  In the past decade a new style of evolutionary debunking argument has emerged that pits moral objectivism against the Darwinian origins of morals. While moral naturalism in some forms may not be at odds with understanding core moral beliefs as having a biological basis, such beliefs, it is argued, cannot embody objective moral knowledge in a robust sense. We must in effect choose between the Darwinian explanation and fully objective moral knowledge. Sharon Street (2006) presses this dilemma with careful attention to possible replies. She acknowledges that the kind of moral naturalism advanced by Peter Railton (1986) is compatible with the evolutionary basis of our core moral beliefs but argues that the price of embracing such naturalism is to give up thinking of moral truths as having the kind of objective status that moral philosophers often attribute to them. She is happy to pay that price, but others have contended that the assumption of objectivity, in particular moral realism, is built into how moral knowledge is commonly understood (Mackie 1977, Joyce 2006).For the latter group the dilemma presents an attack on the existence of moral knowledge, as most of us understand the concept. Since the aim of this essay is to review the issues concerning whether genuine moral knowledge is possible, we need to assess the merits of this debunking argument, paying close attention to how the ideal of objectivity is understood in this context.