Looks that kill: Facial metrics and international conflict 1947-2010.

Research on psychology and foreign policy offers compelling evidence that leaders' predispositions to aggression influence their decisions to initiate military conflicts. However, most indicators of leader proclivities are limited both spatially and temporally, reducing their generalizability. To mitigate these issues, this study employs the facial width-to-height ratio (FWHR), a measure of aggression drawn from theories of evolutionary psychology, and available for most leaders in the post-World War II era. FWHR not only provides broad coverage but it also taps into a dimension of leader characteristics overlooked in most international conflict research. Empirical analysis of over 1,700 leaders across 174 countries during 1947-2010 reveals that higher-FWHR leaders are significantly more likely than their lower-FWHR counterparts to initiate conflict. The results are particularly strong early in a leader's tenure.