Modesty and reactive aggression, we found limited support for this association, especially when controlling for proactive aggression. Overall, the Sincerity and Fairness facets were found to strongly predict both forms of aggression. Lastly, Study 3 explored the associations between Honesty-Humility and deviance, aggression, exploitation, and victimization in a workplace context. Robust relationships were found between Honesty-Humility and several deviant behaviours, further emphasizing the importance of this trait. In particular, when provided with the opportunity to aggress, individuals low in Honesty-Humility were more likely to do so, regardless of their level of power in the situation. Collectively, these findings indicate that Honesty-Humility is the strongest predictor of aggressive and deviant behaviour among the broad factors of personality. However, this dissertation extends previous findings by demonstrating the applicability of Honesty-Humility across different contexts and by providing a nuanced understanding of the components responsible for this relationship.