Fearless dominance mediates the relationship between the facial width-to-height ratio and willingness to cheat

• Men who cheated had larger facial width-to-height ratios (fWHR) than men who did not cheat.
• Men who cheated had higher fearless dominance than men who did not cheat.
• Men’s fWHR were associated positively with their fearless dominance.
• Fearless dominance mediated the link between fWHR and cheating.

The facial width-to-height ratio (fWHR) is associated with a range of behaviours in men, but little is known about the underlying psychological mechanisms. We tested whether psychopathic personality traits were related to fWHR and mediated the link between this metric and cheating behaviour. Participants (146 men, 76 women) completed the Psychopathic Personality Inventory-Revised and rolled dice to determine the number of ballots allowed for entry into a lottery for a cash prize. Men’s willingness to cheat (entering more ballots than permitted) and their extent of cheating (number of additional ballots) was associated positively with fearless dominance and fWHR. Further, in men, fearless dominance was correlated with fWHR and mediated the relationship between fWHR and willingness to cheat, but not the extent of cheating. In women, there were no differences in fWHR or in personality traits between cheaters and non-cheaters. Psychopathic personality traits may thus underlie some fWHR-behaviour relationships in men.