I first argue that the most puzzling aspect of our moral psychology from an evolutionary point of view (the ‘Hard Problem') is our inclination to treat moral demands and considerations as anything more than mere subjective preferences regarding our own and others' behavior. I discuss recent empirical evidence more precisely delineating the character of such moral objectification or externalization and then argue that existing evolutionary approaches abjectly fail to account for this crucial, salient, and robust feature of our moral psychology. I then propose a novel evolutionary hypothesis on which the adaptive advantages of such objectification arose from the opportunity it offered to increase the reliability (rather than strength) of moral motivation, and thus to increase our attractiveness to others as potential partners in exploitable forms of social interaction as humans evolved to become (unlike other primate species) default, domain-general cooperators. I draw on a wide range of both classic and recent empirical work to support this hypothesis, as well as explaining why the need to effectively advertise the objectification of our moral commitments in order to make ourselves more attractive cooperative partners renders it unlikely that any non-human organisms also externalize or objectify moral or prosocial motivation in this way. I conclude by revisiting the question of moral objectivity, illustrating how this evolutionary hypothesis enables us to understand why the status we ascribe to moral demands and considerations involves the distinctive (and otherwise puzzling) combination of objective and subjective elements that it does.