So-called evolutionary error theorists, such as Michael Ruse and Richard Joyce, have argued that naturalistic accounts of the moral sentiments lead us to adopt an error theory approach to morality. Roughly, the argument is that an appreciation of the etiology of those sentiments undermines any reason to think that they track moral truth and, furthermore, undermines any reason to think that moral truth actually exists. I argue that this approach offers us a false dichotomy between error theory and some form of moral realism. While accepting the presuppositions of the evolutionary error theorist, I argue that contract-based approaches to morality can be sensitive to those presuppositions while still vindicating morality. Invoking Stephen Darwall's distinction between contractualism and contractarianism, I go on to offer an evolutionary-based contractarianism.