Only All Naturalists Should Worry About Only One Evolutionary Debunking Argument

Evolutionary debunking arguments abound, but they're all murky where it counts most: exactly which epistemic principle combines with the facts of evolution to undermine moral realism? I'll identify some possible principles but show that most are false, spoiling the arguments built upon them. And every argument threatens only "representationalist" views of moral psychology, on which moral judgments rely on mental intermediaries, for example, sentiments. Only one argument remains a menace: a new "Argument from Symmetry." But it should worry only all naturalists, pressing a trilemma: abandon moral realism, accept a rationalism incongruous with naturalism, or reject naturalism. Nonnaturalists are free and clear.