The paper argues that Peter Singer's argument for utilitarianism is a failure, and that repairing the argument requires learning from the lesson of Rousseau and Kant. It points out that, like Singer, Rousseau's argument for the social contract comes unstuck because he cannot keep together his self-interested starting point (natural man) and his civic-minded conclusion. It then shows that Kant solved Rousseau's problem by building his civic man back into his natural man, to give a morality-friendly conception of human nature - and that, to solve his problem, Singer must do something comparable. It is further argued that the problematic starting point in self-interest reflects the influence of (some form of) evolutionary naturalism in both thinkers - but that it is a mistake to suppose that evolutionary naturalism requires such a starting point. So Singer can amend his argument without betraying its spirit - but his preference utilitarian conclusion cannot be guaranteed to be immune to the effects of such amendments.