What inspires the willingness of humans to make their greatest exertions, to fight unto death with and for genetic strangers, a propensity to which no creature but humans seems subject? What determines the “fighting spirit” that enables one group of combatants to defeat another, all other things being equal? These are basic questions about human nature and warfare that an article by Whitehouse et al. endeavors to address. However, that article's arguments also bear directly on some of the world's current and most pressing crises. Thus, in recent remarks, President Obama endorsed the judgment of his US National Intelligence Director: “We underestimated the Viet Cong… we underestimated ISIL [the Islamic State] and overestimated the fighting capability of the Iraqi army…. It boils down to predicting the will to fight, which is an imponderable”. However, if Whitehouse et al.'s measures and findings are reliable and right, predicting who is willing to fight and who isn't could be ponderable indeed.