Really taking Darwin and the naturalistic fallacy seriously: An objection to Rottschaefer and Martinsen

Out of a concern to respect the naturalistic fallacy, Ruse (1986) argues for the possibility of causal, but not justificatory, explanations of morality in terms of evolutionary processes. In a discussion of Ruse's work, Rottschaefer and Martinsen (1990) claim that he erroneously limits the explanatory scope of evolutionary concepts, because he fails to see that one can have objective moral properties without committing either of two forms of the naturalistic fallacy, if one holds that moral properties supervene on non-moral properties. In this short paper I argue that Rottschaefer and Martinsen's solution fails. If one takes moral properties to supervene on non-moral properties, then either one ends up committing one of the two forms of the naturalistic fallacy or else one is left postulating unbelievable brute metaphysical facts.