Evolutionary debunking arguments, moral knowledge and underdetermination

Sharon Street's influential Darwinian Dilemma argues that moral realism is incompatible with moral knowledge. In this paper I argue that Street's argument cannot give us reason to reject moral realism. This is because the debunker's own arguments imply that our evidence for the claim that we have moral knowledge underdetermines its truth. Furthermore, the final part of the Street's argument, where she infers that moral realism must be false because we have moral knowledge, commits her to the view that underdetermining evidence cannot justify belief. This implies that the debunker is not justified in believing that we have moral knowledge. As a result, Street's debunking argument does not give us reason to reject realism (or accept anti-realism), even if we grant that they successfully establish the incompatibility of moral realism with our having moral knowledge.